THE NON-ABUNDANT NUTRIENT (NAN) CONCEPT AS A DETERMINANT OF PREDATOR-PREY FITNESS

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 general ist predators Geocoris punctipes (Say) (Heteroptera: Lygaeidae) and Ch rysoperla carnea Stephens (Neuroptera: Chrysopidae) and the specialist predator of whiteflies Serangium parcesetosum Sicard (Coleoptera: Coc cinellidae) were compared, nutritionally, to determine their relative propensities for predation on Ephestia kuehniella (Zeller) (Lepidopter a: Phycitidae) eggs, silverleaf whitefly nymphs Bemisia argentifolii B ellows and Perring (Homoptera: Aleyrodidae) and Aphis gossypii Clover (Homoptera: Aphididae). Using two prey content parameters, biomass (me asured 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 preda tor's growth requirements to reach the adult stage. From this informat ion and observations regarding developmental periods, prey handling ti mes, extraction efficiencies and conversion efficiencies, we developed a daily time budget for each predator feeding on each of the three ty pes of prey. The number of prey and the time required to satisfy the m ethionine requirement were generally much greater than the numbers and time required for meeting biomass requirements. Of the three species of predators, only S. parcesetosum could survive and reproduce within a reasonable time budget with whiteflies as prey. Cotton aphids also a ppeared to be a marginal prey with respect to methionine content.