Study on Biology, Consumption Rate and Seasonal Abundance of Coccinellids (Coccinellidae) under Greenhouse and Field Conditions

Abstract

The biology and seasonal abundance of coccinellids and their'consumption rate on wheat aphids was studied from 1996 to 1999 at Ambo Plant Protection Research center (PPRC). The dominant species of coccinellids were Adonia spp.and Cheilomenes lunata F. The
most widely recorded species of aphids in the experimental site were green bug, Schizaphis graminium (Rondant); the Russian wheat aphid, Diuraphis noxia (Mordvilko); Oat aphids Rhopalosiphutnpadi (L) and English grainaphid, Macrosiphum maidis (Fetch). Under greenhouse trials predator (Ch.lunata F) and aphid (D. noxia) were included. Eggs of Cheilomenes lunata F were laid in bunch, each containing 4-52 egg mass, on leaves close to aphids. The development of eggs lasted 3.0-10 days. The larvae required 12-18 days to develop into pupae. Pupation took up tol2 days under greenhouse conditions. Eggs were orange-yellow and measured 1.0-1.5 mm in diameter. Larvae were 2.0 -10.48 mm long and were brownish grey or light grey to blackish with yellow or white spots depending upon the species. Adult beetles that were brightly colored and 3.0-5.5 mm long could Jive up to 117 days. Both the larvae and adults are aphid predators. It was estimated that a single larva could consume from 11.9-23.8 aphids per day while adults consumed 17.9-52.5 aphids per day. The highest population of aphids recorded was from the end of September upto mid-October whereas coccinellids attained a peak population in mid-October. Both growth stages (larvae and adults) could feed an average of 52.26 aphids per day and they might consume about 2668.31 aphids throughout their life. Studying the biology and seasonal abundance of these predatory insects is essential for better understanding of wheat aphid population dynamics and is useful when developing control programs within the context of IPM.