Preimaginal survival and development of Coleomegilla maculata and Hippodamia convergens (Coleoptera : Coccinellidae) reared on Acyrthosiphon pisum: Effects of host plants

Coleomegilla maculata (DeGeer) and Hippodamia convergens Guerin-Meneville l arvae were supplied daily with approximate to1.2,2.2,4.3,8.2, or 16.4 mg of Acyrthosiphon pisum Harris retired on either alfalfa Medicago sativa L. (' OK08') or faba beans Vicia faba L. ('Windsor'). Myristic acid and total fat ty acid content (mug/mg aphid fresh weight) were 6.3 and 2.7 times greater, respectively, in pea. aphids reared on alfalfa as compared with faba beans , resulting in a 1.17-fold increase in caloric content. Higher survival rat ios were observed for both C. maculata and H. convergens supplied with low daily prey levels of pea aphids reared on alfalfa versus faba beans, but no differences were observed at higher prey levels. When pea aphids reared on alfalfa were supplied to C. maculata and H. convergens larvae at low prey levels, preimaginal developmental times were significantly reduced compared with those supplied with pea aphids reared on faba beans at the same prey levels. At higher daily pea aphid levels, G. maculata and H. convergens dev elopmental times were not significantly different between host plants. At l ower daily prey levels, C maculata and H. convergens elliptic at body g er area was larger when supplied with pea aphids reared on alfalfa, but body a reas were similar at hi h daily prey levels. Convergence of survival ratios , developmental times, and elliptical body areas for C. maculata and H. con vergens! at high (less limiting) prey levels supports the hypothesis that d ifferences in prey nutritional value between pea aphids reared on alfalfa v ersus faba beans are quantitative and appear to be primarily influenced by differences in pea aphid myristic acid content.