Foraging behaviour of Scymnus syriacus (Coleoptera: Coccinellidae) provided with Aphis spiraecola and Aphis gossypii (Hemiptera: Aphididae) as prey: Functional response and prey preference

Abstract

Scymnus syriacus Marseul is one of the most important biocontrol agents of aphids in citrus orchards. Understanding the effi ciency and host specifi city of natural enemies can help improve their effectiveness as biological control agents of particular pests. In this study, the functional response, preference and switching behaviour of different stages of S. syriacus feeding on Aphis spiraecola Patch and Aphis gossypii Glover, on orange leaves, were studied under laboratory conditions of 27 ± 2°C, 65 ± 5% RH and a photoperiod of 16L: 8D. The results indicate that 4th instar larvae and adult males and females of this predator exhibit a type II functional response when offered different numbers (3, 5, 7, 10, 20, 30, 40, 60 and 80) of both A. spiraecola and A. gossypii. Adult females had signifi cantly higher attack rates (a) on both species of aphids. Handling times (Th) of adult male predators on A. spiraecola and those of 4th instar larvae on A. gossypii were shorter than that of the other stages. In no-choice preference experiments, adult females fed equally on both species of aphid, but the 4th instar larvae preferred A. gossypii. In switching experiments, prey selection was evaluated by simultaneously presenting different ratios (30: 50, 40: 40 and 50: 30) of the two aphids, A. spiraecola: A. gossypii, to the predator. The 4th instar larvae and adult females of S. syriacus showed higher preference for A. gossypii at each ratio offered (except adult females offered the 50: 30 ratio). Based on their foraging behaviour 4th instar larvae and adult females of S. syriacus are suitable for use in integrated management of citrus aphids.