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

Simple Summary Tephritid fruit flies are highly invasive, globally important insect pests of horticulture. Significant effort goes into assessing and managing the risks posed by fruit flies, while substantial investments are made into their control. An important factor in the biology of fruit flies is competition. Different species of fruit fly compete over access to fruit, with more-competitive species able to displace less-competitive species in time, space and host usage. While this behaviour is very well documented scientifically, it is rarely incorporated into pest risk assessment or pest management investment. Targeting regulators and decision makers, this paper reviews the science underpinning our knowledge of fruit fly competition, and then identifies four major effects of fruit fly competition that could impact pest risk planning or large-scale pest management initiative. These are: (i) numerical reduction of an existing fruit fly pest following competition with 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. 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.