The Phenology and Distribution of Aphids in California Alfalfa as Modified by Ladybird Beetle Predation (Coleoptera: Coccinellidae)

Abstract

Can. Ent. 112: 489-495 (1980) The phenologies and distributions of pea aphid (Acyrthosiphon $sum (Harris)), blue alfalfa aphid (A. kondoi (Shinji)), and spotted alfalfa aphid (Therioaphis maculata (Buckton)) were intensively studied in California alfalfa. The results showed, as expected, that aphid populations across all densities were aggregated; but that ladybird beetle (Hippodamia convergens (G.-M.)) predation increased the degree of aggregation. The distribution parameters of the aphids were estimated using methods developed by Iwao and Kuno (1971). The distribution and abundance of prey in the field greatly influence the success of predators and, via nutrition, their survival, growth, and reproduction. A knowledge of these relationships is essential if satisfactory field models of predator-prey interactions are to be developed. This paper is part of a series on the interactions of pea aphid (Acyrthosiphon pisum (Harris)), blue alfalfa aphid (A. kondoi (Shinji)), and spotted alfalfa aphid (Therioaphis maculata (Buckton)) and their ladybird beetle predator Hippodamia convergens (G.-M.) in alfalfa. In this paper we report an analysis of the phenology and distribution of these organisms, and use this information to estimate the influence of prey distribution on predation success of H. convergens in the field. Resume Methods Analysis of Prey Distribution in the FieldLloyd (1967) developed a method ("Patchiness" = x*/Z) which is affected little by changes in density, to measure the distributions of organisms & nature.Patchiness is defined as the ratio of mean crowding (X*) to the mean (X), where X* is defined asand S2 is the population variance. Values of x*/X less than, equal to, or greater than 1 indicate uniform, random, and aggregated distributions respectively. Iwag and Kuno (1971) showed that the slope (P) of the regression line of X* on X provided an equivalent measure of dispersion and, in addition, found that the intercept (a) was a measure of the units of that dispersion (i.e. a + 1).

A CONCEPTUAL MODEL FOR GROWTH, DEVELOPMENT, AND REPRODUCTION IN THE LADYBIRD BEETLE, HIPPODAMIA CONVERGENS (COLEOPTERA: COCCINELLIDAE)

“…convergens are described elsewhere (Gutierrez et al 1980). Figure 9 shows the simulated growth and development of a newly hatched larva in our experimental arena under the conditions of 1, 3, or 5 aphids per stem at a constant temperature of 24.8"C. The results (9A) show that the aging rate (time to reproduction) slows, while growth and fecundity decrease as food supplyldemand decreases.…”

Interspecific variation in the escape responses of aphids: effect on risk of predation from foliar-foraging and ground-foraging predators

“…Both aphid species occur abundantly as early-season and late-season pests of alfalfa in North America (Harper et al 1978;Kodet et al 1982;Flint 1985;Hellman et al 1993;Lamp et al 1994). The aphids feed in aggregations on leaves (growing tips) in the upper canopy of alfalfa where they cause leaf yellowing, stunting, and even plant death (Harper et al 1978;Gutierrez et al 1980;Kodet et al 1982;Hellman et al 1993; J. Losey personal observation). A. pisum feeds on a wide variety of genera in the Fabaceae, whereas A. kondoi appears to be far more specialized, feeding primarily on alfalfa (Medicago sativa) (Harper et al 1978;Kodet et al 1982;Lamp et al 1994).…”

Spatial Variance in Ecology

“…Confusion over assumptions of the method have resulted in inappropriate conclusions when applied to field data (e.g. Byerly et al 1978, Gutierrez et al 1980.…”