From trickle to flood: the large-scale, cryptic invasion of California by tropical fruit flies

Nikos T Papadopoulos,Richard E Plant,James R Carey

doi:10.1098/rspb.2013.1466

Abstract

Since 1954, when the first tropical tephritid fruit fly was detected in California, a total of 17 species in four genera and 11 386 individuals (adults/larvae) have been detected in the state at more than 3348 locations in 330 cities. We conclude from spatial mapping analyses of historical capture patterns and modelling that, despite the 250+ emergency eradication projects that have been directed against these pests by state and federal agencies, a minimum of five and as many as nine or more tephritid species are established and widespread, including the Mediterranean, Mexican and oriental fruit flies, and possibly the peach, guava and melon fruit flies. We outline and discuss the evidence for our conclusions, with particular attention to the incremental, chronic and insidious nature of the invasion, which involves ultra-small, barely detectable populations. We finish by considering the implications of our results for invasion biology and for science-based invasion policy.

Highlights

Tropical fruit flies (Tephritidae), such as the Mediterranean fruit fly (Ceratitis capitata) from Africa, the oriental fruit fly (Bactrocera dorsalis) from Asia and the Mexican fruit fly (Anastrepha ludens) from the Americas, are recognized by entomologists as among the most destructive agricultural insect pests in the world [1,2]
Several lines of evidence support the hypothesis that from five to nine tephritid species have become self-sustaining populations in the state: their abrupt first appearance in the mid-1950s followed by high incidence of repeat detections, their marked seasonality and northward spread, the lack of new detections and/or introductions of new species in most other at-risk regions in the USA and Mediterranean Basin, and the high probabilities of repeatedly detecting many of the tephritid species in California while at the same time not detecting them in other at-risk areas
These legal criteria are required for regulatory compliance to enable growers to ship their produce, our results reveal that the more stringent ecological requirements for eradication declaration were not met in the majority of cases

Summary

Introduction

Tropical fruit flies (Tephritidae), such as the Mediterranean fruit fly (Ceratitis capitata) from Africa, the oriental fruit fly (Bactrocera dorsalis) from Asia and the Mexican fruit fly (Anastrepha ludens) from the Americas, are recognized by entomologists as among the most destructive agricultural insect pests in the world [1,2]. Because of tephritids’ economic importance, US states such as California—considered by both the US Department of Agriculture (USDA) and the California Department of Food and Agriculture (CDFA) to be free of these pests, but with climates favourable to their establishment—invest heavily in measures to keep tephritids from becoming established These steps include restricting importation of commodities that originate in regions with ongoing tephritid outbreaks, requiring post-harvest treatments for imported fruits and vegetables grown in areas where the pests are endemic or established, maintaining large-scale monitoring programmes for early detection, supporting preventive release programmes of sterile flies to pre-empt establishment, and launching eradication campaigns to eliminate pest populations once discovered. We discuss both scientific and practical implications of these findings

Methods

Results

Findings

Discussion

Conclusions