Efficacy O"ftemperature Treatments for Insect Disinfestation of Dried Fruits and Nuts

In order to determine the most resistant stage to various high temperature treatments for disinfesting dried fruits and nuts of postharvest insect pests, effect of different Indianmeal moth (lMM) and navel orangeworm (NOW) egg ages on response to heat was estimated. Of the ages treated, 9 :i: 8 hr old IMM eggs, and 42 :i: 6 hr old NOW eggs proved to be the most resistant stages to high temperatures. Theseages were usedto determineLT96 for temperatures of between 40 and 47°C for IMM eggs. When compared to LT96sfor IMM pupae, eggs were found to be far more resistant at temperatures of less than 47°C. Resistance of pupae was equal to or greater than eggs at higher temperatures. NOW eggs were found to be much more resistant to high temperature~ than IMM eggs. The LT5o, LT95and LT99for NOW eggs exposed to 40°C were estimated to be about 27, 34, and 38 hours, respectively. Lower developmental thresholds for IMM from laboratory and w!ld-type cultures were found to be similar. For both IMM and NOW, pupae just prior to adult emergence were the most resistant to heat. The lower thresholds for IMM eggs and pupae were 14.8 and 13.9°C, respectively. Exposure of pupae to 46°C for 10 minutes resulted in a decrease in the average number of progeny produced, depending upon pupal age. Fertility of males was more effected by high temperatures than females. These results are encouraging because they indicate that individual insects that survive treatments will be sterile, which should reduce possible reinfestations and the development of resistance. Initial results from field studies using high temperature treatments combined with night-air recirculation are encouraging. Even though target temperatures were not reached, IMM was completely controlled. Other studies showed that higher temperatures could be obtained using higher air speeds during the treatment.