Host Preference, Longevity, Developmental Period and Sex Ratio of Aphelinus asychis1 with Three Sorghum-Fed Species of Aphids2 Held at Controlled Temperatures3

Abstract

Laboratory studies of Aphelinus asychis (Walker), an imported, internal parasite of aphids, conducted at 5 controlled temperatures showed the preference of the parasite for the aphid species in descending order to be: greenbug, Schizaphis graminum (Rondani); corn leaf aphid, Rhopalosiphum maidis (Fitch), and yellow sugarcane aphid, Sipha flava (Forbes). This trend of preference was consistent at all temperatures, combinations of aphids, and when the parasite was caged individually with each aphid species. The longevity of the adult female decreased with increasing temperature, and the 21.1–32°C alternating temperature yielded an approximate midway response. The mean longevity of adults was approximately 18 days at 23.9°C and 9 days at 32.2°C. The highest ratio of females to males occurred at the coolest temperature studied (23.9°C) with approximately 2.4 ♀ to 1 ♂, while at 32.2°C the ratio was about 1:1. The parasites which emerged from all host aphid species were approximately 60% females when averaged over all temperatures. The parasite took approximately 16 days to develop from egg to adult at 23.9°C and 10 days at 32.2°C. The developmental time for the 21.1–32.2°C fluctuating temperatures was 12.5 days. Unmated female A. asychis produced only male progeny.