Host reproduction number as an indicator of reproductive advantage in Bactrocera dorsalis over Bactrocera tryoni – can the concept elucidate the invasive threat in northern Australia?

Incursions by exotic tephritids continue to threaten Australia. Host suitability for a specific tephritid is ranked by the number of adults which can emerge from one kg of fruit or the Host Reproduction Number (HRN). Bactrocera dorsalis has previously invaded northern Australia but was eradicated. However, Bactrocera dorsalis remains the largest exotic threat and is likely to invade through northern Australia but B. tryoni and other tephritids are already well established. One question is what hosts would likely provide the best early warning for an exotic incursion. Here, the HRN for 40 hosts for Bactrocera dorsalis and B. tryoni were established from the scientific literature. The reproductive advantages of one species over the other were calculated by dividing the higher HRN by the lower HRN. The fruits with the highest reproductive advantage (> 30) favouring B. dorsalis were soursop, mango and capsicum. The reproductive advantage estimate was compared to surveillance data collected during B. dorsalis eradication in north Queensland from 1995 to 1997. Mangoes and capsicum were among the mostly commonly infested hosts. Capsicums provided the second highest number of samples and would seem ideal candidates as sentinel plants for current surveillance programs. Some inconsistencies are identified and discussed. The HRN and reproductive advantage may have the potential to identify hosts and industries for early warning exotic fruit fly surveillance, better-targeted eradication programs and risk assessments for imports/exports. [ABSTRACT FROM AUTHOR]