Emigration and control of nitidulid beetles from dates using heat
Shlomo Navarro*, Simcha Finkelman, Miriam Rindner, Refael Dias
Department of Food Science, Agricultural Research Organization, The Volcani Center, P.O.Box 6, Bet Dagan 50250, Israel
Abstract: Dates are subject to infestation by nitidulid beetles during and after harvest. Fumigation of dried fruits with methyl bromide (MB) upon arrival at the packing plant effectively controls infestation and causes a high proportion of larvae and adults to emigrate from the fruit before they succumb. This work was undertaken to investigate the effectiveness of heat treatment as an alternative to MB, which would remove insects from the dates, prevent insect development, and preserve fruit quality. Dates grown in Israel served as a model for development of the technology designed to be integrated into the pre-storage drying process. The test insects were Carpophilus hemipterus larvae reared on a synthetic food medium and held at 26ºC and 75% relative humidity. Artificial feeding sites destined to simulate the dates were prepared consisting of cardboard rectangles placed on food medium contained in Petri dishes. Exposure to different treatments was carried out in 2.54 L desiccators. For each treatment, exposure times of 2 h after the feeding sites reached the target temperature were employed. Temperatures of 40º, 45º, 50º and 55ºC were tested. The ratio of the number of larvae found outside the feeding sites to the total number of insects was used to describe the term "percent disinfestation". Disinfestation was greatest (92.3%) at 50ºC and the difference was highly significant from exposure at 40º and 55ºC. At 50º and 55ºC 100% mortality was obtained. Conventional drying temperatures for most date varieties are in the range of 50º to 55ºC. Since percent disinfestation and control was most effective at 50ºC, application of heat appears an encouraging solution for the treatment of dates as a replacement to MB. The laboratory findings served as basis for two field trials carried out at a date drying station. This consisted of a hot-house holding pallets of stacked crated dates arranged in rows and covered by plastic liners to form drying ducts. One extremity of each duct was connected to a thermostatically control chamber supplying solar heated air, and the other end appended to large fans set to extract air from the ducts. Crates with artificially infested dates were positioned at strategic sites and the drying pass of 45ºC was preceded by a 2 hour pass at a target temperature of 50ºC. Results showed that although mortality after 2 h was incomplete at some sites, disinfestations was very high, and over the normal drying period of up to 72 h mortality would have been complete.
Key words: dried fruit, dates, disinfestation, Nitidulid beetles, Carpophilus spp., heat treatment, methyl bromide alternatives, IPM, storage pest control
