Abstract
The tomato leaf miner (TLM), Tuta absoluta (Meyrick), is an invasive tomato pest found worldwide. Sustainable control strategies aimed at increasing biological control approaches and decreasing chemical inputs are required, due to the tendency to develop insecticide resistance. In this study, the lethal and sublethal effects of four chemical insecticides (abamectin, indoxacarb, chlorantraniliprole, and spinosad) and the sublethal effects of the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) on a widespread TLM egg parasitoid, Trichogramma brassicae Bezdenko, were estimated. Concentration mortality response bioassays enabled the estimation of lethal concentrations of the tested insecticides for the parasitoids, with chlorantraniliprole having the lowest LC50 and indoxacarb the highest. The LC25 and LC50 of the tested insecticides on the TLM were sprayed on eggs and then offered at three time intervals to the parasitoids. The fertility and other life table parameters of the individuals emerging from the treated eggs were estimated. All of the chemical insecticides, but not the fungus, had harmful effects on T. brassicae. The insecticide applications caused a 3.84–5.17 times reduction in the net reproductive rate (R0) compared with the control. No parameters were affected by spraying the fungus in the 0h treatment, but effects were recorded at 24 and/or 48h, except for the gross reproduction rate (GRR). The value of the intrinsic rate of increase (rm) also decreased to 0.528–0.617 after the insecticide treatments. The doubling time (DT) increased in all treatments compared to the control. Nevertheless, the generation time (T) was only very slightly affected. In addition, in the combination experiments, M. anisopliae showed a remarkable synergism with T. brassicae in controlling TLM eggs. These results indicate that low levels of lethal effects on key biological control agents should be considered in the choice of insecticides to be included in sustainable TLM control packages.
Highlights
The tomato leaf miner (TLM), Tuta absoluta (Meyrick)
The results indicated that chlorantraniliprole had the lowest LC50 value (0.02 mg a.i./l), followed by spinosad, abamectin and indoxacarb (0.14, 0.31 and 1.34 mg a.i./l)
The LC50 value of chlorantraniliprole on T. brassicae was 5.33 times higher than that of the T. absoluta examined in our previous study [72]
Summary
The tomato leaf miner (TLM), Tuta absoluta (Meyrick) The comprehensive review of Han et al [4,5,6] suggests that this pest, due to its ability to adapt to newly invaded areas, high reproduction potential and other traits, can be very harmful for tomatoes in Middle Eastern countries such as Iran. It was first report in Turkey in 2009, and invaded Iran’s fields in 2009, possibly via its borders with Turkey or Iraq [7]
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