In some herbivorous insect species, egg size is larger on low-quality hosts than on high-quality hosts and may be related to the prospect that larger offspring are more likely to survive on a poor host. Sizes of eggs laid by pollen beetles [Meligethes aeneus Fab. (Coleoptera: Nitidulidae)] were examined with insects confined on one of two different host plants that had previously shown differences in adult preference and larval performance. Individual females were also exposed sequentially to both the low-quality host (Sinapis alba L.) and the high-quality host (Brassica napus L.) and the size of their eggs was determined. Pollen beetles laid shorter eggs on low-quality hosts both for different females on different host plants and for the same individuals on different host plants, in contrast to the prediction that low-quality hosts would receive larger eggs than high-quality hosts. Previously, egg production rate was shown to be reduced when pollen beetles are exposed to low-quality hosts and it is suggested that oogenesis is incomplete, resulting in shorter eggs. The possibility that this is related to antibiosis on S. alba is discussed.
Two-spotted spider mite, Tetranychus urticae Koch (Tetranychidae: Acariformes), is one of the most important agricultural pests in the world. Their populations have a tendency of rapidly developing resistance to acaricides, making it necessary to have a variety of active ingredients for sustainable chemical control of this pest. We investigated acaricidal properties of a relatively new insecticide spirotetramat using its commercial formulation, Movento Energy. Spirotetramat applied at concentrations equivalent to the field rates of 78 and 90 g ai/ha had a strong negative effect on the survival of the treated T. urticae, with ca. 95% of females and ca. 65% of males dying after the treatment. Spirotetramat appeared to interfere with female reproductive system. Many of the dead treated females had eggs stuck in the oviduct and protruding from their bodies. Surviving treated females did not lay eggs. Furthermore, untreated females that mated with treated males did not produce female offspring and displayed the symptoms of spirotetramat poisoning. Toxic effects continued manifesting themselves after female mites were transferred from treated onto untreated plant culture. Contrary to previous studies, contact toxicity was also detected. None of the treated immature stages survived to adulthood. Based on these results, spirotetramat may be a good option for integrated pest management in crops that are simultaneously affected by sucking insects and spider mites and in pesticide rotation sequences that are a part of integrated resistance management programs.
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