Predator performance: inferring predator switching behaviors based on nutritional indices in a coccinellid–psylla–aphid system

BACKGROUND: Knowledge of the nutritional ecology of predatory coccinellids is important for the selection of efficient biocontrol agents. We examined five species common in pistachio orchards and determined their nutritional indices when fed on the key psylla pest of the system, Agonoscena pistaciae, in contrast to an alternative prey common on herbaceous plants in orchards, Aphis gossypii. RESULTS: Feeding experiments revealed that Oenopia conglobata contaminata and Adalia bipunctata may be more efficient as biocontrol agents for A. pistaciae than for A. gossypii, as A. bipunctata had a high efficiency of conversion of ingested food and a high relative growth rate and O. conglobata contaminata had a high consumption index on psylla prey. In contrast, the nutritional indices of Coccinella undecimpunctata aegyptica, Hippodamia variegata and Exochomus nigripennis suggest that A. gossypii was a more suitable host food. CONCLUSION: Where both the psyllids and the aphids occur in pistachio orchards, especially under conditions of unlimited access to A. gossypii, C. undecimpunctata aegyptica, H. variegata and E. nigripennis may prefer to move from psylla-infested leaves of pistachio trees and travel to and stay on weeds to feed on A. gossypii. The value of using nutritional ecology as a means of understanding and predicting biocontrol outcomes and selecting better candidates for mass rearing is discussed.