Residential composting of infested fruit: A potential pathway for spread of Anastrepha fruit flies (Diptera: Tephritidae)

Authors: Kendra, Paul; HENNESSEY, MICHAEL - USDA-APHIS-PPQ-CPHST; Montgomery, Wayne; JONES, EDWARD - USDA-APHIS-PPQ-CPHST; Epsky, Nancy

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2007
Publication Date: 6/29/2007
Citation: Kendra, P.E., Hennessey, M.K., Montgomery, W.S., Jones, E.M., Epsky, N.D. 2007. Residential composting of infested fruit: A potential pathway for entry of Anastrepha fruit flies (Diptera: Tephritidae) into Florida. Florida Entomologist. 90(2):314-320.

Interpretive Summary: Tropical fruit flies (family Tephritidae) are serious economic pests whose larval stages feed inside host fruits, making detection of infestation difficult. If infested fruit is discarded by homeowners onto backyard compost piles, there is a potential risk of introducing or spreading insect pests. This study, a collaborative effort between scientists at the ARS Subtropical Horticulture Research Station (Miami, FL) and the APHIS Plant Epidemiology and Risk Analysis Laboratory (Raleigh, NC), was designed to simulate disposal of grapefruits infested with Caribbean fruit fly larvae on compost piles in south Florida. By comparing emergence of flies from fruit on outdoor compost piles relative to emergence from fruits held in the laboratory, it was estimated that an average of 10% of the females can survive composting conditions and potentially mate. This risk of pest introduction decreased with increasing compost temperatures, with mortality approaching 100% as compost temperatures rose above 48oC (118oF). Extension specialists can inform homeowners that pest survival can be reduced by burying produce deep and promoting high compost temperatures, including keeping piles moist and turning them often. The results obtained in this study can be used by scientists for quantitative risk analysis of a compost pathway for fruit fly introduction.

Technical Abstract: Composting of plant waste is a beneficial practice commonly used by American gardeners, but disposal of infested fruit directly into the environment creates a potential pathway for introduction of insect pests. This study was designed to estimate the likelihood of entry of exotic fruit flies (Tephritidae) into south Florida through residential composting. Ripe grapefruits, Citrus x paradisi Macfad., were infested with the Caribbean fruit fly, Anastrepha suspensa (Loew) and held in the laboratory until the larvae had reached the third instar. Half of the infested fruit was placed onto outdoor compost piles (10 replicate piles; 5 fruit per pile) and half was maintained under controlled laboratory conditions (10 replicate control bins; 5 fruit per bin). After fruit placement, compost piles were left exposed for 5 days to permit access of natural enemies and competitors, and then covered with screen cages. Adult fly emergence was recorded daily for the next 25 days from both the compost piles and control bins. Compost temperature, air temperature, relative humidity, and precipitation were monitored throughout the 30-day period, and the study was repeated four times under different seasonal conditions. Despite high mortality of flies from the composted fruit relative to control fruit, the overall risk of entry of a potentially mated female from composting of infested fruit was calculated to be ~10%. Of the environmental factors evaluated, compost temperature was found to have a significant effect on adult emergence. Mortality approached 100% in piles with maximum compost temperatures $48oC. The information presented in this report will provide experimental data in support of quantitative risk analysis for a tephritid-compost pathway.