Evaluating the combination of Metarhizium anisopliae and an enhanced form of diatomaceous earth (Grain-Guard) for the environmentally friendly control of stored grain pests

Stored grain pests cause great damage to various grain products, and protection against these pests is currently based on synthetic insecticides and fumigants. As a result, these chemicals cause problems, including grain contamination with chemical residues and the development of resistance by insect pests to these chemicals. Therefore, to combat this issue, in the present study, an enhanced form of diatomaceous earth (DE), Grain-Guard, and Metarhizium anisopliae (Metschnikoff) Sorokin (Ascomycota: Sordariomycetes) were evaluated alone and in combination against adults of Liposcelis paeta (Pearman) (Psocoptera: Liposcelididae), Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). M. anisopliae was used at a rate of 1.7 × 10⁴ conidia kg^-1 grain alone as well as with two doses of DE (25 and 50 ppm) on wheat under different exposure time courses (4, 7, and 14 days). It is worth mentioning that the combination of M. anisopliae and DE was highly effective against the adults of L. paeta, C. ferrugineus, R. dominica, and T. castaneum after 14 days of exposure. When DE and M. anisopliae were applied alone, DE showed more effectiveness than fungal conidia. Progeny emergence was decreased when modified DE was applied at a high dose rate with the fungus and suppressed at a low dose. The cadavers of all species in the trials showed a maximum percentage of mycosis, and sporulation (conidia/ml) also showed the same result when the fungus was tested alone, while low mycosis and sporulation were achieved under the application of a mixture with a high dose of modified DE. Our findings indicate the best possible combination of DE (at low dose rates) along with a fungus that might contribute to lowering health and environmental risks.

Efficacy of Entomopathogenic Nematodes Against the Tobacco Cutworm, Spodoptera litura (Lepidoptera: Noctuidae)

Spodoptera litura (F.) is an obnoxious cosmopolitan pest that causes serious damage to different economic crops. Entomopathogenic nematodes (EPN) have the potential to control the S. litura larvae. Fifteen EPN isolates were screened, and Steinernema sp. 64-2, four isolates of S. carpocapsae (Weiser), S. longicaudum (Shen & Wang) X-7, and two isolates of H. indica (Poinar, Karunaka & David) were found to cause higher mortality of the second, third, and fourth instars of S. litura than the other tested isolates, with larval mortality rates > 90% after 48 h of exposure. An exposure rate of 12.5 infective juveniles per larva was enough for S. carpocapsae A24, All, and G-R3a-2 and S. longicaudum X-7 to cause 100% mortality of the second instar, and for S. longicaudum X-7 and H. indica 212-2 to cause 100% mortality of the third instar. Five EPN isolates were tested on their virulence at different temperatures and found that all the five EPN isolates performed well against the S. litura larvae at 25 and 30°C, but were not active at 10 and 15°C. Two S. carpocapsae isolates (All and Mex) were virulent against the S. litura larvae at lower temperatures. The five tested EPN isolates were also found to have the ability to infect and kill the pupae of S. litura in the laboratory. The present study further proves that EPN are effective at controlling S. litura, which may partially substitute the use of chemical insecticides, thus reduce the overuse of chemical insecticides.

Comparative analysis of the demographic parameters of seven spotted ladybird beetle (Coleoptera: Coccinellidae) reared on various host aphid species

Background

The demographic parameters of the predacious seven spotted ladybird beetle Coccinella septempunctata Linnaeus (Coleoptera: Coccinellidae) reared on the following four host aphid species were compared: Rhopalosiphum padi Linnaeus (Hemiptera: Aphididae), Rhopalosiphum maidis Fitch (Hemiptera: Aphididae), Sitobion avenae Fabricius (Hemiptera: Aphididae), and Schizaphis graminum Rondani (Hemiptera: Aphididae).

Methods

The developmental period, fecundity, adult preoviposition period, total preoviposition period and population parameters were evaluated based on the two-sex age-stage life table. The duration of the developmental stages and the population parameters were calculated with the TWOSEX-MSChart program, whereas population size was projected based on the two-sex age-stage life table data with the TIMING-MSChart program.

Results

The intrinsic rate of increase (r) was the highest in the R. padi predators (0.1946 per day), followed by the S. graminum (0.1435 per day), S. avenae (0.1400 per day), and R. maidis (0.1180 per day) predators. The differences in the net reproductive rate (R ₀) and the finite rate of increase (λ) when C. septempunctata was reared on the four aphid species were consistent with the r values. This trend was reversed for the mean generation time (T), which ranged from 29.02 days for the lady beetles reared on R. padi to 39.75 days for the lady beetles reared on R. maidis. Interestingly, R. padi was the most suitable host, while the congeneric R. maidis was the least suitable. The results of this study may be useful for future investigations regarding the ecological effects of predatory species and the mass-production of C. septempunctata in the laboratory for an augmentative release of an aphid predator.

Association of detoxification enzymes with butene-fipronil in larvae and adults of Drosophila melanogaster

Insecticide resistance is a major challenge in successful insect pest control as the insects have the ability to develop resistance to various widely used insecticides. Butene-fipronil is a novel compound with high toxicity to insects and less toxicity to the non-target organisms. In the present study, the effect of butene-fipronil alone and in combination with three enzyme inhibitors, piperonyl butoxide (PBO), diethyl maleate (DEM), and triphenyl phosphate (TPP), was carried out on larvae and adults of Drosophilia melanogaster. Our results indicated that the co-toxicity indices of butene-fipronil + PBO, butene-fipronil + TPP, and butene-fipronil + DEM mixtures were 437.3, 335.0, and 210.3, respectively, in the second-instar larvae, while 186.6, 256.2, and 238.5, respectively, in the adults, indicating synergistic effects. Interestingly, butene-fipronil increased the expression of CYP28A5 in the larvae; CYP9F2, CYP304A1, CYP28A5, and CYP318A1 in the female adults; and CYP303A1 and CYP28A5 in the male adults. Furthermore, high-level expression of Est-7 was observed in the female adults compared to larvae and male adults. Our results suggest that there is no difference in butene-fipronil metabolism in larvae and male and female adults of D. melanogaster.

Assessment of toxicity and potential risk of butene-fipronil using Drosophila melanogaster, in comparison to nine conventional insecticides

The toxicities of butene-fipronil to Drosophila melanogaster were evaluated, in comparison to nine conventional insecticides. According to the mean LD50 values of the larvae from CS, w(1118) and Oregan strains, butene-fipronil,abamectin, spinosad and chlorpyrifos exhibited high levels of toxicity. Imidacloprid, α-cypermethrin and clothianidin showed middle levels of toxicity. And acephate,methomyl and acetamiprid had low levels of toxicity. To the adults, butene-fipronil, α-cypermethrin, spinosad, and chlorpyrifos were relatively more toxic, whereas acephate,methomyl, acetamiprid, imidacloprid, clothianidin and abamectin were relatively less toxic. Butene-fipronil and abamectin were more toxic to larvae. In contrast, spinosad,a-cypermethrin, and clothianidin were more toxic to adults.Moreover, the toxic risk assessment using a risk quotient value revealed that butene-fipronil was safe to D. melanogaster adults. Thus, our results suggested that butene-fipronil is harmful to D. melanogaster larvae, but it is relatively safe to the adults.