The functions of plant feeding in the omnivorous predator Dicyphus hesperus: water places limits on predation

1. Dicyphus hesperus Knight (Heteroptera: Miridae) nymphs were fed from egg hatch to the adult stage on Ephestia kuehniella eggs provided either alone or in combination with tomato leaves or with a supplementary water source. 2. Only 6% of individuals completed nymphal development on a diet of eggs a lone. In contrast, a high proportion of nymphs completed development on a d iet of eggs when either tomato leaves (97%) or a supplementary water source (88%) were provided. 3. The development times of nymphs given access to leaves were significantl y shorter than those of nymphs given access only to supplementary water. 4. Adult female D. hesperus that were given access to tomato leaves prior t o feeding trials consumed significantly more eggs in a 4-h period than fema les that were dehydrated before trials. Dehydrated females that were allowe d access to water for 3 h before trials consumed an intermediate number of eggs. 5. Plant feeding or access to some other water source is required for prey feeding, growth, and development in D. hesperus, and acquisition of water i s proposed as a primary function of plant feeding. In addition, D. hesperus derives nutrients from plant feeding that increase the rate of nymphal dev elopment, although nymphs cannot complete development when provided only wi th tomato leaves. 6. Three simple models are presented of feeding behaviour in predatory Hete roptera where the amount of plant feeding either decreases, increases, or i s constant as a function of the amount of prey feeding. The models are disc ussed with reference to the results and the probable multifunctional nature of plant feeding in predatory Heteroptera.