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In addition to direct mortality caused by insecticides, some biological traits of insects may also be affected by sublethal insecticide doses. In this study, we used the age-stage, two-sex life table method to evaluate the sublethal effects of the four synthetic insecticides: abamectin, imidacloprid, diazinon, and pymetrozin as well as the botanical insecticide taken from Calotropis procera (Asclepiadaceae) extract, on eggs of the cotton whitefly, Bemisia tabaci (Hem.: Aleyrodidae). The lowest and highest survival rates and oviposition periods were observed in whiteflies treated by diazinon and imidacloprid, respectively. We found significant differences in the net reproductive rate (R0), the intrinsic rate of increase (r), the finite rate of increase (?), and the gross reproductive rate (GRR) among different insecticides. Altogether, our results showed that pymetrozin and C. procera induced the most sublethal effects, thus they may be suitable candidates for use in integrated pest management programs of B. tabaci.
The resistance of 8 tomato varieties to cotton white fly, Bemisia tabaci (Genn) (Hemiptera: Aleyrodidae), was evaluated in four greenhouse experiments. In the first experiment, we evaluated the attractiveness and preference for oviposition in a free-choice test (randomized blocks, 8 treatments, and 5 replications). In the other experiments, we evaluated the no-choice preference for oviposition (randomized blocks, 4 treatments, and 4 replications). The whitefly egg-adult cycle was monitored using a statistical design in randomized blocks with four replications. The percentage mortality of immature stages was also determined (randomized blocks with four replications). In the free-choice test, the tomato variety Rio Grande was the most attractive to adults, while the variety Cheffalat had the lowest number of adults. Also in this assay, the variety CAL-JN3 presented the lowest number of eggs, while the variety Ergon presented the highest number of eggs. In the no-choice test, the varieties Chef-falat and CAL-JN3 remained resistant. Consequently, for these two varieties non-preference is the oviposition resistance mechanism. The egg-adult cycle varied from 26.02 days (Ergon) to 26.66 days (CAL-JN3). The total mortality varied from 20.52 (Ergon) to 33.97 (CAL-JN3). Considering all the characteristics, the variety CAL-JN3 was the most resistant to B. tabaci among all the tomato varieties studied, while variety Ergon was susceptible.
The resistance of 8 tomato varieties to cotton white fly, Bemisia tabaci (Genn) (Hemiptera: Aleyrodidae), was evaluated in four greenhouse experiments. In the first experiment, we evaluated the attractiveness and preference for oviposition in a free-choice test (randomized blocks, 8 treatments, and 5 replications). In the other experiments, we evaluated the no-choice preference for oviposition (randomized blocks, 4 treatments, and 4 replications). The whitefly egg-adult cycle was monitored using a statistical design in randomized blocks with four replications. The percentage mortality of immature stages was also determined (randomized blocks with four replications). In the free-choice test, the tomato variety Rio Grande was the most attractive to adults, while the variety Cheffalat had the lowest number of adults. Also in this assay, the variety CAL-JN3 presented the lowest number of eggs, while the variety Ergon presented the highest number of eggs. In the no-choice test, the varieties Chef-falat and CAL-JN3 remained resistant. Consequently, for these two varieties non-preference is the oviposition resistance mechanism. The egg-adult cycle varied from 26.02 days (Ergon) to 26.66 days (CAL-JN3). The total mortality varied from 20.52 (Ergon) to 33.97 (CAL-JN3). Considering all the characteristics, the variety CAL-JN3 was the most resistant to B. tabaci among all the tomato varieties studied, while variety Ergon was susceptible.
The granary weevil, Sitophilus granarius (L.), is one of the most important internal feeders of stored grain. Nanotechnology has become one of the most promising new approaches for pest control in recent years. In our screening program, laboratory trials were conducted to determine the effectiveness of silica nanoparticles (SNPs) and zinc nanoparticles (ZNPs) against the larval stage and adults of S. granarius on stored wheat. Nanoparticles of silica and zinc were synthesized through a solvothermal method. They were then used to prepare insecticidal solutions of different concentrations and tested on S. granarius. Silica nanoparticles (SNPs) were found to be highly effective against S. granarius causing 100% mortality after 2 weeks. ZNPs were moderately effective against this pest.
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