Modifications to torula yeast borax-baited traps and their impact on the attraction of tephritid fruit flies (Diptera: Tephritidae)

Traps containing food-based attractants are an important component of regional networks operated to detect invasive tephritid fruit flies (Diptera: Tephritidae), which pose a serious threat to fruit and vegetable production worldwide. However, food baits are weak attractants, and there is a critical need to increase their effectiveness. A recent study demonstrated that the addition of ammonium acetate crystals to an aqueous torula yeast borax (TYB, a commonly used food bait) solution significantly increased captures of Mediterranean fruit flies, Ceratitis capitata (Wiedemann), and oriental fruit flies, Bactrocera dorsalis (Hendel), but not melon flies, Zeugodacus cucurbitae (Coquillett). The present study investigated 2 alternative methods for providing ammonium acetate in TYB-baited traps. First, a cylinder containing ammonium acetate was affixed to the inner, upper surface of traps above the standard TYB solution, and this resulted in significantly higher captures of C. capitata, but not B. dorsalis or Z. cucurbitae, than observed for traps baited with standard TYB. Second, ammonium acetate was incorporated directly into field-ready TYB pellets. However, these had no effect on C. capitata and even appeared to repel Z. cucurbitae. Two additional modifications were investigated: (i) extra amounts of certain amino acids or (ii) ground brine shrimp were added to TYB. The increased levels of amino acids significantly enhanced captures of C. capitata but not B. dorsalis or Z. cucurbitae. Addition of shrimp powder did not positively influence trap catch for any species. Implications of these results for detection trapping are discussed.