EZRA (JONATHAN) DONAHAYE
E. Donahaye and S. Navarro
The influence of 20% carbon dioxide (CO2) and low pressure (13,300Pa/100 mm Hg) on the sensitivity of two dried fruit pests to methyl bromide (MB) was studied. Laboratory fumigations for up to 18 hours of eggs, larvae, pupae and adults of two species of Carpophilus (Coleoptera: Nitidulidae) revealed differences in sensitization between the treatments and between insect species and stages. For C. hemipterus, maximum sensitization to MB by CO2 was x 3.1 for 18 hour exposure to adults while maximum sensitization by low pressure was x 2.1 (for eggs). For C. mutilatus maximum sensitization to MB by CO2 was x 2.3 (for adults). At short exposures, differences in sensitization were marginal, while for 6 and 18 hour fumigations, 20% CO2 was generally more effective than low pressure.
E. Donahaye
Adult populations of the red flour beetle, Tribolium castaneum (Herbst), were exposed for 40 generations to an atmosphere containing 99.5% N2 and 0.5% O2 at 95% RH, in order to select a strain resistant to the low oxygen concentration (LOC) atmosphere. Selection pressure was maintained at between 50% and 70% mortality. At the 40th generation comparison of sensitivity between the selected strain and the original non-selected strain indicated a resistance factor at the 50% mortality level (LT50) of x 5.2. However, throughout the selections, log-time against probit-mortality curves remained roughly parallel from generation to generation and the slope remained low. These findings indicate a multiplicity of genetic factors that at a high level of selection contribute together towards an adaptation of the insects to survival in the LOC atmosphere. Removal of selection pressure from a sub-population of the selected strain from the 13th to 21st generation revealed that resistance was partially retained with a decrease in resistance factor of 23%. Although the study revealed that the insects were able to develop a strain resistant to hypoxia, exposures were at 95% RH to minimize the desiccation effect. This does not reflect field situations, where ambient relative humidities are generally below 70%.
E. Donahaye
Adult populations of the red flour beetle, Tribolium castaneum (Herbst), were exposed for 40 generations to an atmosphere containing 65% CO2, 20% O2 and 15% N2 at 95% RH, in order to select a strain resistant to high carbon dioxide concentration (HCC) atmosphere. Selection pressure was maintained at between 50% and 70% mortality. At the 40th generation, comparison of sensitivity between the selected strain and the original non-selected strain indicated a resistance factor at the 50% mortality level (LT50) of x 9.2. Throughout the selection process, log-time against probit-mortality lines remained roughly parallel and slope remained low and similar to that of the non-selected strain until the last generation. Implications are that at a high level of selection, multiple genetic factors continued to act together even at the 40th generation to select for adaptation to survival at high CO2 concentrations. Removal of selection pressure from a sub-population of the selected strain from the 13th to 21st generation revealed that resistance was partially retained with a decrease of 17% in the resistance factor. The modified atmosphere chosen in this study does not represent real-life situations where O2 concentrations are reduced by flushing with CO2, and intergranular relative humidities are generally not above 70%.
Ezra (Jonathan) Donahaye
Laboratory selections for resistance of Tribolium castaneum adults to low oxygen concentrations (LOC) and high carbon dioxide concentrations (HCC) have shown that this species is capable of developing low but significant levels of resistance to the respective modified atmospheres (MAs). Also resistance obtained in adults was partially transferred to the eggs and larvae. Studies on the modes of action of MAs, and the mechanisms of resistance in T. castaneum, indicate that the LOC resistant strain selected at 0.5% O2 was better able to survive anoxia than the non-selected strain. However metabolism during exposure to the LOC was mainly aerobic. Possibly mortality occurs when aerobic metabolism can no longer be maintained and is superceded by anaerobic metabolism with accumulation of toxic end-products. For exposure to HCC, death was the result of desiccation, and exhaustion of triglyceride (TG) energy reserves, and not by the prolonged narcotic effect of anesthesia, or the accumulation of toxic end-products. The resistant strain had greater TG reserves and was able to control water loss during exposure. Tests for susceptibility of both the LOC and HCC-selected and a non-selected strain of T. castaneum to methyl bromide and phosphine failed to reveal cross-resistance with these fumigants.
Donahaye, E., Navarro, S. and Miriam Rindner
The effect of exposure to 0 ° C, -5 ° C, -10° C, and -18° C, was investigated on all developmental stages of Carpophilus hemipterus L. and C. mutilatus Er.
Exposure to 0° C, caused relatively slow kill. Lethal exposure time (LT99) was longest (317.30 h) for larvae of C. hemipterus. At -5° C, exposure times required to control both species were also prolonged. Pupae were the most resistant stage, about 90 h being needed to produce 99 % kill of both species. At -10° C, mortality of both species was rapid, pupae being again the most resistant stage, 10.35 h was required for LT99. Exposure to -18° C caused very rapid kill of both species, LT99 of all stages being obtained within 2.25h.
E. Donahaye, S. Navarro, A. Ziv, Yehudit Blauschild and D. Weerasinghe
A trial was carried our in Sri Lanka on the outdoor storage for 6 months of locally grown paddy (type Nadu) in two hermetically sealed flexible liners termed 'storage cubes'. Insect infestations failed to develop in both cubes and TGM evaluations indicated a 0.33- 0.64% loss in dry weight due to metabolic activity. In one of the cubes, which contained paddy at higher moisture contents, a moisture condensation effect was revealed on the under-side of the upper liner. Losses by mould development resulting from this effect were estimated at 1.24%. Means for obviating this occurrence are proposed.
E. Donahaye, S. Navarro, Miriam Rindner and R. Dias
Experiments were carried out to investigate the influence of different modified atmospheres, low pressures alone, methyl bromide (MB) alone, and MB in combination with CO2 or low pressure, in causing nitidulid beetles to emigrate from infested dried fruit for which dates served as a model. All the treatments at 4 h and 16 h exposure and at 26° C, had a marked influence in causing insects to abandon the infested fruit. The most effective treatments at the two exposures were pressures of 50 mm Hg, and 1.4% O2 in air, both of which caused over 87% of the initial insect populations to emigrate from the fruit. At 4 h exposure 2.8% O2 was less effective than 100 mm Hg or MB. At 16 h exposure, MB+CO2 was third in effectiveness and 100 mm Hg was one of the least effective treatments.
E. Donahaye
The metabolic rates, as expressed by oxygen (O2) consumption, carbon dioxide (CO2) production, and losses in wet and dry weights, were examined for adults of three strains of the red flour beetle Tribolium castaneum (Herbst), during exposure to two modified atmospheres (MAs). Exposure of a strain selected for resistance over twenty-one generations to an atmosphere of 65% CO2, 20% O2 and the balance nitrogen (N2), termed a high carbon dioxide concentration atmosphere (HCC) and exposure of an unselected strain to HCC, showed considerable levels of aerobic metabolism during exposure. For the unselected strain water loss and mobilization of energy reserves were rapid and mortality was followed by rapid desiccation. For the HCC-resistant strain water balance was maintained and energy reserves were utilized more slowly over a prolonged period. Exposure of a strain selected for resistance over twenty-one generations to a low oxygen concentration atmosphere (LOC) of 0.5% O2 in N2, and an unselected strain to LOC, revealed that even at 0.5% O2, metabolism was largely aerobic in both strains. Maintenance of water balance was not a major factor causing mortality of either strain during exposure to LOC. In air, metabolic rates of both the resistant strains were lower than that of the unselected strain.
E. Donahaye, Daliah Zalach, and Miriam Rindner
All stages of a strain of Tribolium castaneum (Herbst) selected for resistance in the adult stage to a high carbon-dioxide-content atmosphere and of an unselected strain were exposed to the high-carbon-dioxide-content atmosphere. Similarly, all stages of a strain selected for resistance to a low-oxygen-content-atmosphere in the adult stage, and all stages from an unselected strain, were exposed to the low-oxygen-content atmosphere. For both selected strains, partial resistance was displayed by the eggs and larvae.
E. Donahaye
Examination of the rates of development, rates of oviposition and body weights of three strains of the red flour beetle Tribolium castaneum (Herbst) at the 21st generation, revealed that a strain selected for resistance to hypoxia was significantly heavier at the pupal and adult stages than a strain developed for resistance to hypercarbia and an unselected strain. It also exhibited a more prolonged developmental range and a lower oviposition rate than the unselected strain. The strain selected for resistance to hypercarbia was also significantly heavier than the unselected strain, and the oviposition rate was also lower although not significantly. When the three strains were subjected to starvation at the 26th generation, it was shown that metabolism in both selected strains proceeded at a lower rate than in the unselected strain and consequently the selected strains survived for much longer periods.
E. Donahaye and Miriam Rindner
Two strains of Tribolium castaneum, one resistant to a low oxygen content atmosphere (LOC) and another resistant to a high carbon dioxide content atmosphere (HCC), were used to test the specificity of their laboratory-induced resistance. The LOC-selected strain was exposed to HCC and shown to be susceptible, while the HCC-selected strain, upon exposure to LOC, was also susceptible, indicating that survival under hypoxia and hypercarbia require different adaptive mechanisms. Exposure of the LOC-selected strain to anoxia revealed greater tolerance than an unselected strain. Exposure of both strains to a 60:8:32 mixture of CO2, O2, and N2 revealed that both strains were more resistant than an unselected strain. Exposure of the selected strains to methyl bromide and phosphine failed to reveal any cross-resistance imparted to the insects against the fumigants.
J. E. Donahaye, S. Navarro and Miriam Rindner
In laboratory experiments, larval, pupal, and adult stages of the nitidulid beetles Carpophilus hemipterus (L.) and Urophorus humeralis F. were exposed to simulated burner-gas concentrations at three temperatures of 26° C, 30° C, and 35° C. The gas concentrations were: 1%O2, 85%N2, 14%CO2; 2%O2, 84.7%N2, 13.3%CO2; 3%O2, 85%N2, 12%CO2 -all at 75% relative humidity. For all insects submitted to the modified atmosphere (MA) containing 3%O2 at 26° C, exposure times to produce 95% mortality were 196 h. To obtain the same mortality level with the MA containing 1%O2 at 35° C, 60 h were required. Comparison of exposure times required to produce 50% kill (LT50 ) showed that the effect of temperature on treatment efficacy was most pronounced at the 1% O2 level where for the three stages of both species tested, values of LT50 at 26° C were about half those at 35° C. However, at 3%O2 and 35° C, LT50 levels were only marginally reduced.
E. J. Donahaye, S. Navarro and Miriam Rindner
The effect of exposure to 0° C, -5° C, -10° C and -18° C was investigated on all developmental stages of the stored-product beetles Tribolium castaneum Herbst. and Oryzaephilus surinamensis (L.), and the moth Ephestia cautella (Walker). For all three species the time to produce 99% kill of the least sensitive stage of the least sensitive species ranged from 233 h for adults of O. surinamensis at 0° C, 41 h for adults of O. surinamensis at -5° C, 6.1 h for eggs of E. cautella at -10° C, to 2.6 h for eggs of E. cautella at -18° C. Interspecific and intraspecific comparisons of mortalities were made at the LT50 level, due to the wide confidence limits at high mortalities especially at the lower temperatures. For T. castaneum the adult was least sensitive at 0° C and -5° C and the pupa at -10° C and -18° C. For E. cautella the least sensitive stage at 0oC and -5oC, was the adult, at -10° C the egg and -18° C the larva. For O. surinamensis the least sensitive stage at 0° C, -5° C, and -18° C was the adult, and at -10° C the pupa.
E. J. Donahaye S. Navarro, M. Rindner and A. Azrieli
In laboratory experiments, egg, larval, pupal, and adult stages of the red flour beetle Tribolium castaneum (Herbst). were exposed to three low oxygen concentrations realistically obtainable under hermetic storage conditions, at three temperatures of 26° C, 30° C, and 35° C. The gas concentrations were: 1%O2, 85%N2, 14%CO2; 2%O2, 84.7%N2, 13.3%CO2; 3%O2, 85%N2, 12%CO2.- all at 75% relative humidity. When exposed to the 3% O2 level at 26° C, adults were most tolerant with a mortality of 70.5% when exposed for 10 days. To obtain 99% mortality at 35° C with the atmosphere containing 1%O2, a maximum of only 44 h was required for the most tolerant stage, namely the pupa. Comparison of exposure times required to produce 50% kill (LT50 ) showed that the effect of temperature on mortality rates was pronounced at all three levels of O2 where for all the insect stages, values of LT50 at 35° C ranged between 0.16 and 0.5 times those at 26° C. The insects were also submitted to a gas mixture containing 1% O2 in 99% N2 representing a mixture obtainable by N2 flushing techniques. At the higher temperatures, differences in mortality between those obtained on exposure to 1%O2: 85%N2:14%CO2 were not significant. However, at 26° C, mortality levels of insects exposed to this mixture were lower, particularly for adults and eggs.
E.J Donahaye, S. Navarro, R. Diaz and Miriam Rindner
Two species of narcissus fly attack the bulbs of Narcissus and Amaryllis, posing a serious quarantine threat when these crops are exported from Israel. The only available fumigant for rapid treatment is methyl bromide (MB). However, recent indications of phytotoxic effects on these bulbs required re-evaluating the fumigation schedule.
The sensitivities of the large narcissus fly (Merodon eques F.) and the small narcissus fly (Eumerus spp.) to MB were examined in the laboratory. Maggots of both species and pupae of Eumerus were obtained from infested narcissus bulbs and exposed in glass chambers at 28@C to different dosages of MB for 4 h periods. Because the Merodon develops inside the bulb, maggots of this species were transferred to cells hollowed out inside sound bulbs, and the bulbs were then placed inside the fumigation chambers. For Eumerus, where infestation is superficial, maggots and pupae were suspended in cages inside the fumigation chambers. Probit analyses of mortalities revealed that the dose required to obtain 99% kill (LD,'') was 20.4 g/m3 for Merodon sp., whereas for Eumerus larvae and pupae it was 8.6 and 6.5 g/m3, respectively. The high dosage required to kill Merodon may be attributed to the necessity that the gas penetrate to the target site.
Donahaye, E.J., Andales, S.C., Chernoguz, D., Navarro, S., Azrieli, A. and Miriam Rindner
Laboratory experiments were undertaken to determine the effect of temperature and moisture content (MC) on respiration of paddy. The experiments were carried out in glass jars (500 ml fi1led with paddy, conditioned to four target levels of MC corresponding to the following water activities (aw): 0.75, 0.80, O85 and 0.90, and held at 25, 30 and 35° C respectively. The trials were carried out using low quality paddy (rain-damaged) with 23% germination, and high quality paddy with 91% germination. A linear relationship was found between respiration rates expressed as log of oxygen consumption in mg O2/100 g dry matter/day plotted against paddy MC. for 18% MC at 35° C, respiration rate of high quality paddy was 20.361 mg 02/100 g dry matter/day, and for 14% MC at 25° C it was 0.604 mg O2/100 g dry matter/day. For the same temperatures and MCs, the low quality paddy gave values of 17.175 and 0.585 mg O2/100 g dry matter/day respectively.
Self regulated atmospheres to prevent fungal damage in moist paddy
Donahaye, E. and Andales S
The objective of this project was to provide a solution to the acute problem in far-eastern Asia where paddy-rice is harvested at high moisture contents (MCs) during the monsoon season. This paddy must then be dried rapidly to a safe MC in order to prevent it from molding and rotting. However, if the paddy is dried rapidly from about 30% to the required "safe" MC, the grains suffer stress resulting in cracking and breakage. To overcome this problem a two-stage drying procedure has been advocated where the paddy is initially dried to 18% (intermediate MC), at which stage yeast and bacterial activity are suppressed, followed by a second stage drying from 18 to 14% MC to prevent the development of storage molds. However, the drying problem is compounded by the fact that most farmers do not have flash dryers and are obliged to sell their grain directly to the traders. Even if flash dryers are available, insufficient capacity of second stage dryers creates a bottleneck at harvest time.
Our project was designed to develop a technology that would enable farmers to overcome this bottleneck at the second drying stage by providing them with a means of storing the intermediate MC paddy under tightly sealed conditions and thereby prevent spoilage for prolonged periods until drying by sun or machine is again an available option.
The present policy of the Filipino government is directed at providing small scale farmer cooperatives with on-site storage units so as to decentralize storage of the national grain reserve as well as provide rural communities with a higher level of food security. Implementation of this policy is under way, and already the concept of sealed storage to protect dry grain from insect infestation has been widely promoted together with the distribution of flexible plastic outdoor storage cubes that were developed by ARO and BPRE as the outcome of a previous CDR project (C7-053). In 1998, about 200 units of these storage structures were purchased and distributed to farmers' cooperative recipients nationwide. Recently, the government has purchased an additional 300 units for distribution among farmer cooperatives through soft-loans. This is being done as a mitigating measure in anticipation of "La Niña".
However, the problem of harvesting moist paddy in the rainy season still remains. Although both the previously developed storage technology, and the present one are based on the same principle of hermetic storage, the objective of the present project was to employ the principle of self-regulated atmospheres caused by aerobic metabolism in order to arrest fungal development and preserve grain quality in paddy of intermediate MC. Here, to prevent spoilage, oxygen depletion must be much greater and more rapid than that required to control insects, and it was anticipated that this would require a higher level of hermetic seal than that required for insect disinfestation.
The first two questions to be answered, before field trials could be initiated, were - do the rates of oxygen depletion obtainable by sealed storage of moist paddy prevent mold proliferation sufficiently in the damp grain; and, - can hermetic storage of intermediate MC grain, be carried out without having a deleterious influence on the aroma, taste and cooking qualities of the rice?
Both these aspects were studied during the first and second years with laboratory studies in the Philippines being undertaken on the effect of hermetically sealed "moist" paddy stored for different time periods on different quality parameters including milling and organoleptic characteristics; while in Israel, studies with the same paddy and also wheat were directed at evaluating rates of aerobic metabolism at different moisture contents and temperatures as a basis for determining rates of oxygen depletion within the storage structures.
In the first year a flexible storage structure of 10 tons capacity was manufactured from a plastic laminate chosen from a series of materials that were screened to test their permeability to oxygen and carbon dioxide. This structure was field-tested prior to shipping for paddy storage trials to be undertaken in the Philippines.
Although calculations indicated that the low permeability of the liner material would give a sufficient seal to reproduce laboratory conditions, an additional factor was anticipated to have an influence on the storage environment under field conditions. This was the development of air convection currents within the stack that carry moisture and deposit it at the top layer. These currents develop when temperature gradients are formed as a result of diurnal temperature fluctuations. This phenomenon was noted in the previous study when storage cubes were set-up in un-shaded sites. As a counter measure, an insulating layer of rice hulls was placed over the top layer of bags and this solution was adopted as standard procedure. However, for the storage of intermediate MC grain the situation is much more critical since any rise in MC above 18% is liable to enable the anaerobic metabolism of bacteria and yeasts that have a strong influence on grain quality, particularly taste and aroma.
An improved solution developed during this project was the use of an external reflective shade cover placed over the storage cube in order to reduce temperature gradients within the grain and thereby minimize the moisture migration phenomenon. Initial trials that were carried out in both countries in the second year, were inconclusive. However, after modifications, further trials carried out during the third year in both countries gave positive results that have led to adoption of this concept for all outdoor storage in plastic liners, and inclusion of reflective covers in the standard commercial kits.
It was clearly demonstrated in the first year that the rates of oxygen depletion in hermetically sealed moist paddy could prevent mold proliferation, but the effects of hermetic storage upon paddy quality took longer to evaluate than planned, as this required repeat experiments to enable in-depth evaluations of cooking and acceptability parameters that were carried out by Prof. Del Mundo at the University of the Philippines, Los Baños after 1, 3 and 6 months of storage. The project findings indicated that after 1 month, quality of sealed paddy stored at up to 18%MC had not deteriorated. However, further evaluations made on paddy stored hermetically for 1, 3 and 6 months under both laboratory and field conditions confirmed that after the first month of storage the quality of moist paddy (16-18% MC) deteriorated progressively and the grain was no longer acceptable by the taste panels. These findings enable the following tentative recommendations to be made for paddy storage duration:
For 18% MC one (1) month
For 17% MC one (1) month (not confirmed by field trials)
For 16% MC can be extended to two (2) months (not confirmed by field trials)
For 15% MC can be extended to three (3) months (not confirmed by field trials)
For 14% MC still the recommended level for long term paddy storage
In conclusion, the present widespread implementation of the hermetic storage technology at the cooperative and village level throughout the Philippines has been backed up with BPRE initiated "on-the-spot" extension courses. Many aspects of this technology have not yet been explored especially field validation of the laboratory findings at 15 - 17% MC. However will we anticipate that this enterprise will serve as a starting point for the adoption of hermetic storage to protect paddy of intermediate MC until it can be dried.
E. J. Donahaye and S. Navarro
The quantities of energy reserves and their utilization were examined in adults of three strains of Tribolium castaneum (Herbst) before and during exposure to two modified atmospheres. It was shown that a strain selected for resistance to high CO2 content (HCC) contained significantly greater triacylglycerol, (TG) reserves than a strain selected for resistance to low O2 concentration (LOC) and an unselected strain. During exposure to HCC, the major energy source was TGs, most of which were consumed during exposure; TG utilization by the unselected strain was more rapid than that by the HCC-selected strain. During exposure to LOC, TGs were also utilized, but to a lesser extent, revealing an indication of more attenuated mobilization of energy reserves. Here, too, TG utilization by the unselected strain was more rapid than by the LOC-selected strain. The function of TGs in enabling the insects to maintain their water balance during exposure was considered.
Concentrations of polysaccharides and glucose were low in all strains and although they decreased during exposure to MAs, their contribution to metabolic energy supply during exposure was small.
Donahaye, E.J., Navarro, S., Miriam Rindner and Azrieli, A
Galleria mellonella (L.), is a cosmopolitan pest, causing serious economic damage to honey-bee combs during storage. Efforts are being made in Israel to replace existing control methods against this pest based on fumigation, with an environmentally friendly treatment that affords long-term protection. For this purpose, application of modified atmospheres ( MAs ) by single shot flushing with carbon dioxide (CO2 ) has been developed using flexible treatment chambers, and modified transport containers. This laboratory study was made to provide information on the effect of exposure period on wax moth mortality over the range of MA concentrations and temperatures encountered in practice.
Three MAs, namely 80%, 70% and 60% CO2 in air, were supplied at 75% r. h. to exposure chambers held at 26° C and 30° C. Eggs (24 -48 h), larvae (12 d), pupae (O - 48 h) and adults (0 - 24 h) were exposed in the chambers for periods ranging from eight hours to twelve days. Mortalities were recorded and subjected to probit analysis except for eggs where exposure time till no-survival was recorded. For all treatments, adults were the most sensitive, and eggs the least sensitive, with sensitivity being consistently higher at 30° C. It was concluded that 10 days exposure to a range of 90 - 60% CO2 will give complete control of all stages.
Ezra Jonathan Donahaye
There is an increasing dichotomy between the demands of the first world for quality food uncontaminated by insecticidal residues. and the desperate need of third-world populations to maintain and protect their harvested grain from the deprivations of insects, so as to maintain a minimum level of food security. Fumigation is widely regarded as a non-residual treatment and fumigation with phosphine will continue for the immediate future as the mainstay against insect infestation. However, to ensure its continued use, insect resistance to phosphine must be countered by more efficient application techniques. Already, available alternative control technologies such as hermetic storage and the use of controlled atmospheres using either nitrogen or carbon dioxide also rely heavily on well-sealed storage structures, that are rarely available in rigid silos, but easily obtainable with flexible plastic liners. Aeration systems to cool grain bulks and thereby prevent insect development, are being widely used even in warm climates but are only applicable for bulk grain. Other non-residual treatments such as mechanical impaction, irradiation, biological control or heating, arc suitable for high-quality commodities or niche situations.
Jonathan Donahaye, Shlomo Navarro, Filipinas Caliboso, Glory Sabio, Gemma Mallo and Joel Dator.
A sealed structure that provides protection of grain without the use of chemical pesticides and termed "Volcani cube" was used in these experiments. A major advantage of the Volcani cube is that it can be used to safely store grain outdoors when no suitable storage buildings are available. However, under tropical conditions, when grain is stored in the open with no shade, ambient diurnal temperature fluctuations, can create temperature gradients within the stack that cause convection currents to carry moisture to the upper layers of grain. To overcome this, an upper insulating layer of bags containing straw or husks was employed. Under Filipino conditions this solution enables safe storage of maize and paddy for periods of up to three months, while for more extended periods the top moistened layer of husks should be replaced with dry material. This method, although solving the problem, suffered from the inherent disadvantages of reduction in effective storage capacity, the necessity to procure and transport material to fill the bags, and the added expense of bags not used for storing grain.
In a search to develop an alternative inexpensive and convenient method of insulating the stack from diurnal temperature fluctuations, the use of a shade screen placed above the cube was investigated. This material described as a knitted thermal screen is formed from aluminum coated high density polyethylene threads.
Trials in Israel and the Philippines showed that the reflective covers had a strong attenuating influence on temperature gradients and condensation at the top of the cubes on condition that a space for free movement of air was allowed between the cover and the plastic liner. For dry paddy, it was shown that after five months storage under a reflective cover, no perceptible increase in moisture content was found at the top of the stack and the grain remained in good condition.
E. Donahaye, S. Navarro, Miriam Rindner, Avi Azrieli
Methyl bromide has been used for controlling dry fruit pests in storage. To develop an alternative treatment which would prevent insect development and preserve fruit quality a controlled atmosphere of 60-80% carbon dioxide was used within a 151 m3 plastic chamber partially filled with 30 tons of dates stacked in crates on pallets. At the initial purge phase the desired carbon dioxide concentration was obtained in the chamber within one hour by introducing the gas under high pressure. An intermittent maintenance phase was then applied for 4.5 months using approximately 0.8 kg carbon dioxide per day. At the end of storage, quality of the treated dates was compared to controls stored at -18°C. No significant difference was found between the treated dates and controls. The insect population was effectively controlled and reinfestation prevented. This technology is proposed for the treatment of stored dates, and may also be applicable to other dried fruits, to control pests and maintain quality.
Jonathan Donahaye
The search for non-chemical methods of controlling insect infestations in stored products, has increased in intensity as public awareness has risen with respect to pesticide residues in food and their harmful influence on the environment. Several lines of approach were thoroughly investigated and documented some 30 to 40 years ago and then stagnated or were abandoned because chemical control methods were cheaper and more convenient. Fortunately many research groups are now in a "rethink" mode as a direct result of pressure from national and international legislative bodies that are fast reducing the range of existing chemical options, while the development of new chemicals for the stored product market has become prohibitively expensive. Today, funding is available for the development of methyl bromide alternatives, where the major requirement is rapid kill. Tomorrow phosphine fumigation, which has long been the mainstay of the grain storage industry, may also become restricted and the battle is already being waged.
Many of the non-residual control methods have "niche" potential such as the use of impact forces in the flour industry, the use of the two extreme ranges of the electro-magnetic spectrum (radio frequencies and ionizing irradiation) for high-value commodities, or even biological control in situations where insect contamination is not a problem.
However, the brightest available technologies for broad-spectrum application in the developed world appear to be the use of aeration where ambient temperatures can be used to cool grain bulks to below the threshold for insect development. In the developing world where climates are usually tropical and the prevalence of bag storage often precludes aeration for insect prevention and control, the application of modified atmospheres, and most particularly the special case of sealed (hermetic) storage that makes use of biogenerated atmospheres, has a tremendous potential that is now being exploited.
The manipulation of combined approaches such as controlled atmospheres at high temperatures or at high pressures, are also being studied as promising alternatives to conventional fumigation.
ARO-AMERICAN JEWISH WORLD SERVICE (AJWS) GRAIN STORAGE PROJECT
E. Donahaye and S. Navarro
This 3-year project was concluded in December 1990. The overall objective was to improve food security for farming communities of the developing nations. For this purpose a flexible plastic storage structure was developed, to provide hermetic storage of cereal grains for the small-scale farmer, who was thereby enabled to retain grain beyond the harvest season and sell when prices are optimal. Storage trials in Israel and in several countries of Asia and Africa provided rigorous testing of the system and facilitated the introduction of improvements. The trial program was undertaken with the assistance of three technicians who were trained both to undertake the in-country storage trials and to provide the necessary extension services to the local farmers. During this project, several field trials were conducted to evaluate the suitability of the storage systems in eight developing countries.
Comparison of the sensitivity of the developmental stages of three strains of the red flour beetle, Tribouum castaneum (Coleoptera: Tenebrionidae), to modilied atmospheres
E. Donahaye, D. Zalach and M. Rindner
All stages of a strain of Tribolium castaneum (Herbst) selected for resistance in the adult stage to a high-CO2-content atmosphere (HCC), and of an unselected strain were exposed to an HCC atmosphere. Similarly, all stages of a strain selected for resistance to a low-O2-content atmosphere (LOC) in the adult stage, and all stages from a unselected strain, were exposed to an LOC atmosphere. For both selected strains, partial resistance was displayed by the eggs and larvae.
Low temperature as an alternative to fumigation for disinfesting dried fruit from three insect species
E J Donahaye, S. Navarro and M. Rindner
The effects of exposure to 0, -5, -10 and -18°C were investigated for all developmental stages of the stored-product beetles Tribolium castaneum Herbst. and Oryzaephilus surinamensis (L.), and the moth Ephestia cautella (Walker). For all three species, the time to achieve a 99% kill of the least sensitive stage of the least sensitive species ranged from 233 h for adults of O. surinamensis at 0°C, 41 h for adults of O. surinamensis at -5°C, 6.1 h for
eggs of E. cautella at -10°C, to 2.6 h for eggs of E. cautella at -18°C. Interspecific and intraspecific comparisons of mortalities were made at the LT50 level, due to the wide confidence limits at high mortalities especially at the lower temperatures. For T. castaneum the adult was least sensitive at 0°C and -5°C and the pupa at -10°C and -18°C. For E. cautella the least sensitive stage at 0°C and -5°C, was the adult, at -10°C the egg and -18°C the larva. For O. surinamensis the least sensitive stage at 0°C, -5°C, and -18°C was the adult, and at -10°C the pupa.
Studies on aeration with refrigerated air-iii. Chilling of wheat with a modified chilling unit
E. Donahaye, S. Navarro and M. Calderon
Abstract-Two trials on the cooling of grain with refrigerated air are described. The chilling unit had the fan positioned after the evaporator to lower relative humidity of the cooled air entering the grain. A bin containing 699 metric tonnes of wheat was cooled in summer from 30-37¡C to 18-19¡C in 160 hr at an energy consumption of 4.6 kW/hr/tonne. The second bin containing 863 tonnes of wheat was cooled in winter from temperatures of up to 42¡C to 15-21.5¡C in 236 hr at an energy consumption of 4.7 kW/hr/tonne. It was shown that grain was not moistened as a result of cooling. The importance of controlling both air temperature and humidity in the cooling system are discussed and this method is compared with aeration using ambient air.
Observations on the life cycle of Caryedon gonagra (F) on its natural hosts in Israel, Acacia spirocarpa and A. tortilis
E. Donahaye, S. Navarro, and M. Calderon
The life cycle of Caryedon gonagra F on its natural hosts the seeds of Acacia spirocarpa and A. tortilis in the Negev and Dead Sea depression is described. Observations showed that the insect develops two overlapping generations during the year and passes the winter just below ground level as a larva, or pre-pupa within the pupal cocoon. A list of parasites associated with C. gonagra is provided.
Laboratory cultures revealed that C. gonagra lays eggs on, and develops within, dry seeds of A. spirocarpa. The developmental time from egg to emergence of the larva from the seed is about 23 days, and from construction of the cocoon until adult emergence, from three to seven months.
Observations on the length of time spent in the pupal cocoon showed that under room conditions this period extended up to 750 days or more, while under controlled conditions (26¡C, 70 %RH) it lasted from 60 to 210 days with a maximum emergence period after 120 to 150 days. In cocoons taken from C. gonagra cultures on groundnuts this period lasted from 15 to 90 days only with a peak emergence after 15 to 30 days.
These results indicate that the larvae in the field enter a state of dormancy after having spun the pupal cocoon in the autumn.
Storage of Barley in an Underground Pit Sealed with a Polyethylene Liner
E. Donahaye, S. Navarro and M. Calderon
Abstract-Fifty tons of locally grown barley were stored in an underground pit hermetically sealed inside a polyethylene liner at Kibbutz Lahav. Gas measurements and observations showed that a satisfactory hermetic seal was obtained within the liner after seven weeks of storage (1.0-3 2 per cent O2) However, the efficiency of the seal was reduced by the gnawing activity of rodents which damaged the liner, and this appears to be a limiting factor for this type of storage. Changes in moisture content and in germination power were minimal during the storage period. Marked seasonal temperature changes were only recorded at the periphery of the grain bulk, while at the centre the temperature remained stable. The barley which was removed after 15 months of storage, during nine of which the liner was sealed, was clean, of natural brightness and colour, of low moisture content, and uninfested.
A Sealed Structure for grain storage by small-scale farmers :GrainSafe
Jonathan E.Donahaye and Shlomo Navarro
Throughout the developing world, the on-farm storage of harvested grain by small-scale farmers is critically important in providing food security for rural communities. In the past, traditional storage structures provided some protection against storage losses, particularly by insects and rodents, though annual losses at the village level which are estimated to run at between 5 and 10% were usually considered as inevitable. Attempts to reduce these losses through the introduction of modern storage technologies have consistently failed being either socio-economically unacceptable, or inappropriate to local climatic conditions and agro-technical practices.
Our objective was to develop a storage structure with the following characteristics which are essential pre-conditions to acceptance by farmers throughout the developing world:
- Design basically similar to those of many traditional storage structures (cylindrical container, raised above ground on a platform, with an upper loading port and a lower spout to remove the grain).
b) Storage capacity appropriate to harvest volumes of small-scale and subsistence farmers.
- Reduction in cost of manufacture by incorporation of certain elements of the structure that are usually freely obtainable locally (raised platform, straw roof) and contribute to the acceptability of the structure by farming societies.
- Achievement of a minimal and affordable price with an anticipated life-time of several years.
- Application of a method of grain preservation that is environmentally sound, and user friendly, and does not require application of chemical pesticides.
The innovative idea that formed the basis of this project was to develop a structure where the grain is contained within a sealed flexible plastic liner, while rigidity is obtained using a thin but rigid polypropylene (PP) sheath. Unique features in the structure were designed to enable the grain to be loaded and unloaded, with the possibility of periodic removal of limited quantities of grain, after which the openings would be sealed. By these means it was deemed possible to maintain the storability of the grain, without affecting significantly the principle of gas-tightness needed for control of insect pests. This storage system would obviate the need for employing residual insecticides and fumigants with the accompanying hazards they pose to the users and the environment.
The study carried out in Israel during 1997-1998, consisted of three consecutive trials of limited duration, followed by evaluation of the findings after each trial. These evaluations formed the basis for changes, both structural and procedural, which were made and then tested in the following trial. The fourth trial which was of much longer duration was carried out in a prototype structure which, with only minor changes, is now deemed suitable for field testing in developing countries.
A scientific report on the third trial was prepared for presentation at the Seventh International Working Conference on Stored-Product Protection, held in Beijing China in October of 1998. This report will shortly be published, and since it is an integral part of the work accomplished in this project, it is provided here as Annex 1.
To summarize, through the development of a series of prototype storage structures, a structure has been obtained that we believe will fulfil the storage needs of small scale farmers at a minimal and affordable cost. This now needs to be field tested abroad.
The influence of temperature on the sensitivity of two nitidulid beetles to low oxygen concentration
J. E. Donahaye, S. Navarro and M. Rindner
In laboratory experiments, larval, pupal, and adult stages of the nitidulid beetles Carpophilus hemipterus (L.) and Urophorus humeralis (F.) were exposed to simulated burner-gas concentration at three temperatures or 26, 30, and 35¡C. The gas concentrations were: 1% O2, 85% N2, 14%CO2; 2%O2, 84.7%N2, 13.3%CO2; 3%O2, 85%N2, 12%CO2-all at 75% relative humidity. For all insects submitted to the modified atmosphere (MA) containing 3%O2 at 26¡C, exposure time to produce 95% mortality was 196 hours. To obtain the same mortality level with the MA containing 1%O2 at 35°C 60 hours were required. Comparison of exposure times required to produce 50% kill (LT50) showed that the effect of temperature on treatment efficacy was most pronounced at the 1% O2 level where for the three stages of both species tested, values of LT'50 at 26°C were about half those at 35°C. However, at 3%O2 and 35°C, LT50 levels were only marginally reduced.
Quality preservation of moist paddy under hermetic conditions
Donahaye, E.J., Navarro, S., Andales, S., Angelita M. Del Mundo,
Filipinas Caliboso, Glory Sabio, Angelina Felix, Miriam Rindner, Azrieli, A. and Dias, R.
Two laboratory studies were carried out to evaluate the influence of hermetic storage on the quality conservation of paddy at different water activities. Five moisture content (M.C.) levels of paddy were used, namely, 14, 15, 16, 17 and 18% w.b., approximately corresponding to the following water activities: 0.75, 0.80, 0.85, 0.88 and 0.90 aw. Quality evaluations were carried out after five storage periods, namely: 0, 1, 2, 3, 4 weeks for the first experiment and seven storage periods, namely 0, 1, 2, 3, 4, 5, 6 months for the second experiment. The entire study was undertaken at room temperatures of ~ 29° to 30°C prevailing in the Philippines. Cooked rice aroma, taste, tenderness, cohesiveness, color and gloss were found to be negatively correlated with moisture content (m.c.) and storage duration of the paddy. The poor acceptability and preference-scores for cooked milled rice samples from paddy stored hermetically at 16% to 18% m.c. was primarily dictated by the presence of fermented smell in these samples. In the raw form, wholeness of grains and color were found to have a significant negative correlation with m.c. and storage duration. Analysis of microfloral loads and bacteria revealed an increase in bacterial counts for the paddy held at 17% and 18% m.c.
Field trials using sealed flexible storage structures of 10 tons capacity were undertaken. It was clearly demonstrated that the rates of oxygen depletion in hermetically sealed 18% m.c. paddy could prevent mold proliferation. The effects of hermetic storage upon paddy quality were also evaluated using cooking and acceptability parameters obtained after 1, 3 and 6 months of storage. The findings indicated that after 1 month, quality of sealed paddy stored at 18% m.c. had not deteriorated perceptibly. However, further evaluations made on paddy stored hermetically for 1, 3 and 6 months under both laboratory and field conditions confirmed that after the first month of storage the quality of moist paddy (16-18% m.c.) deteriorated progressively and the grain was no longer acceptable to the taste panels.
Reflective covers to prevent condensation in sealed storages in the tropics
Donahaye, E.J., Navarro, S., Glory Sabio, Miriam Rindner,
Azrieli, A. and Dias, R.
A sealed structure (the 'Volcani Cube') that provides protection to grain without the use of chemical pesticides was used in these experiments. A major advantage of the Volcani Cube is that it can be used to safely store grain outdoors where no suitable storage buildings are available. Under tropical conditions, when grain is stored in the open with no shade, ambient diurnal temperature fluctuations, can create temperature gradients within the stack that cause convection currents to carry moisture to the upper layers of grain. To overcome this effect, an upper insulating layer of bags containing straw or husks was employed. Under tropical climates this solution enables safe storage of maize and paddy for periods of up to 3 months; for more extended periods the top moistened layer of husks should be replaced with dry material. In a search to develop an alternative inexpensive and convenient method of insulating the stack from diurnal temperature fluctuations, the use of a shade screen placed above the cube was investigated. This material described as a knitted thermal screen is formed from aluminum coated high-density polyethylene threads. Trials conducted with Volcani Cubes in tropical and subtropical climates showed that grain is protected under sealed storage by maintaining the number of live insects below the threshold of economic damage without the need for pesticides. For dry paddy, it was shown that after 5 months storage under a reflective cover, no perceptible increase in moisture content was found at the top of the stack and the grain remained in good condition.
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