Abstract
We applied the non-abundant nutrient concept (NAN), an off-shoot from the ecological concept known as Liebig’s “law of the minimum” or the concept of “limiting factors”, to explain why certain predators are well fitted while others are poorly fitted to their prey. The generalist predatorsGeocoris punctipes (Say) (Heteroptera: Lygaeidae) andChrysoperla carnea Stephens (Neuroptera: Chrysopidae) and the specialist predator of whitefliesSerangium parcesetosum Sicard (Coleoptera: Coccinellidae) were compared, nutritionally, to determine their relative propensities for predation onEphestia kuehniella (Zeller) (Lepidoptera: Phycitidae) eggs, silverleaf whitefly nymphsBemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae) andAphis gossypii Glover (Homoptera: Aphididae). Using two prey content parameters, biomass (measured as dry weight) and methionine (the least abundant protein amino acid in all three prey species), we made estimates of how many of the various kinds of prey would need to be consumed to satisfy each predator’s growth requirements to reach the adult stage. From this information and observations regarding developmental periods, prey handling times, extraction efficiencies and conversion efficiencies, we developed a daily time budget for each predator feeding on each of the three types of prey. The number of prey and the time required to satisfy the methionine requirement were generally much greater than the numbers and time required for meeting biomass requirements. Of the three species of predators, onlyS. parcesetosum could survive and reproduce within a reasonable time budget with whiteflies as prey. Cotton aphids also appeared to be a marginal prey with respect to methionine content.
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