Ionizing radiation as a phytosanitary treatment against fruit flies (Diptera: Tephritidae): Efficacy in naturally versus artificially infested fruit

Authors: Hallman, Guy; Thomas, Donald

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2010
Publication Date: 8/2/2010
Citation: Hallman, G.J., Thomas, D.B. 2010. Ionizing radiation as a phytosanitary treatment against fruit flies (Diptera: Tephritidae): Efficacy in naturally versus artificially infested fruit. Journal of Economic Entomology. 103(4):1129-1134.

Interpretive Summary: Some irradiation quarantine treatments for commercial use against fruits infested with tephritid fruit flies have been developed using artificial infestation of fruit without first testing the artificial techniques to determine if they might yield insects that are easier to control, thus result in a treatment that is not as effective as promised. In this study efficacy was compared using a common artificial technique (insertion of diet-reared larvae) with a commonly used more natural technique (placement of fruit in a cage with adults so that they lay eggs in the fruit which develop to larvae). The Mexican fruit fly, Anastrepha ludens (Loew), infesting grapefruit was the test insect. Both infestation techniques resulted in indistinguishable results, indicating that insertion of diet-reared third instar Mexican fruit fly into holes bored into grapefruit and subsequently sealed 24 h before irradiation adequately represents natural infestation. However, these results should not yet be extrapolated to the entire family of fruit flies without testing other species because this is the only direct comparison testing that has been done on any fruit fly.

Technical Abstract: Some phytosanitary irradiation treatments against tephritid fruit flies have been developed using artificial infestation of fruit without first comparing its effect on efficacy. In this study, efficacy was compared using infestation of grapefruit with Mexican fruit fly, Anastrepha ludens (Loew), via oviposition until larvae reached the late third instar vs. insertion of diet-reared third instars into holes made in grapefruits, 24 h prior to irradiation with 15-30 Gy. Both infestation techniques resulted in statistically indistinguishable results, indicating that insertion of diet-reared third instar Mexican fruit fly into holes bored into grapefruit and subsequently sealed 24 h before irradiation, would adequately represent natural infestation and could be used to develop a radiation phytosanitary treatment of the insect in grapefruit when prevention of adult emergence is used as the measure of efficacy. Dissection of puparia from non-irradiated insects that failed to emerge as adults showed a relatively even distribution of mortality among the developmental stages within the puparium. In contrast, dissection of puparia from irradiated third instars that did not emerge as adults revealed a sharp attenuation in development from cryptocephalic to phanerocephalic pupae demonstrating this transition to be the most affected developmental step for irradiated Mexican fruit fly third instars.