Andrew Jessup

Mating Compatibility Among Four Pest Members of the Bactrocera dorsalis Fruit Fly Species Complex (Diptera: Tephritidae)

ABSTRACT Bactrocera dorsalis (Hendel), Bactrocera papayae Drew & Hancock, Bactrocera philippinensis Drew & Hancock, and Bactrocera carambolae Drew & Hancock are pest members within the B. dorsalis species complex of tropical fruit flies. The species status of these taxa is unclear and this confounds quarantine, pest management, and general research. Mating studies carried out under uniform experimental conditions are required as part of resolving their species limits. These four taxa were collected from the wild and established as laboratory cultures for which we subsequently determined levels of prezygotic compatibility, assessed by field cage mating trials for all pair-wise combinations. We demonstrate random mating among all pair-wise combinations involving B. dorsalis, B. papayae, and B. philippinensis. B. carambolae was relatively incompatible with each of these species as evidenced by nonrandom mating for all crosses. Reasons for incompatibility involving B. carambolae remain unclear; however, we observed differences in the location of couples in the field cage for some comparisons. Alongside other factors such as pheromone composition or other courtship signals, this may lead to reduced interspecific mating compatibility with B. carambolae. These data add to evidence that B. dorsalis, B. papayae, and B. philippinensis represent the same biological species, while B. carambolae remains sufficiently different to maintain its current taxonomic identity. This poses significant implications for this groups systematics, impacting on pest management, and international trade.

Comparison of in Vitro Heat and Cold Tolerances of the New Invasive Species Bactrocera invadens (Diptera: Tephritidae) with Three Known Tephritids

ABSTRACT Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae) is spreading throughout central Africa attacking a variety of fruit; quarantines are placed on fruit from this region that are considered hosts. The only phytosanitary treatment that is commercially available is an ionizing irradiation treatment for all Tephritidae at 150 Gy. The development of other treatments, such as heat, cold, or fumigation, usually requires testing tens of thousands of insects at a dose that provides efficacy and may take several years. It may be possible to shorten the time required to develop treatments by comparing tolerance of a new quarantine pest to tolerances of pests with similar behaviors and modes of infestation for which treatment schedules are available. Cold and heat tolerance of B. invadens was compared with tolerance of Anastrepha ludens (Loew), Bactrocera dorsalis (Hendel), and Ceratitis capitata (Wiedemann) in vitro. Third-instar B. invadens was no more cold tolerant than the other species when treated in diet at 0.94 ± 0.65°C and no more heat tolerant than C. capitata when immersed in vials in water at 44.7 ± 0.1°C. The data at 0.94 ± 0.65°C was used to include B. invadens in a USDA cold treatment schedule for citrus fruit from Africa so that trade would not be interrupted while protecting U.S. agriculture from this invasive pest.

Development of Phytosanitary Cold Treatments for Oranges Infested with Bactrocera invadens and Bactrocera zonata (Diptera: Tephritidae) by Comparison With Existing Cold Treatment Schedules for Ceratitis capitata (Diptera: Tephritidae)

ABSTRACT Phytosanitary cold treatments were tested for Bactrocera invadens Drew, Tsuruta, and White and Bactrocera zonata (Saunders) using comparisons with Ceratitis capitata (Wiedemann). Oranges were infested by puncturing holes in the peel and allowing tephritids to oviposit in the holes. The treatments were initiated when the larvae reached late third instar because previous research had shown that stage to be the most cold tolerant for all three species. Results show that B. invadens is not more cold tolerant than C. capitata and B. zonata at 1.0±0.1°C and lend support to the use of C. capitata cold treatment schedules for B. invadens. It cannot be concluded that B. zonata is not more cold tolerant than C. capitata.

Mating compatibility among Bactrocera cucurbitae (Diptera: Tephritidae) populations from three different origins

Distinct host ranges of the melon fly, Bactrocera cucurbitae (Coquillett), have been reported among different island populations, suggesting significant genetic divergence. Thus, for the application of the sterile insect technique (SIT), it is important to ensure that released flies are sexually fully compatible with each other and with the laboratory strains. Mating tests among the following strains of the melon fly, B. cucurbitae: Mauritius laboratory‐adapted (35 generations), Seychelles laboratory‐adapted (24 generations), and Hawaii genetic sexing strain (90 generations), were conducted in field cages at the FAO/IAEA Agriculture and Biotechnology Laboratories in Seibersdorf, Austria during the months of August/September 2009. The genetic sexing strain, developed in Hawaii in 2001, allows separation of females and males on the basis of pupal colour. Two separate series of trials were run simultaneously. In the first, melon fly females from Mauritius were the target strain and the competing males were from Mauritius, Seychelles, and Hawaii (GSS). In the second trial, melon fly females from the Seychelles selected among competing males from the same three populations. Sexual activity was similar among the melon fly populations and no significant non‐random, assortative mating was observed. Therefore, it is suggested that melon flies from Mauritius, Seychelles and the Hawaii are compatible, at least under semi‐natural conditions.

Effects of laboratory colonization on Bactrocera dorsalis (Diptera, Tephritidae) mating behaviour: 'what a difference a year makes'.

Abstract Laboratory-reared insects are widely known to have significantly reduced genetic diversity in comparison to wild populations; however, subtle behavioural changes between laboratory-adapted and wild or ‘wildish’ (i.e., within one or very few generations of field collected material) populations are less well understood. Quantifying alterations in behaviour, particularly sexual, in laboratory-adapted insects is important for mass-reared insects for use in pest management strategies, especially those that have a sterile insect technique component. We report subtle changes in sexual behaviour between ‘wildish’ Bactrocera dorsalis flies (F1 and F2) from central and southern Thailand and the same colonies 12 months later when at six generations from wild. Mating compatibility tests were undertaken under standardised semi-natural conditions, with number of homo/heterotypic couples and mating location in field cages analysed via compatibility indices. Central and southern populations of Bactrocera dorsalis displayed positive assortative mating in the 2010 trials but mated randomly in the 2011 trials. ‘Wildish’ southern Thailand males mated significantly earlier than central Thailand males in 2010; this difference was considerably reduced in 2011, yet homotypic couples from southern Thailand still formed significantly earlier than all other couple combinations. There was no significant difference in couple location in 2010; however, couple location significantly differed among pair types in 2011 with those involving southern Thailand females occurring significantly more often on the tree relative to those with central Thailand females. Relative participation also changed with time, with more southern Thailand females forming couples relative to central Thailand females in 2010; this difference was considerably decreased by 2011. These results reveal how subtle changes in sexual behaviour, as driven by laboratory rearing conditions, may significantly influence mating behaviour between laboratory-adapted and recently colonised tephritid fruit flies over a relatively short period of time.

Interchromosomal duplications on the Bactrocera oleae Y chromosome imply a distinct evolutionary origin of the sex chromosomes compared to Drosophila.

Background Diptera have an extraordinary variety of sex determination mechanisms, and Drosophila melanogaster is the paradigm for this group. However, the Drosophila sex determination pathway is only partially conserved and the family Tephritidae affords an interesting example. The tephritid Y chromosome is postulated to be necessary to determine male development. Characterization of Y sequences, apart from elucidating the nature of the male determining factor, is also important to understand the evolutionary history of sex chromosomes within the Tephritidae. We studied the Y sequences from the olive fly, Bactrocera oleae. Its Y chromosome is minute and highly heterochromatic, and displays high heteromorphism with the X chromosome. Methodology/Principal Findings A combined Representational Difference Analysis (RDA) and fluorescence in-situ hybridization (FISH) approach was used to investigate the Y chromosome to derive information on its sequence content. The Y chromosome is strewn with repetitive DNA sequences, the majority of which are also interdispersed in the pericentromeric regions of the autosomes. The Y chromosome appears to have accumulated small and large repetitive interchromosomal duplications. The large interchromosomal duplications harbour an importin-4-like gene fragment. Apart from these importin-4-like sequences, the other Y repetitive sequences are not shared with the X chromosome, suggesting molecular differentiation of these two chromosomes. Moreover, as the identified Y sequences were not detected on the Y chromosomes of closely related tephritids, we can infer divergence in the repetitive nature of their sequence contents. Conclusions/Significance The identification of Y-linked sequences may tell us much about the repetitive nature, the origin and the evolution of Y chromosomes. We hypothesize how these repetitive sequences accumulated and were maintained on the Y chromosome during its evolutionary history. Our data reinforce the idea that the sex chromosomes of the Tephritidae may have distinct evolutionary origins with respect to those of the Drosophilidae and other Dipteran families.

Effect of the symbiont Candidatus Erwinia dacicola on mating success of the olive fly Bactrocera oleae (Diptera: Tephritidae)

Mutualistic bacterial endosymbionts provide many benefits to their insect hosts, but their role in mating has not been studied in the past. In this study, we examined copulatory success and mating latency as two parameters of mating success to assess the influence of Candidatus Erwinia dacicola on mating between a laboratory population of olive flies (Bactrocera oleae Rossi) of Israel origin and a wild population of olive flies from Israel. Previous studies have shown that in many species of tephritid flies, laboratory-reared males have lower fitness and achieve fewer matings than wild males. Our research has shown that this Israeli population of olive flies reared in the laboratory on an artificial diet lacked an endosymbiont, Ca. E. dacicola, found in wild-caught insects from Israel. We hypothesized that decreased fitness and mating ability in laboratory-reared flies could be due to the absence of this endosymbiont. Mating assays between both sexes of these two Israeli populations revealed matings to occur primarily between laboratory-reared females and wild males. Laboratory-reared males achieved only 22% of the total matings. Candidatus Erwinia dacicola was found in significantly fewer insects from the laboratory population than in the wild population; within populations, male and female olive flies were equally likely to have the endosymbiont. However, differences in readiness to mate between the two populations, and not the presence of the endosymbiont, explained mating latency.