Time-Specific Life Tables for Acyrthosiphon kondoi (Homoptera: Aphididae) in First Crop Alfalfa in Oklahoma

Abstract

Time-specific life tables were developed for Acyrthosiphon kondoi Shinji in Oklahoma during growth of the first alfalfa crop in 1985 and 1986. In each year, population densities increased rapidly (from 200 aphids per stem) during a 2–3-wk period between early March and May. In the first interval of population growth each year, the observed rates were equivalent to the intrinsic rate of increase determined in laboratory studies. Although alatae were produced throughout the period of population growth, a rapid increase in the prevalence of this morph resulted in proportions of winged adults exceeding 90% just before population decline. A rapid decrease in numbers of A. kondoi from the peak densities occurred due to emigration of alatae and the resulting decrease in nymphal production. Although predaceous insects (primarily Hippodamia convergens Guerin-Meneville) were present in moderate numbers (up to 0.2 individuals per stem), there was little evidence of limitation imposed on the growth rates of the aphid population. We observed no parasitized or diseased aphids and it appeared that natural controls were not effective in slowing the rapid growth of populations and preventing outbreaks during our study. Except for emigration of alatae, no factors were identified that reduced population densities by detectable amounts.