Sterile Insect Technique and Control of Tephritid Fruit Flies: Do Species With Complex Courtship Require Higher Overflooding Ratios?

The sterile insect technique (SIT) is widely used to suppress or eradicate tephritid fruit fly pests that threaten agricultural crops. The SIT entails the production, sterilization, and release of large numbers of the target pest species, with the goal of achieving sterile male by wild female matings, which result in infertile eggs and the subsequent reduction of the wild pest population. The success of this control strategy depends, to a large extent, on the ability of released, sterile males to compete successfully against wild males to achieve copulations with wild females. Lance and McInnis (2005) proposed that species with greater male involvement in courtship and mating are less amenable to the SIT than species with simple courtship, because strong artificial selection characteristic of mass-rearing environments is more likely to generate greater behavioral modification to complex than simple courtship and thus to result in increased rejection by wild females. Consistent with Lance and McInnis (2005), the mating competitiveness of mass-reared males of the Mediterranean fruit fly, <it>Ceratitis capitata</it> (Wiedemann), a species with complex male courtship, is substantially lower than that of mass-reared males of the melon fly, <it>Bactrocera cucurbitae</it> (Coquillett), or the oriental fruit fly, <it>Bactrocera dorsalis</it> (Hendel), two species with very simple male courtship. In light of this difference in mating ability, we tested the prediction that higher overflooding ratios (sterile:wild males; OFR) would be required to control populations of <it>C</it>. <it>capitata</it> than of the <it>Bactrocera</it> spp. Levels of induced egg sterility achieved under different OFRs were compared to the “net sterility target,” computed as the proportional decrease in a species’ intrinsic birth rate (realized via SIT) required to balance the intrinsic rate of death and found to be ∼80% for the three species considered. Although the data are scant, they generally support the prediction. For <it>B</it>. <it>cucurbitae</it>, OFRs < 50:1 resulted in egg sterility levels near 80%, whereas in <it>C</it>. <it>capitata</it> similarly high sterility values were achieved only with OFRs >300:1. Likewise, relative to populations in control (untreated) sites, populations in release areas were reduced >99% at OFRs of 50:1–100:1 for <it>B</it>. <it>cucurbitae</it> in Japan compared to reductions for <it>C</it>. <it>capitata</it> of 50–93% at OFRs between 700:1–3,160:1 in Nicaragua and about 80% for OFRs between 100:1–400:1 in Hawaii. The implications of these findings for fruit fly SIT are discussed.