Abstract
The sterile insect technique (SIT) may reduce pest populations by allowing sufficient amount of irradiation-induced sterile males to mate with wild females whilst maintaining mating ability comparable to wild males. Although the SIT methods are well understood, the optimal sterilizing dose and processing development stage for application vary among species. To ensure effective pest control programs, effects of irradiation on physiology, behavior, and gene function in the target species should be defined, however, little is known about irradiation effects in Bactrocera tau. Here, the effects of irradiation on rates of fecundity, egg hatch, eclosion, mating competitiveness, flight capability, morphology of reproductive organs, and yolk protein (YP) gene expression were studied. The results showed that rates of female fecundity and egg hatch decreased significantly (51 ± 19 to 0.06 ± 0.06 and 98.90 ± 1.01 to 0, respectively) when pupae were treated with >150 Gy irradiation. Flight capability and mating competitiveness were not significantly influenced at doses <250 Gy. Ovaries and fallopian tubes became smaller after irradiation, but there was no change in testes size. Finally, we found that expression of the YP gene was up-regulated by irradiation at 30 and 45 days post-emergence, but the mechanisms were unclear. Our study provides information on the determination of the optimal irradiation sterilizing dose in B. tau, and the effects of irradiation on physiology, morphology and gene expression that will facilitate an understanding of sub-lethal impacts of the SIT and expand its use to the control of other species.
Highlights
The Bactrocera (Diptera: tephritidae) comprises one of the major pests of tropical fruits (Jamnongluk et al, 2003), and as a result of its euryphagy on many agricultural crops and rapid range expansion, the pumpkin fruit fly [Bactrocera tau (Walker)] has become a focus of global quarantine and control programs (Yan et al, 2015)
There were no effects of irradiation on fecundity rate when 400 Gy was applied to male flies mated with untreated female flies, fecundity was lower for irradiated females mated with untreated males compared with control
Collins et al suggested that 70–75 Gy could be used as the lowest practical dose rate for B. tryoni (Collins et al, 2008), while 125 Gy irradiation applied to late third instars of B. dorsalis could result in no survival to adult stage (Follett and Armstrong, 2004), and a dose of 85 Gy could be applied to late third instars of B. tau to prevent adult eclosion (Zhan et al, 2015)
Summary
The Bactrocera (Diptera: tephritidae) comprises one of the major pests of tropical fruits (Jamnongluk et al, 2003), and as a result of its euryphagy on many agricultural crops and rapid range expansion, the pumpkin fruit fly [Bactrocera tau (Walker)] has become a focus of global quarantine and control programs (Yan et al, 2015). As a technique with proven high specificity and persistence in controlling other species of Diptera pests, the sterile insect technique (SIT) may be a leading method to reduce populations of B. tau. SITs could reduce pest populations by decreasing the hatch rate of eggs through releasing large amounts of irradiationinduced sterile males, which have a comparable competitive mating ability to wild males, to mate with wild females. The International Consultative Group was the first group to formally recommend genetic treatment of insect pests, and, based on irradiation data for many tephritid fruit fly species and a limited number of other insect pests, the group proposed a dose of gamma irradiation of 150 Gy for fruit flies and 300 Gy for other insects (Follett, 2004). It is important that the mating rates of wild female B. tau with irradiated and control males are not skewed, because reductions in the mating fitness of irradiated males compared with wild males would require larger numbers of insects to be released to avoid failure of a control program (Kean et al, 2011)
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