The cabbage aphid, Brevicoryne brassicae (L.), is one of the major insect pests of cole crops in Iran. In most instances outbreaks are normally kept under control by application of insecticides. In this study, the sublethal effects (LC30) of three insecticides, acetamiprid, buprofezin, and thiamethoxam-lambda cyhalothrin, (TLC) were evaluated on the population growth rate of the progeny of insecticide-treated cabbage aphid adults. The age-stage, two-sex life table method was used to analyze the collected data. The results indicated that the insecticide applications affected the duration of the preadult period, their survival, reproduction, life span/longevity, and consequently, the population growth rate of the F1 generation. The indicators of the greatest sublethal effects were noted in the progeny of the TLC-treated adults. These included the lowest net reproductive rate (R0), intrinsic rate of increase (r), finite rate of increase (λ), and the longest mean generation time (T). The highest values of r, λ, R, and the lowest value of T occurred in the control group followed by, in order, the acetamiprid and buprofezin groups. These research findings will be useful in the development and implementation of future aphid management programs.
Plutella xylostella has become particularly notorious for its resistance to various insecticides. The toxicities of abamectin, hexaflumuron and indoxacarb to third instar larvae of the pest were assayed using the leaf-dipping method. The results showed that abamectin and indoxacarb with the lowest LC50 values exhibited stronger toxicity to larvae than hexaflumuron. To determine the synergism of PBO, DEM, DEF and TPP on the toxicity of tested insecticides and demonstrating possible biochemical mechanisms, an abamectin-, a hexaflumuron-and an indoxacarb-resistant strain of P. xylostella were selected under laboratory conditions. After 10 generations of selection, the selected strains developed 14.21, 7.08, and 32.36-fold higher resistance to these insecticides, respectively. Abamectin resistance in abamectin-selected strain was suppressed with the synergists such as DEM and PBO, suggesting the involvement of monooxygeneses and glutathione S-transferase in the development of resistance in P. xylostella. Treatment with PBO and DEF significantly decreased the toxicity of hexaflumuron in the hexaflumuron-selected strain. Also, in indoxacarb-selected strain, the maximum synergism was occurred using PBO and DEF, followed by DEM and TPP. Hexaflumuron and indoxacarb synergism studies indicated in hexaflumuron resistance, monooxygenases and esterases, and in indoxacarb resistance, monooxygenases, esterases and glutathione S-transferae may be involved in the resistance mechanisms
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