Male bait stations containing the fungal pathogen, Beauveria bassiana, kills both male and female fruit flies (Diptera: Tephritidae) through horizontal transfer of spores

The state of Hawaii has five established invasive Tephritidae fruit fly species: Mediterranean fruit fly (Ceratitis capitata), Oriental fruit fly (Bactrocera dorsalis), melon fly (Zeugodacus cucurbitae), Malaysian fruit fly (Bactrocera latifrons) and olive fruit fly (Bactrocera oleae). These and several other tephritid fruit fly species pose serious threats to global food security and economy. An important method of control is the use of attract-and-kill tactics where insecticides are combined with protein baits to target sexually immature adult flies or with male lures to remove large numbers of males (male annihilation technique). Though insecticide laced baits and male lures do not specifically target sexually mature females, in some cases, the insecticide can be horizontally transferred from males to females through food sharing and contact during courtship and mating. Here, we conducted laboratory experiments to determine if horizontal transfer of the entomopathogenic fungus, Beauveria bassiana, would induce mortality in female C. capitata, B. dorsalis, and Z. cucurbitae. We found that males of all three species were susceptible to B. bassiana through forced contact and passive contact in male bait stations. More importantly, for all three species, there was high female mortality when females were caged with B. bassiana-exposed males compared to low or no mortality when females were caged with control males. Thus, horizontal transfer of B. bassiana spores does occur, and suggests that its use could enhance the effectiveness of attract-and-kill bait stations by controlling both sexes.