Using molecular gut content analysis to identify key predators in a classical weed biological control system: a study with Neomusotima conspurcatalis (Lepidoptera: Crambidae)

Predators can severely limit or prevent the establishment of newly introduced biological control agents. Identifying key predators and quantifying their impacts, however, has often proved difficult, especially in cases where the biological control agent has low establishment or detectability. We used molecular gut content analysis to identify predators feeding on Neomusotima conspurcatalis Warren (Lepidoptera: Crambidae), a biological control agent for Lygodium microphyllum (Cavanilles) R Brown (Lygodiaceae), an invasive weed in Florida, USA. We developed DNA primers specific to N. conspurcatalis, and conducted laboratory feeding trials to confirm that agent DNA could be detected in predator guts through PCR amplification. We then released N. conspurcatalis at three L. microphyllum infested sites and one week later conducted field surveys for predators. Our experimental field survey indicated that predatory arthropods were attracted to the immediate locations of N. conspurcatalis releases. A total of 351 predatory arthropods were collected from L. microphyllum infested sites, representing a broad taxonomic range. At least 33% of individuals from all 13 taxa analyzed had fed on N. conspurcatalis. Of the four predator functional groups encountered, spiders were the most numerous, and appeared to be the most important group based on predation rate. Our results can inform the N. conspurcatalis release program, providing guidance on avoiding generating predation hotspots, and facilitating predictions about where and when N. conspurcatalis releases are most likely to result in establishment. Additionally, we highlight the potential of molecular gut content analysis to improve our understanding of the effects of predators on newly introduced classical biological control agents.