Description and quantification of field attack rates by predatory mites: An example using an electrophoresis method with a species of Antarctic mite.

Polyacrylamide gel electrophoresis and subsequent esterase staining provide an alternative to immunological methods for investigating the diet of microarthropods which cannot be observed directly. Attack rates in field populations of Antarctic microarthropods by the predator Gamasellus racovitzai were calculated by proportional and quantitative analyses of electrophoresis results. Results were quantified by transmission densitometry and a digestion curve for ingested prey esterases was defined. An exponential decay model of digestion, incorporating meal size, was used, and a method potentially enabling both the time since feeding and the composite meal size to be estimated for individual predators is described. These methods are applied to samples of predatory mites collected from the Antarctic Peninsula. Although estimated attack rates were low, about 0.1-0.3 prey per predator per day, they may be sufficient to cause severe local reduction in prey density.

Laboratory studies of predation by the Antarctic mite Gamasellus racovitzai (Acarina: Mesostigmata).

Laboratory investigations of predation by Gamasellus racovitzai (Acarina: Mesostigmata) on Cryptopygus antarcticus (Insecta: Collembola) are described. The predator appeared to search at random, but, when contact with prey had been made, a rapid attack involved looping the forelegs over the prey to hold it whilst the chelicerae moved forward horizontally to puncture the side of the prey. The mean predation rate by deutonymphs, approximately one prey per predator per 12 days, was independent of prey density, but with adults this rate increased to about one prey per predator per 3 days. A study of leg geometry predicted a maximum prey size that could be captured: some experimental evidence suggested that mites selected prey near to this predicted size. The contribution of the laboratory results towards understanding the dynamics of field populations is discussed.

Studies on populations of Folsomia candida (Insecta: Collembola) : The productivity of populations in relation to food and exploitation.

Experiments are described that were designed to investigate the effects of food availability and rate of exploitation on the growth and production of populations of Folsomia candida (Willem). In an initial experiment in which there was excess food it was found that increasing the rate of exploitation resulted in increases in both the numerical and biomass productivity of the populations. In a second experiment it was shown that, when there is severe competition for food, the rate of exploitation does not affect either the biomass or the numerical production. It is concluded that the effect of overcrowding, in the form of competition for space, does contribute to the growth in numbers of populations, but that the supply of food plays a more important role in regulating the population. Anomalous results, showing that exploitation has a lesser effect when there is severe competition for food, are discussed.