Sequential invasions by fruit flies (Diptera: Tephritidae) in Pacific and Indian Ocean islands: A systematic review

Comparative adult preference-larval performance relationship between a specialist and a generalist tephritid: Implication for predicting field host-range

Phytophagous insects differ in their degree of specialization to their host plants. It ranges from monophagous or oligophagous species that can only develop on a single host plant, or family of host plants, to extremely polyphagous species that can develop on plants from many distinct botanical families. The aim of this study was to compare the larval performance and adult preference of a highly generalist species, the Queensland fruit fly (Bactrocera tryoni) and a highly specialist species, the breadfruit fruit fly (B. umbrosa) among several fruits covering both species' host range. (i) larval performance was tested on 16 fruit species, and (ii) a female preference was tested on a subset of five fruit species. In addition, (iii) a field survey was carried out on 11 fruit species. B. umbrosa infested only Artocarpus fruits in the field. Accordingly, B. umbrosa larvae survived and developed only on fruits belonging to the Artocarpus genus. Female B. umbrosa did not lay their eggs on non-Artocarpus fruits, except Terminalia catappa. Female B. tryoni, on the other hand, made little selection between the fruits tested, and its larvae developed on 13 of the 16 fruit species tested. The larval performance of both species, adjusted when tested by female preference, predicted in large part the fruit infestation in the field. These data are essential to better estimate invasion risk where the species are not established.

A novel diagnostic gene region for distinguishing between two pest fruit flies: Bactrocera tryoni (Froggatt) and Bactrocera neohumeralis (Hardy) (Diptera: Tephritidae)

Bactrocera tryoni and Bactrocera neohumeralis are morphologically similar sibling pest fruit fly species that possess different biological attributes, geographic distributions, and host ranges. The need to differentiate between the two species is critical for accurate pest status assessment, management, biosecurity, and maintenance of reference colonies. While morphologically similar, adults may be separated based on subtle characters; however, some characters exhibit intraspecific variability, creating overlap between the two species. Additionally, there is currently no single molecular marker or rapid diagnostic assay that can reliably distinguish between B. neohumeralis and B. tryoni; therefore, ambiguous samples remain undiagnosed. Here we report the first molecular marker that can consistently distinguish between B. tryoni and B. neohumeralis. Our diagnostic region consists of two adjacent single nucleotide polymorphisms (SNPs) within the pangolin (pan) gene region. We confirmed the genotypes of each species are consistent across their distributional range, then developed a tetra-primer amplification refractory mutation system (ARMS) PCR assay for rapid diagnosis of the species. The assay utilizes four primers in multiplex, with two outer universal primers, and two internal primers: one designed to target two adjacent SNPs (AA) present in B. tryoni and the other targeting adjacent SNPs present in B. neohumeralis (GG). The assay accurately discriminates between the two species, but their SNP genotypes are shared with other nontarget tephritid fruit fly species. Therefore, this assay is most suited to adult diagnostics where species confirmation is necessary in determining ambiguous surveillance trap catches; maintaining pure colony lines; and in Sterile Insect Technique management responses.

The Global Epidemic of Bactrocera Pests: Mixed-Species Invasions and Risk Assessment

Throughout the past century, the global spread of Bactrocera pests has continued to pose a significant threat to the commercial fruit and vegetable industry, resulting in substantial costs associated with both control measures and quarantine restrictions. The increasing volume of transcontinental trade has contributed to an escalating rate of Bactrocera pest introductions to new regions. To address the worldwide threat posed by this group of pests, we first provide an overview of Bactrocera. We then describe the global epidemic, including border interceptions, species diagnosis, population genetics, geographical expansion, and invasion tracing of Bactrocera pests. We further consider the literature concerning the invasion co-occurrences, life-history flexibility, risk assessment, bridgehead effects, and ongoing implications of invasion recurrences, as well as a case study of Bactrocera invasions of California. Finally, we call for global collaboration to effectively monitor, prevent, and control the ongoing spread of Bactrocera pests and to share experience and knowledge to combat it.

Competition: A Missing Component of Fruit Fly (Diptera: Tephritidae) Risk Assessment and Planning

Tephritid fruit flies are internationally significant pests of horticulture. Because they are also highly invasive and of major quarantine concern, significant effort is placed in developing full or partial pest risk assessments (PRAs) for fruit flies, while large investments can be made for their control. Competition between fruit fly species, driven by the need to access and utilise fruit for larval development, has long been recognised by researchers as a fundamental component of fruit fly biology, but is entirely absent from the fruit fly PRA literature and appears not be considered in major initiative planning. First presenting a summary of the research data which documents fruit fly competition, this paper then identifies four major effects of fruit fly competition that could impact a PRA or large-scale initiative: (i) numerical reduction of an existing fruit fly pest species following competitive displacement by an invasive fruit fly; (ii) displacement of a less competitive fruit fly pest species in space, time or host; (iii) ecological resistance to fruit fly invasion in regions already with competitively dominant fruit fly species; and (iv) lesser-pest fruit fly resurgence following control of a competitively superior species. From these four major topics, six more detailed issues are identified, with each of these illustrated by hypothetical, but realistic biosecurity scenarios from Australia/New Zealand and Europe. The scenarios identify that the effects of fruit fly competition might both positively or negatively affect the predicted impacts of an invasive fruit fly or targeted fruit fly control initiative. Competition as a modifier of fruit fly risk needs to be recognised by policy makers and incorporated into fruit fly PRAs and major investment initiatives.