The susceptibility of a cereal aphid pest and its natural enemies to Deltamethrin

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Abstract
The intrinsic toxicity of deltamethrin to the grain aphid Sitobion avenae (F.) (Hemiptera: Aphididae) and a range of its important natural enemies was determined by laboratory topical bioassay. The natural enemies included polyphagous predators such as Pterostichus melanarius (Illiger), Harpalus rufipes (Degeer), Nebria brevicollis (F.), Agonum dorsale (Pont.), Demetrias atricapillus (L.), Trechus quadristriatus (Schrank), Bembidion obtusum (Serville), and B. lampros (Herbst.) (Coleoptera: Carabidae), Tachyporus hypnorum (F.) (Coleoptera: Staphylinidae) and Erigone atra (Blackwall) (Araneae: Linyphiidae), as well as the aphid‐specific ladybird Coccinella septempunctata (L.) (Coleoptera: Coccinellidae). Dose–response relationships were compared between species by probit analysis and maximum likelihood procedures to determine trends of susceptibility, measured in terms of ng a.i. arthropod−1 and μg a.i. g−1 body weight. The range of LD50 values varied between 0.8 and 232 ng arthropod−1 and 0.76 and 66.17 μg g−1 body weight for the species tested. The linyphiid spider E. atra (♀) was the most intrinsically susceptible species and had the narrowest tolerance distribution of the predators tested, whereas the small carabid beetle D. atricapillus was the least intrinsically susceptible predator species. There were significant differences in susceptibility between species of different orders, i.e. the Araneae, Hemiptera and Coleoptera. Differences within the Coleoptera were closely related to body weight, with the exception of the carabid beetle D. atricapillus, which seemed to be tolerant to deltamethrin. Knockdown time studies indicated that D. atricapillus had a higher survival rate after being knocked down than other species of predator. Aphid susceptibility per unit body weight was not significantly different from that of the predators. The aphid did, however, demonstrate a broader tolerance distribution than most of the predators, which may be related to its herbivorous nature. The use of laboratory susceptibility data to determine selectivity and to predict pesticide hazard is discussed.