Bactrocera dorsalis is one of the most economically important fruit flies around the world. In this study, 454 pyrosequencing was used to identify the bacteria associated with different developmental stages of B. dorsalis. At ≥ 97% nucleotide similarity, total reads could be assigned to 172 Operational Taxonomic Units belonging to six phyla. Proteobacteria dominated in immature stages while Firmicutes dominated in adult stages. The most abundant families were Enterococcaceae and Comamondaceae. The genus Comamonas was most abundant in pupae whereas completely absent in adults. Some identified species had low sequence similarity to reported species indicating the possibility of novel taxa. However, a majority sequence reads were similar to sequences previously identified to be associated with Bactrocera correcta, suggesting a characteristic microbial fauna for this insect genus. The type and abundance of different bacterial groups varied across the life stages of B. dorsalis. Selection pressure exerted by the host insect as a result of its habitat and diet choices could be the reason for the observed shift in the bacteria groups. These findings increase our understanding of the intricate symbiotic relationships between bacteria and B. dorsalis and provide clues to develop potential biocontrol techniques against this fruit fly.

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Since 2004 the oriental fruit fly, Bactrocera dorsalis (Hendel) has become widespread and economically important in Wuhan, Hubei Province, central China. In this article, the population dynamics of B. dorsalis were monitored using methyl eugenol-baited traps during 2008-2009 in Wuhan. Adults were captured from early July to the end of December in a citrus orchard and peaked in October and early November. Adult population peak coincided with the ripeness period of sweet oranges in October. Infestation with B. dorsalis was more serious in 2009 than in 2008. Field surveys of host plants for this fly species combined with rearing experiments indicated that pear was the first host plant infested by B. dorsalis. We recorded the following host shift pattern: pear (Pyrus communis L.), jujube (Zizyphus jujuba L.), persimmon (Diospyros kaki L.), and sweet orange (Citrus unshiu Marcor). Our findings suggest that B. dorsalis completes four to five generations per year in this area and most serious damage occurred in the 4th generation in the citrus orchards. The availability of preferred host fruits and the low winter temperature are key factors influencing population fluctuations. Overwintering potential experiments of adults, larvae, and pupae were also carried out in the field. Results suggest that a small proportion of pupae were able to survive winter in Wuhan and emerged successfully the following year. Practical and theoretical implications of the results regarding the invasion potential and management strategy of B. dorsalis in Hubei Province are discussed.

Bactrocera minax is a major citrus pest distributed in China, Bhutan and India. The long pupal diapause duration of this fly is a major bottleneck for artificial rearing and underlying mechanisms remain unknown. Genetic information on B. minax transcriptome and gene expression profiles are needed to understand its pupal diapause. High-throughput RNA-seq technology was used to characterize the B. minax transcriptome and to identify differentially expressed genes during pupal diapause development. A total number of 52,519,948 reads were generated and assembled into 47,217 unigenes. 26,843 unigenes matched to proteins in the NCBI database using the BLAST search. Four digital gene expression (DGE) libraries were constructed for pupae at early diapause, late diapause, post-diapause and diapause terminated developmental status. 4,355 unigenes showing the differences expressed across four libraries revealed major shifts in cellular functions of cell proliferation, protein processing and export, metabolism and stress response in pupal diapause. When diapause was terminated by 20-hydroxyecdysone (20E), many genes involved in ribosome and metabolism were differentially expressed which may mediate diapause transition. The gene sets involved in protein and energy metabolisms varied throughout early-, late- and post-diapause. A total of 15 genes were selected to verify the DGE results through quantitative real-time PCR (qRT-PCR); qRT-PCR expression levels strongly correlated with the DGE data. The results provided the extensive sequence resources available for B. minax and increased our knowledge on its pupal diapause development and they shed new light on the possible mechanisms involved in pupal diapause in this species.

The Chinese citrus fly, Bactrocera minax, is a major tephritid fruit fly pest that infests Citrus spp. fruits. The pest was removed from the national quarantine pest list in China in 2009 owing to its wide spread across the country, and it is currently considered a major threat to citrus industry in Asia. The frequent high infestation levels of B. minax in China emphasize the need for a more comprehensive understanding of its biology and ecology so that more efficient control measures can be developed and applied. In the framework of developing a sterile insect technique program against B. minax, we studied the feeding and mating activities of B. minax in situ (Citrus orchards and surrounding habitats) through open field surveys and video recordings. In the pre-oviposition period, sexually immature adults largely foraged for food (e.g. honeydew from aphids, nectar and sooty mould) on non-host plants. Then, sexually mature adult flies shifted to lick sooty moulds, bird faeces and, to a lesser extent, an unknown substance on the Citrus leaves and fruits during the mating and oviposition periods. Finally, during the post-oviposition period, the flies were observed feeding on ooze from grapes. The mating behaviour patterns of B. minax in the field were described as follows: first, the male established its territory close to the potential oviposition substrate (Citrus fruit), second, the female landed on the fruit and began inspection and ovipositor boring behaviour on the fruit surface (no male courtship observed e.g. wing vibration), and third, the male mounted and copulated with the female. The present study shed light on the feeding ecology and mating behaviour of B. minax in the field; this knowledge will facilitate development of better management strategies against this tephritid fly.

RNA interference (RNAi) has considerable promise for developing novel pest control techniques, especially because of the threat of the development of resistance against current strategies. For this purpose, the key is to select pest control genes with the greatest potential for developing effective pest control treatments. The present study demonstrated that the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase; HMGR) gene is a potential target for insect control using RNAi. HMGR is a key enzyme in the mevalonate pathway in insects. A complete cDNA encoding full length HMGR (encoding an 837-aa protein) was cloned from Helicoverpa armigera (Lepidoptera: Noctuidae). The HaHMGR (H. armigera HMGR) knockdown using systemic RNAi in vivo inhibited the fecundity of the females, effectively inhibited ovipostion, and significantly reduced vitellogenin (Vg) mRNA levels. Moreover, the oviposition rate of the female moths was reduced by 98% by silencing HaHMGR compared to the control groups. One-pair experiments showed that both the proportions of valid mating and fecundity were zero. Furthermore, the HaHMGR-silenced females failed to lay eggs (approximate 99% decrease in oviposition) in the semi-field cage performance. The present study demonstrated the potential implications for developing novel pest management strategies using HaHMGR RNAi in the control of H. armigera and other insect pests.

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