Feeding by Selected Predators on Alfalfa Weevil1Larvae

Twelve species of field-collected arthropod predators suspected of feeding on alfalfa weevil Hypera postica (Gyllenhal) (Coleoptera: Curculionidae) larvae were studied in the laboratory. Most experiments used weevil instars III and IV. In one type of test, weevil larvae were the only prey; the other type permitted a choice of weevil larvae, Lygus spp. nymphs and pea aphid adults Acyrthosiphon pisum (Harris). Hippodamia convergens (Guérin) (larvae and adults), Coccinella transversoguttata (Faldermann) (adults), Nabis spp. (adults), and Chrysopa oculata (Say) (larvae) preferred aphids. In the absence of aphids, the coccinellids were active weevil predators. The spiders Tibellus oblongus (Walckenaer) and Xysticus sp.; Collops vittatus (Say), Collops bipunctatus (Say) and Forficula auricularia Linn. (all adults), appeared to be opportunistic feeders. The latter ranked among the more effective weevil predators. Agulla sp. (adults) ate very few weevil larvae. Instar IV prey were too large for some smaller predators.