Biogenetic cantharidin is a promising leading compound to manage insecticide resistance of Mythimna separata (Lepidoptera: Noctuidae).

Cantharidin (CTD) is a natural toxin with effective toxicity to lepidopteran pests. Nevertheless, little information is available on whether pests develop resistance to CTD. After being exposed to CTD (50 mg/L to 90 mg/L) or 10 generations, the resistance ratio of laboratory selected cantharidin-resistant Mythimna separata (Cantharidin-SEL) strain was only elevated 1.95-fold. Meanwhile, the developmental time for M. separata was prolonged (delayed1.65 in males and 1.84 days in females). The reported CTD target, the serine/threonine phosphatases (PSPs), have not been shown significant activity variation during the whole process of CTD-treatment. The activity of detoxification enzymes (cytochrome monooxygenase P450, glutathione-S-transferase (GST) and carboxylesterase) were affected by CTD selection, but this change was not mathematically significant. More importantly, no obvious cross-resistance with other commonly used insecticides was observed in the M. separata population treated with CTD for 10 generations (resistance ratios were all lower 2.5). Overall, M. separata is unlikely to produce target-site insensitivity resistance, metabolic resistance to CTD. Meanwhile, cantharidin-SEL is not prone to develop cross-resistance with other insecticides. These results indicate that CTD is a promising biogenetic lead compound which can be applied in the resistance management on M. separata.

Biological Evaluation of Endothall, a Dicarboxylic Acid Analog of Norcantharidin, and Cantharidin on Oriental Leafworm, Spodoptera litura (Lepidoptera: Noctuidae).

Cantharidin is a highly potent toxin produced by insects belonging to the order Coleoptera and family Meloidae. The insecticidal activity of cantharidin against different orders of insects has been well documented. Although it is highly effective, its extraction and synthesis is very tedious. Consequently, much work is underway to synthesize the bioactive analogs of norcantharidin and study their relative structures. In this study, we investigate the acute and chronic toxicological effects of cantharidin and endothall, an analog of norcantharidin, using an age-stage-based two-sex life table methodology. Results reveal the acute toxicity of these compounds to Spodoptera litura Fabricius (Lepidoptera: Noctuidae), with the LC50 of cantharidin being 2.10 and endothall being 3.72 ppm, after 72 h posttreatment. Although both the compounds negatively affected the intrinsic rate of population increase (r), finite rate of increase (λ), net reproduction rate (R0), mean generation time (T), doubling time (DT), relative fitness (Rf), biotic potential, and longevity, cantharidin was slightly more effective. Among the reproductive parameters, fecundity was severely affected by cantharidin, which reduced offspring to 42 compared to 528 per female in the control cohort. Both cantharidin and endothall caused similar physiological changes such as weight reduction, wing malformation, and pupal deformities. These findings demonstrate that both cantharidin and endothall are highly toxic to S. litura, particularly in their chronic effects on population parameters. This will help us to understand the biological and ecological interactions in agricultural cropping systems and how their application will modify insect herbivory.

Toxicity and Sublethal Effects of Cantharidin on Musca domestica (Diptera: Muscidae).

The house fly, Musca domestica L. (Diptera: Muscidae), is a major pest of medical and veterinary importance all over the world. Management efforts for house flies are usually compromised owing to their resistance to many groups of conventional insecticides. Cantharidin, a natural toxin produced by meloid beetles, is a biopesticide with a reported toxicity to some insect pests including house flies. However, the effects of cantharidin on biological and fitness parameters of house flies have not yet been investigated. In the present study, we investigated the toxicity and sublethal effects of cantharidin on biological parameters of house flies for two consecutive generations. The results revealed that the values of LC50, LC25, LC10, and LC2 against house flies were to be 2.45, 1.23, 0.66, and 0.30 mg/liter, respectively. Sublethal effects of these concentrations on the development and reproduction parameters of house flies revealed that cantharidin reduced population growth by affecting pupation rate, adult emergence, and by lengthening developmental time. The female ratio, fecundity, egg hatching, and survival of adult flies were significantly reduced at LC2, LC10, LC25, and LC50 of cantharidin when compared with the control group. Furthermore, the increase in concentration of cantharidin had a significant effect on reducing the mean values of mean relative growth rate, net reproductive rate (Ro), intrinsic rate of natural increase (rm), and biotic potential (bp). In conclusion, the results of this study revealed the toxicity of cantharidin against house flies and the adverse effects of sublethal concentrations on biological parameters which may have positive implications for effective management of house flies.