Prey killing rate of a generalist predator may be enhanced by macronutrient manipulation

Generalist arthropod predators forage not only to gain energy and nutrients, but also to obtain a balanced intake of macronutrients (the intake target). We test two opposite hypotheses concerning the predation rate of nutritionally imbalanced predators: It will increase 1) if the prey is rich in macronutrients that the predator is short of; or 2) if the prey is low in macronutrients that the predator is short of. We used the wolf spider Pardosa amentata (Clerck) as the predator and nutritionally manipulated Drosophila melanogaster Meigen as prey. We completed a full factorial experiment with 8 treatment groups, in which we measured predation, consumption, and prey utilization of high-protein (HP) and high-lipid (HL) flies by spiders that were previously treated with either HP- or HL-flies for 2 or 6 days. The results supported hypothesis 2. Whether spiders had been previously fed HP-or HL-flies, those that were tested against the same type of fly killed more than those tested against the opposite type of fly. A likely explanation for this result is that the predator will be unable to reach its macronutritional intake target by continued feeding on the same prey; it will stay nutritionally imbalanced and continue to catch prey in an attempt to redress its imbalance. In natural systems, predation rates may thus be increased by the widespread mismatch between predators’ nutritional demands and what is available in prey. In practical biological control, this suggests a beneficial effect of feeding the predator prior to release with the pest it is intended to control.

Methods
Predation experiments in the laboratory.