The Effect of Acclimation to Sublethal Temperature on Subsequent Susceptibility of Sitophilus zeamais Mostchulsky (Coleoptera: Curculionidae) to High Temperatures

Transcript-Level Analysis in Combination with Real-Time PCR Elucidates Heat Adaptation Mechanism of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) Larvae

Tribolium castaneum (Herbst) ranks as one of the most prevalent insects in food processing and storage facilities worldwide. Heat treatment has been revisited to disinfest food processing and storage facilities due to increasingly strict regulation on chemicals. The effect of acclimation of T. castaneum larvae to sublethal high temperatures of 36 and 42℃ for 10 h on their heat adaptation was investigated, and transcript-level analysis combinating with real-time PCR (RT-qPCR) was applied for elucidating the heat adaptation mechanism of T. castaneum larvae. Short-term sublethal high temperature acclimation could greatly enhance the thermal adaptability in T. castaneum larvae. In total, 575, 875, and 1017 differentially expressed genes (DEGs) were, respectively, determined in comparisons between the 28 and 36℃ treatments, the 28 and 42℃ treatments, and the 36 and 42℃ treatments. Fifty-three and 96 genes were commonly up- and down-regulated in both the 36 and 42℃ treatments relative to 28℃, respectively. The results of RT-qPCR analysis further confirmed the RNA-seq analysis. The current results are in favor of enhancing the insecticidal effectiveness of extreme high temperature treatment and elucidating the heat adaptation mechanism in T. castaneum larvae.

Multigenerational heat acclimation increases thermal tolerance and expression levels of Hsp70 and Hsp90 in the rice leaf folder larvae

Physiological response and acclimation to thermal stress is a key strategy of insects to cope with changing climate. The underlying mechanism of heat acclimation in insects is still unclear. Here, the heat selection and transcript level response in the larvae of the rice leaf folder Cnaphalocrocis medinalis Güenée, a serious pest of rice in summer, were studied. The survival and fecundity of larvae during multigenerational heat selection at 39 °C were examined, and heat tolerance and mRNA expression of heat shock protein 70 (Hsp70) and 90 (Hsp90) were examined under heat stress. The results showed that survival and fecundity of larvae increased notably and then kept constant after two or three generations of heat selection. Heat selection improved thermal tolerance of larvae. The Hsp70 mRNA expression of the 3rd-instar larvae increased in all five generations of heat selection, but Hsp90 increased only in the first two generations. The response of Hsp70 to 39 °C heat treatment in the larvae kept at 27 °C was different from the larvae exposed to the conditioning heat treatments, but the response of Hsp 90 was similar. Moreover, the Hsp70 and Hsp90 mRNA expression levels were significantly higher in the heat-acclimated larvae than that in the unacclimated larvae at a comparable duration of exposure to 37 and 41 °C. Selection at a high temperature across multiple generations led larvae to heat acclimation, and Hsp70 and Hsp90 were involved in this acclimation process.

Effects of Low Pressure Treatment on the Mortality of Different Life Stages of Indianmeal moth (Plodia interpunctella) and the Quality of Dried Chinese Jujube

Low pressure technology is a potential non-chemical method to control insects in agriculture products. The purpose of this study was to determine the tolerance of different life stages of indianmeal moth (Plodia interpunctella) to low pressure and to validate the mortality of P. interpunctella when infesting Chinese jujube (Zizyphus jujuba Miller) using a low pressure system. Results showed that larvae were the most tolerant life stage of P. interpunctella, with a minimum exposure time of 41.4 h at 1.3 kPa and 25 °C to obtain 100% mortality. Pupae were the most susceptible life stage, with a lethal time of 12 h under the above low pressure conditions. The survival ratio of P. interpunctella in jujube decreased with increasing exposure time and reached 0% when the jujubes with P. interpunctella larvae were exposed to low-pressure treatment for 41.6 h at 1.3 kPa and 25 °C. Although the color, moisture, soluble solid, and vitamin C contents were slightly changed, there was no significant quality difference in these factors between control and treated jujubes. The information provided by this study is useful in developing effective non-chemical low-pressure treatments for disinfesting agricultural products.

Effects of High Temperatures on the Mortality of Stegobium paniceum (L.) (Coleoptera: Anobiidae)

As an alternative to chemical fumigants, heat treatment has been a widely used physical method to successfully control stored-product insects in empty grain storage and food processing facilities. The drugstore beetle, Stegobium paniceum (L.) (Coleoptera: Anobiidae) is one of the most destructive stored-product insects in the world. The mortality of the eggs, larvae, pupae, and adults of S. paniceum was investigated when exposed to 43, 47, 51, and 55°C for different time intervals. The mortality rate of the S. paniceum eggs, larvae, pupae, and adults was found to significantly increase with increased exposure time and temperature, and the pupae were the most heat-tolerant stage. The mortality rate of the S. paniceum pupae was <43.3%, while the mortality rate of the S. paniceum eggs, larvae, and adults achieved nearly 100.0% when they were exposed to 43, 47, 51, and 55°C for 6 h, 17.5 min, 120 s, and 30 s, respectively. The current results favor designing a heat treatment protocol to successfully disinfest S. paniceum in practice.

Influence of acclimation to sublethal temperature on heat tolerance of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) exposed to 50°C

Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is a serious pest of stored agricultural products and one of the most common insects found in grain storage and food processing facilities. Heat treatment has been revisited to control stored-product insects as a potential alternative to methyl bromide for disinfesting mills and food-processing facilities. The influence of acclimation of T. castaneum adults, pupae, larvae, and eggs to sublethal temperatures of 36, and 42°C on their subsequent susceptibility to lethal temperature of 50°C was respectively investigated. The acclimation of T. castaneum eggs, larvae, pupae, and adults to 36, and 42°C significantly decreased their subsequent susceptibility to lethal high temperature of 50°C. The influence of acclimation to 42°C was significantly greater than that of acclimation to 36°C. The most influential acclimation times at 42°C for mortality of T. castaneum eggs, larvae, pupae, and adults were 15, 5, 5, and 5 h, respectively, and their corresponding mortality were 41.24, 5.59, 20.19, and 4.48%, compared to 100% mortality of T. castaneum eggs, larvae, pupae, and adults without acclimation when exposed to 50°C for 35 min, respectively. The present results have important implications for developing successful heat treatment protocols to control T. castaneum, improving disinfestation effectiveness of heat treatment and understanding insect response to high temperatures.