Insect populations exist under acute and chronic exposures to lethal and sublethal insecticide concentrations. Among the sublethal effects of insecticides on insects are reductions in life span, development rates, population growth, fertility, fecundity, changes in sex ratio, deformities, changes in behaviour, feeding, searching, and oviposition. These effects may differ depending on the modes of action of insecticides, their doses, and developmental stage of application. This study evaluated the life-history parameters in Musca domestica Linnaeus, 1758 (Diptera:Muscidae) strains that were exposed to two insecticides (fipronil and chlorfenapyr) with different modes of action at sublethal concentrations in each generation up to tenth. Two approaches to each insecticide’s exposure were used in this study, particularly in one approach, only adults M. domestica were exposed to fipronil or chlorfenapyr and in another approach, only larvae were exposed to each insecticide. The susceptibility of adult flies to these insecticides was assessed by resistance ratio based on results of non-choice feeding bioassays. Fipronil exposure at the sublethal concentration in each generation did not affect the susceptibility of adult M. domestica (in the tenth generation) to fipronil. The resistance ratio values revealed tolerance to chlorfenapyr in adults of M. domestica strains that were exposed to this insecticide, independent of the approach used to insecticide exposure. Most of the life-history parameters (such as durations of separate developmental stages, the emergence duration, the adult emergence ratio, the female ratio, and the number of eggs per female per day) of the second, fourth, sixth, eighth, and tenth generations of the insecticide-exposed strains were similar to those of the control strain. At the same time, the sublethal effects of both insecticides fipronil and chlorfenapyr prolonged the larval duration (1.63–2.22 times) and the number of days from egg to adult (1.18–1.39 times) compared to the control strain. Further studies are needed to investigate a possible genetic variability in M. domestica in response to exposure of parental generation to sublethal doses of fipronil and chlorfenapyr.
Toxicological assessment is a mandatory research step in the development of new insecticidal drugs. At the All-Russian Research Institute of Veterinary Entomology and Arachnology, a prototype of the insecticidal bait Mukhnet IF was obtained with an active ingredient content of 0.06% ivermectin and 0.015% fipronil, which showed a highly effective effect against houseflies. This work presents the results of the study of acute oral toxicity of the above agent. For this, male white mice with a live weight of 16-26 g were selected. They were kept on a starvation diet for one day in individual houses with water. The drug was given in mg/kg body weight the next day. A total of 33 doses have been tested, ranging from 100 mg/kg to 40,000 mg/kg. The animals were observed for 14 days. According to the research results, it was revealed that at doses up to 20,000 mg/kg there were no signs of intoxication, but when tested at 25,000 mg/kg in some mice, these signs were noted, and at 30,000, 35,000 and 40,000 mg/kg deaths were recorded 20±10, 45±30 and 60±20%, respectively. It was not possible to test the drug over the last above dose due to incomplete eaten by mice. According to the degree of danger for warm-blooded animals, the drug belongs to the 4th class of low-hazard drugs (average lethal dose of 5000 mg/kg or more) in accordance with the classification of GOST 12.1.007-76. When analyzing the literature data on the toxicological characteristics of preparations containing ivermectin and chlorfenapyr, it was revealed that the insecticidal agent in its acute toxicity for warm-blooded animals is comparable to known analogues.
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