Abstract
The small brown planthopper [Laodelphax striatellus (Fallén) (Hemiptera, Delphacidae)] is one of the most destructive insect pests of rice and has developed strong resistance to several kinds of chemical insecticides. Triflumezopyrim, a novel mesoionic insecticide developed by Corteva Agriscience (formerly DuPont Crop Protection), has efficient biological activity in controlling sucking insects, such as the planthopper. However, the effects of triflumezopyrim on the growth and reproduction of L. striatellus have not been reported. In this study, an F5 generation was obtained by conducting five rounds of insecticide screening on a sensitive L. striatellus strain (F0 generation). An age-stage life table procedure was used to evaluate the effects of a sublethal concentration (LC50) of triflumezopyrim on the biological parameters of L. striatellus. Compared with those of the F0 generation, the intrinsic rate of increase (r), the finite rate (λ), and the net reproductive rate (R0) of the F5 generation were significantly decreased; nevertheless, the average duration of life (T) was not significantly affected. The results of detoxification enzyme activity assays indicated that the glutathione S-transferase and cytochrome P450 monooxygenase (P450) activities in the F5 generation were significantly higher than those in the F0 generation. The contents of vitellogenin (Vg) and vitellogenin receptor (VgR) were also detected, and the results indicated that the contents of Vg and VgR in the F5 generation were significantly decreased compared to those in the F0 generation. Furthermore, we detected the relative expression of ecdysone receptor (EcR), Vg, and VgR in the F0 and F5 generations and found that the relative expression levels of Vg and VgR in the F5 generation female adults were obviously lower than those in the F0 generation (P < 0.05), whereas the relative expression of EcR was slightly increased, although the difference was not significant (P > 0.05). Based on these results, a sublethal concentration (median lethal concentration, LC50) of triflumezopyrim may inhibit the generational growth and reproduction of L. striatellus. Moreover, our results may provide a reference for further studies of the suitability and resistance mechanisms of L. striatellus subjected to a sublethal dose of triflumezopyrim.
Highlights
The small brown planthopper [Laodelphax striatellus (Fallén) (Hemiptera: Delphacidae)] is one of the most destructive insect pests of rice; its adults and nymphs feed directly on rice and spread viral diseases, such as rice blackstreaked dwarf disease (Kisimoto, 1967; Yin et al, 2013)
To understand the changes in the susceptibility of L. striatellus under the screening pressure of triflumezopyrim, we used the rice seedling dipping method to evaluate the toxicity of triflumezopyrim and found that the LC50 values of triflumezopyrim on 3rd-instar nymphs of the F0 and F4
We found that the developmental stage of the F5 generation was not greatly affected, and the values of T, adult preoviposition period (APOP), and total preoviposition period (TPOP) did not change significantly, which was inconsistent with the findings of some previous reports
Summary
The small brown planthopper [Laodelphax striatellus (Fallén) (Hemiptera: Delphacidae)] is one of the most destructive insect pests of rice; its adults and nymphs feed directly on rice and spread viral diseases, such as rice blackstreaked dwarf disease (Kisimoto, 1967; Yin et al, 2013). The biochemical and physiological action of this novel insecticide involves its binding to the orthosteric site of the nicotinic acetylcholine receptor by competitive binding, making the insects lethargic and poisoned, which was highly effective for controlling both imidacloprid-susceptible and imidacloprid-resistant planthopper populations in Malaysia (Cordova et al, 2016). The occurrence of resistance is closely related to the sublethal effects of pesticides on insects and the changes in detoxification enzymes in insects (Ma et al, 2019; Meng et al, 2019a,b). Sublethal effects are manifested mainly in the growth and development of insect individuals and their offspring, feeding behavior, mating and reproduction, oviposition, egg hatching rate, and population growth (RamirezRomero et al, 2007). The expression of the EcR, Vg, and VgR genes has a significant influence on insect growth and reproduction
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