Survival of some aphid (Hemiptera: Aphididae) predators with special reference to their parasites in England

Abstract

AbstractStudies in southern England on aphids in cereals and adjacent wasteland included observations on the survival of aphid-specific predators (Coccinel-lidae and Syrphidae) and the more polyphagous Chrysoperla carnea (Steph.), with particular reference to their parasites. Counts were made of all the predator stages found on samples of shoots in each plot and, in wheat only, collected with a vacuum sampler. All stages of predators seen were collected and reared in the laboratory to estimate mortality and parasitism rates. Overwintering survival outdoors of Coccinella septempunctata L. was studied in partly sheltered and exposed netting cages over dense ground cover. At least 90% of predator eggs hatched in the laboratory, and no parasites were reared from them or from larvae. In cereals, there were significantly fewer larvae than eggs of Coccinellidae, probably because of cannibalism, whereas eggs and larvae of Chrysoperla carnea and Syrphidae (mainly Episyrphus balteatus Deg.) occurred in similar numbers. Unlike Coccinellidae, however, there were fewer cocoons of C. carnea and syrphid pupae on the shoots than expected. Since larval mortality was apparently small, it is suggested that many larvae pupate in the soil. Two parasite species emerged from coccinellid pupae and one from the adults, compared with two species from C. carnea cocoons and nine species from syrphid pupae. Parasitism rates were usually small (25%). More individuals of Coccinella septempunctata survived overwinter in partly sheltered than in exposed cages.