Knockdown-Mortality Responses of Six Stored-Product Beetle Species on Different Surfaces Treated With Thiamethoxam, Using a Standardized Lethality Index

Bioassays were conducted to evaluate the effectiveness of thiamethoxam in different surfaces, against six stored-grain insects, Sitophilus granarius (L.) (Coleoptera: Curculionidae), Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), and Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). Six different surfaces (concrete, plywood, galvanized steel, linen, plastic, and ceramic tile) treated with thiamethoxam at 0.05 and 0.1 mg/cm2 were used as substrate for adult exposure. Knockdown was recorded after 1, 3, and 7 d of exposure to the treated surface, in order to calculate a Standardized Lethality Index (SLI). Knockdown counts were ranked from ‘0’ to ‘4’, with ‘0’ representing adult insects ‘moved generally’ and ‘4’ representing dead insects. Based on the results, insect knockdown seems leading to mortality than to recovery and the SLI ranking of the target species according to their susceptibility to thiamethoxam showed that S. granarius being more susceptible and decreasing susceptibility in an order of S. oryzae > T. castaneum ≥ O. surinamenis ≥ C. ferrugineus ≥ T. confusum. In general, among the surfaces, thiamethoxam efficacy was lower on linen, wooden, and concrete surfaces, as compared to metallic and plastic surfaces. Nevertheless, at the end of 7-d exposure, all surfaces equally affected thiamethoxam toxicity.

Attractiveness of Male and Female Adults of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) to Conspecifics With and Without Grain

Whether stored-grain insects can communicate with each other inside stored-grain bulks is an important question for the development of pest management programs. Movements of the individual adults of Cryptolestes ferrugineus towards caged adult(s), in the presence or absence of wheat, were studied inside an apparatus (10 cm length), using an infrared camera. The numbers of the caged adults were 1, 20, or 50 of females or males, and 100 or 200 mixed-sex adults. Without grain, both males and females moved towards the caged single male, but not the caged single female. With grain, neither males nor females moved towards the caged single male or female. When 50 males were added to the cage, females did move significantly towards the caged males. There were trends for introduced males and females to move towards caged males at higher densities.

Preparation, Characterization and Biological Efficacy of Eucalyptus Oil Nanoemulsion against the Stored Grain Insects

Nanotechnology has enormous potential for developing alternative pest control strategies and reducing the risk of insecticide molecules. The present study aimed to develop a stable nanoemulsion (NE) of eucalyptus oil (EO) by the spontaneous emulsification method and evaluate its insecticidal and repellent effect against Sitophilus oryzae (L.), Rhizopertha dominica (F.) and Tribolium-castaneum (Herbst.). The prepared nanoemulsion formulation having a small particle size 8.57 nm with polydispersity index (PDI) 0.28. The study of the stability and physicochemical properties showed that the prepared formulation had good physical stability without any change in the macroscopic parameters. In addition, results showed that theinsecticidal activity of the prepared NE was higher than the original EO against the three tested insect speciesand the mortality increased with increasing concentrations and extending of exposure time. The contact toxicity of NE film revealed that, adults of R. dominica was more susceptible to all treatments followed by S. oryzae adults, while adults of T. castaneum was the least susceptible one, however, adults of S. oryzae was more susceptible followed by T. castaneum adults while, adults of R. dominica was the least susceptible one according to the fumigant toxicity and repellency. Our results suggested that the prepared formulation may be used in an integrated pest managementprogramfor controlling stored grain insects.