Using insects as potential vectors of Fusarium tumidum to control gorse

Abstract

The adult light brown apple moth Epiphyas postvittana Walker (Lepidoptera: Tortricidae), gorse seed weevil Apion ulicis Förster, (Coleoptera: Apionidae), gorse pod moth Cydia ulicetana Denis and Schiffermüller (Lepidoptera: Tortricidae) and gorse thrips Sericothrips staphylinus Haliday (Thysanoptera: Thripidae) were assessed for their ability to carry and deposit the conidia of a plant pathogenic fungus Fusarium tumidum Sherb. on agar plates in laboratory experiments. Epiphyas postvittana, the largest insect species studied, carried and deposited the highest number of F. tumidum conidia. The number of colony forming units recovered from all insect species after exposing them to F. tumidum sporulating cultures for 24 h, declined with time. In subsequent transmission experiments using only E. postvittana, each insect was loaded with 5,000 conidia of F. tumidum and caged together with potted healthy gorse (Ulex europaeus L.) at eight insects per plant. The insects deposited 310 conidia per plant on average but neither infection nor plant growth effects resulted. Only directly inoculated plants became infected and were significantly shorter with 42% reduction in fresh shoot weight compared with the control treatment. Epiphyas postvittana on its own did not cause any significant plant damage and did not enhance F. tumidum infection. The insect did not spread the conidia from diseased to healthy plants. The results showed that insects are unlikely to be effective vectors in a ‘lure-load-infect’ approach for biological control of gorse using F. tumidum.