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Insects damage grain during post-harvest storage. Grain loss during storage is a serious problem, especially in less-developed countries. In this study, a gaseous ClO2 treatment was applied to four different insect species known to damage stored grains: Sitophilus zeamais (Motschulsky), Trogoderma granarium (Everts), Callosobruchus chinensis (Linnaeus), and Tribolium castaneum (Herbst). Different insect species showed different sensitivities to the same ClO2 fumigation conditions. The 100 ppm treatment level with 24 h exposure is effective to controlling S. zeamais, T. granarium, and C. chinensis. However, to control T. castaneum, a higher concentration of the ClO2 gas or increased exposure time is needed. The 200 ppm treatment level with 48 h exposure is effective to controlling T. castaneum.

Polyunsaturated fatty acids usually undergo lipid peroxidation induced by reactive oxygen species (ROS). Calcium-independent cellular phospholipase A2 (iPLA2) can maintain fatty acid compositions in phospholipids depending on physiological conditions. An insect iPLA2 (Pi-iPLA2) was predicted from the transciptome of the Indianmeal moth, Plodia interpunctella. It encodes 835 amino acids. It possesses five ankyrin repeats in the N terminal and patatin lipase domain in the C terminal. Pi-iPLA2 was expressed in all developmental stages of the Indianmeal moth. In the larval stage, it was expressed in all tissues tested. RNA interference (RNAi) specific to Pi-iPLA2 was performed using specific double-stranded RNA (dsRNA). It resulted in almost 70% of reduction in gene expression. Under such RNAi condition, P. interpunctella exhibited significant accumulation of lipid peroxidation based on the amount of malondialdehyde. RNAi of Pi-PLA2 expression also impaired cellular immune response of P. interpunctella. Chlorine dioxide (ClO2), an insecticidal agent by generating ROS, increased lipid peroxidation in a dose-dependent manner. However, the addition of vitamin E (an antioxidant) reduced the formation of lipid peroxidation. ClO2 treatment significantly reduced expression of Pi-iPLA2 but increased lipid peroxidation in larval fat body of P. interpunctella. Furthermore, larvae treated with dsRNA specific to Pi-iPLA2 were significantly susceptible to ClO2 treatment. These results suggest that Pi-iPLA2 plays a crucial role in repairing damaged fatty acids from phospholipids. Our results also suggest that ClO2 can elevate lipid peroxidation through inhibiting Pi-iPLA2 expression in addition to direct ROS production.

The Indian meal moth, Plodia interpunctella, causes massive damage to stored grains and processed foods. Heat treatment has been widely used to control insect pests infesting stored grains. However, heat treatment may result in unsatisfactory control owing to heat tolerance of target insects. This study quantified the heat tolerance and analyzed its induction in P. interpunctella. Susceptibility of P. interpunctella to different high temperatures was assessed in all developmental stages. Heat treatment at 44 °C for 1 h caused significant mortalities to all developmental stages, with late-instar larvae exhibiting the highest tolerance. However, the survivorship to heat treatment was significantly increased by pre-exposure to 37 °C for 30 min. The induction of heat tolerance was accompanied by upregulation of two heat shock proteins of Hsc70 and Hsp90. Trehalose and glycerol concentrations in the hemolymph also increased after pre-exposure to 37 °C for 30 min. RNA interference (RNAi) by specific double-stranded RNAs effectively suppressed the inducible expressions of both Hsc70 and Hsp90 in response to 37 °C for 30 min. Either RNAi of Hsc70 or Hsp90 significantly impaired the heat tolerance induction of P. interpunctella. These results suggest that the induction of heat tolerance in P. interpunctella involves the upregulation of these heat shock proteins and hemolymph polyol levels.

Plodia interpunctella and Sitophilus zeamais are among the most destructive insect pests of stored processed food products. The use of natural materials rather than conventional pesticides to control these pests is a promising alternative to conventional neurotoxic insecticides. In this study, we tested organic extracts from 13 species of plants; most showed different effects on S. zeamais and P. interpunctella. Eleven of the extracts had repellent effects on S. zeamais but either an attractant effect or no effect on P. interpunctella. These results suggested that different species of insects have different reactions to plant extracts, and such extracts may have applications as storage products to prevent infestation by both P. interpunctella and S. zeamais.

Gaseous chlorine dioxide (ClO2) was applied to fumigate larvae and adult stages of Plodia interpunctella (Hubner) (Lepidoptera: Pyralidae) and Sitophilus zeamais (Motschulsky) in rice grain bags stored in a grain storage room. It was confirmed that the fumigation efficiency varied depending on the storage position and insect life stage and species. The fumigation effect was the highest on the surface of the grain bag and lowest on the middle of the outer position on the grain storage bag. The mortality of adult P. interpunctella, 5 days after ClO2 fumigation, reached 100% regardless of their position, whereas that of the larva P. interpunctella and adult S. zeamais varied depending on their positions. The mortalities in the outer portions of the grain bag were the highest, followed by that at the top of the grain bag. The ClO2 residue of treated rice were lower than that accepted by international standards. To achieve fumigation effectiveness which similar with lab scale experiment, more researches which are related to infiltration or circulation of gaseous ClO2 are needed.

A novel fumigant, chlorine dioxide (ClO2) is a commercial bleaching and disinfection agent. Recent study indicates its insecticidal activity. However, its mode of action to kill insects is yet to be understood. This study set up a hypothesis that an oxidative stress induced by ClO2 is a main factor to kill insects. The Indian meal moth, Plodia interpunctella, is a lepidopteran insect pest infesting various stored grains. Larvae of P. interpunctella were highly susceptible to ClO2 gas, which exhibited an acute toxicity. Physiological damages by ClO2 were observed in hemocytes. At high doses, the larvae of P. interpunctella suffered significant reduction of total hemocytes. At low doses, ClO2 impaired hemocyte behaviors. The cytotoxicity of ClO2 was further analyzed using two insect cell lines, where Sf9 cells were more susceptible to ClO2 than High Five cells. The cells treated with ClO2 produced reactive oxygen species (ROS). The produced ROS amounts increased with an increase of the treated ClO2 amount. However, the addition of an antioxidant, vitamin E, significantly attenuated the cytotoxicity of ClO2 in a dose-dependent manner. To support the oxidative stress induced by ClO2, two antioxidant genes (superoxide dismutase (SOD) and thioredoxin-peroxidase (Tpx)) were identified from P. interpunctella EST library using ortholog sequences of Bombyx mori. Both SOD and Tpx were expressed in larvae of P. interpunctella especially under oxidative stress induced by bacterial challenge. Exposure to ClO2 gas significantly induced the gene expression of both SOD and Tpx. RNA interference of SOD or Tpx using specific double stranded RNAs significantly enhanced the lethality of P. interpunctella to ClO2 gas treatment as well as to the bacterial challenge. These results suggest that ClO2 induces the production of insecticidal ROS, which results in a fatal oxidative stress in P. interpunctella.

Polyunsaturated fatty acids usually undergo lipid peroxidation induced by reactive oxygen species (ROS). Calcium-independent cellular phospholipase A

This paper presents sequential sampling plans for evaluating the pest density based on complete counts from probe in a rice storage warehouse. Both maize weevil and Indian meal moth population showed negative binomial dispersion patterns in brown rice storage. For cost-effective monitoring and action decision making system, sequential sampling plans by using the sequential probability ratio test (SPRT) were developed for the maize weevil and Indian meal moth in warehouses with 0.8 M/T storage bags. The action threshold for the two insect pests was estimated to 5 insects per kg, which was projected by a matrix model. The results show that, using SPRT methods, managers can make decisions using only 20 probe with a minimum risk of incorrect assessment.

The biology of indian meal moth and maize weevil on the trehalose gene introduced rice (var `Nakdong`) (T-Nakdong) was compared to that on the rice without gene introduction (Nakdong) at . Development of the both two insects was significantly delayed; on T-Nakdong, the developmental periods of female moth and weevil were , respectively. Whereas those on Nakdong were , respectively. Net reproduction rate of Indian meal moth on T-Nakdong was significantly lower than that on Nakdong , due to the lower emergence rate . The life table statistics of maize weevil on T-Nakdong was estimated to be similar to those on Nakdong. The delayed development of T-Nakdong suggested that the factor for development of the insects could be changed by the introduction of trehalose gene into the rice variety.

Influences of the spatial distribution of resource patches on the host-parasitoid system (brown rice patch - rice weevil - Anisopteromalus calandrae ) dynamics and stability in patchy environment were studied with a biological model system. When the 40 resource patches (each containing 5 g of brown rice) were contagiously distributed among 453 empty patches, the host population increased logistically and then fluctuated at an equilibrium level about 5,000. However, when the resource patches were randomly distributed, the host population showed a cyclical fluctuations in the range from 532 to 7089 with significant delayed density-dependence. Distribution of resource patches affected the distribution of hosts among resource patches, which could be a reason for the different features of population dynamics in the two system. In both resource patch distribution systems, the interactions between host and parasitoid populations could be persistent and maintained at an equilibrium level with oscillatory damping. The equilibrium level in each system was far below than that in the system without parasitoid, suggesting that the parasitoid did regulate the host population. However, overall mortality of host due to the parasitism was host density-independent in the contagious system or inversely host density-dependent in the random system. Therefore, the regulation seemed due not to overall host density-dependent parasitism, but rather to the indirect effect of the parasitoid leading the host population to be highly aggregating to some resource patches, which, in turn, resulted in stronger intraspecific competition. The key factor in regulation of the host population was estimated to be intraspecific competition in the contagious resource patch system, whereas it was parasitism in the random patch system. The persistence and stability of host-parasitoid population interaction, the role of parasitoid in the interaction and the resulting equilibrium level were discussed with reference to the resource patch distribution.

Biological control of rice weevil, Sitophilus oryzae (L.), and Indianmeal moth, Plodia interpunctella (Hubner), by their parasitoids Anisopteromalus calandrae (Howard) and Bracon hebetor Say was examined while considering the intraspecific competition pattern of the pests. In both experimental and simulation studies, A. calandrae was shown to suppress the rice weevil population, a contest type competitor, regardless of the parasitoid/weevil ratios tested. In contrast, B. hebetor only significantly suppressed the Indianmeal moth, a scramble type competitor, when the parasitoid/moth ratio was >0.05. At ratios lower than 0.05, the role of B. hebetor was negligible, and the correlation coefficients between the number of moths that had emerged and the parasitoid/moth ratio was estimated to be 0.07. The control efficiency of the two parasitoids with respect to the parasitoid/host ratio was estimated using a ratio-response model. To suppress the weevil density to a level that was only 10% of the current density, the ratio was estimated to be 0.02, whereas this value was 0.14 for the Indianmeal moth. However, for the continuous suppression of the Indianmeal moth, periodic and iterative introduction of B. hebetor was required.

The effects of oviposition behavior of Callosobruchus chinensis (L.) on life table statistics of progeny and on attack by the larval ectoparasitoid Anisopteromalus calandrae (Howard) were studied. As the number of eggs per seed increased, larval development time and survival rate decreased. Differences in mortality between treatments was caused largely by competition in the late instars. Life table statistics showed an inverse linear relationship to the number of eggs per seed. Depositing one egg per seed increased progeny production by ≈56% compared with six eggs per seed. The functional response of A. calandrae showed a linear relationship with host density in the range of 1–64 per 100 seeds. The parasitoid searched for its hosts more efficiently when the number of eggs per seed increased from one to four; search rate of the parasitoid based on random search increased from 0.045 ± 0.013 (mean ± SEM) to 0.154 ± 0.025. The results indicate that ovipositing fewer eggs per seed is also a good defense tactic for the weevil against the parasitoids. Whether parasitoids or larval competition selected the oviposition behavior is not yet clear. However, the influence of natural enemies should be studied further to understand the evolutionary process of the weevil's oviposition behavior more precisely.