Effects of Ladybeetle, Harmonia axyridis, Foraging Trails on Behavior of Tamarixia radiata

Abstract

The Asian citrus psyllid, Diaphorina citri, is a threat to citrus production because it transmits the bacterium, Candidatus Liberibacter asiaticus (CLas), which causes huanglongbing (HLB), also known as citrus greening. Insecticide use is the most common tactic for reducing D. citri populations. However, emerging concerns caused by frequent insecticide applications are insecticide resistance and indiscriminate elimination of beneficial organisms. Biological control can potentially contribute to D. citri management but the interactions occurring between natural enemies of this pest are poorly understood. Prominent natural enemies of D. citri in Florida, U.S. include the primary ectoparasitoid, Tamarixia radiata and several species of predacious ladybeetles, often including Harmonia axyridis. We investigated the behavioral response of T. radiata to trail semiochemicals deposited by ladybeetles (H. axyridis) while foraging. The total residence times of T. radiata were shorter on leaves containing H. axryidis trails than on untreated controls. Likewise, both parasitism and host feeding of D. citri nymphs were reduced on whole plants treated with H. axyridis trails as compared with unmarked controls. Wasp behavior was not affected by ladybeetle trail extracts as clearly when similarly treated detached leaves were presented in paired choice tests confined within 9 cm diameter Petri dishes. The results suggest that T. radiata detects predator trails as an indicator of areas where intraguild predators were present, and this information may be used by parasitoids for predator avoidance and decreased competition. The impact of intraguild competition between natural enemies of D. citri on overall biological control deserves further investigation.