The potential of the hoverfly Allograpta exotica as a biological control agent of the strawberry aphid Chaetosiphon fragaefolii

Abstract

Syrphid larvae are effective biological control agents in numerous crops due to their voracity, and they are used in both augmentative and conservation-based strategies within horticultural systems. This study conducted laboratory trials to ascertain the predation rate of Allograpta exotica (Wiedemann) (Diptera: Syrphidae) on Chaetosiphon fragaefolii (Cockerell) (Hemiptera: Aphididae) and to compare it with the predation rate on Aphis gossypii Glover (Hemiptera: Aphididae), another significant aphid species affecting strawberries. Additionally, field trials were conducted to assess the reduction in the field population of C. fragaefolii achieved by A. exotica within strawberry crops. We observed a significant increase in the number of aphids consumed by a larva as it progressed from first-instar larvae (L1) to third-instar larvae (L3). Specifically, the mean aphid consumption by second-instar larvae (L2) was nearly 11 times higher for C. fragaefolii and 10 times higher for A. gossypii compared to L1. Furthermore, the consumption rate of L3 larvae was approximately 2 times higher for both aphid species compared to L2. In laboratory conditions, A. exotica larvae significantly reduced the number of both aphid species, but the control on A. gossypii was higher than on C. fragaefolii. The results of the field experiment demonstrated that the predatory hoverfly A. exotica significantly reduced the numbers of C. fragaefolii compared to the control treatment, highlighting its potential as a promising biological control agent in strawberry crops.