Additional Tests on the Efficacy of Ginger Root Oil in Enhancing the Mating Competitiveness of Sterile Males of the Mediterranean Fruit Fly, Ceratitis capitata (Diptera: Tephritidae)

Recent studies have shown that exposure to the aroma of ginger root oil (Zingiber officinale Roscoe; termed GRO hereafter) increases the mating competitiveness of males of the Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann). This result suggests that pre-release exposure of sterile males to GRO might increase the effectiveness of the Sterile Insect Technique (SIT) against this important agricultural pest. Here, we present the results of two experiments that further investigate the utility of GRO in medfly SIT. In the first, we compare the effectiveness of GRO obtained from three different suppliers in enhancing the mating success of sterile males relative to wild-like males in competition for wild-like females. Following adult exposure to GRO in large, holding boxes, we found significant variation in the mating success of sterile males exposed to GRO from different sources. However, regardless of the source, GRO-exposed males obtained significantly more matings than control, non-exposed males. In the second experiment, we found that the introduction of GRO (using two different doses) to closed, paper buckets at the time of pupal placement resulted in increased mating success of subsequently emerged sterile males. The use of GRO in SIT programs is discussed in light of these findings. Introduction Recent studies (Shelly et al. 2004a and references therein) have shown that exposure to ginger root oil (Zingiber officinale Roscoe; termed GRO hereafter) increases the mating competitiveness of males of the Mediterranean fruit fly (or medfly), Ceratitis capitata (Wiedemann). These studies have generated several observations suggesting that pre-release, adult exposure to GRO, which contains a powerful male attractant (the hydrocarbon sesquiterpene, α-copaene; Flath et al. 1994), may be useful in improving the effectiveness of the Sterile Insect Technique (SIT) against this pest: 1) Males need not feed on GRO to gain a mating advantage; exposure to the aroma alone is effective (Shelly 2001); 2) GRO is effective at low doses. For example, application of as little as 0.125 ml of GRO to the screen-covered top of a large eclosion box (a so-called PARC box, holding ≈ 36,000 males in 0.1 m volume) increased mating success approximately 50% above that observed for control males deprived of GRO (Shelly et al. 2004a); 3) Because of the high potency, GRO exposure is a relatively inexpensive procedure. For example, at a dose of 0.5 ml per PARC box, GRO exposure would cost approximately $1.20 per million males or less than 1% of the cost of sterile flies for the California Preventative Release Program ($133 per million; E. Y. Smith, personal communication); 4) GRO exposure confers heightened mating success for as long as 8-10 d after exposure (Shelly 2001); 5) Wild females initially mated to