Abstract
Empirical protocols for assessing the suitability of prey for aphidophagous coccinellids are examined and a modified scheme of categorization is presented. It is argued that prey suitability should be assessed independently for larval development and adult reproduction because of potentially divergent nutritional requirements between these life stages. A scheme is proposed for assessing prey suitability for larval development using conspecific eggs as a reference diet against which diets of various prey types can be compared both within and among coccinellid species. Among suitable prey (those that support ca. 100% survival of larvae to the adult stage), those that promote faster development and yield larger adults relative to a conspecific egg diet are considered "optimal" for larvae. Prey that yield viable adults with similar or reduced adult weight after a similar or extended period of development relative to a diet of conspecific eggs are classified as "adequate". Prey are "marginal" if they support the survival of some larvae, but significantly less than 100%. Supplementary water should be provided with any non-aphid diet (e.g. pollen and alternative sources of animal protein) given the potential for food-specific diet-drought stress interactions. For adults, suitable prey are classified as "adequate" if they support the production of viable eggs when fed as a monotypic diet, or "marginal" if they merely prolong adult life relative to a water source. Prey that comprise an optimal or adequate diet for both larval development and adult reproduction are termed "complete" and these can be indexed for relative suitability according to derived estimates of rm. Potential sources of error in diet evaluation studies are identified and discussed.
Highlights
Effective and standardized approaches to evaluating the various life-history consequences of prey consumption are essential to laboratory assessments of the biological control potential of predatory insects
Relative prey suitability for development and reproduction is a primary determinant of the numerical response of predator populations, just as host suitability is for parasitoid populations
Since consumption of just one conspecific egg by a neonate larva can favorably influence subsequent larval performance (Osawa, 2002), neonate egg cannibalism likely represents an unrecognized source of variation in life history parameters in many larval feeding experiments and should be carefully controlled in all experiments that seek to assess prey suitability for larval development
Summary
Effective and standardized approaches to evaluating the various life-history consequences of prey consumption are essential to laboratory assessments of the biological control potential of predatory insects. Relative prey suitability for development and reproduction is a primary determinant of the numerical response of predator populations, just as host suitability is for parasitoid populations. Determination of prey suitability for insects that are aphid predators only in their larval stages (e.g. Chrysopidae, Hemerobiidae, and Syrphidae) is relatively straightforward: prey that support completed development are suitable – the faster the development and/or the larger the adult, the more suitable the prey. Evaluation of prey suitability becomes more complex for insects that are predatory in both immature and adult stages since both developmental and reproductive criteria must be examined. Such is the case for aphidophagous coccinellids
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