Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2011
Publication Date: 12/2/2011
Citation: Thomas, D.B., Hallman, G.J. 2011. Developmental arrest in Mexican fruit flies (Diptera: Tephritidae) irradiated in grapefruit. Annals of the Entomological Society of America. 104:1367-1372. Interpretive Summary: Fresh fruit imported to the USA must undergo inspection and treatment to ensure that it is free of insect pests, such as fruit fly worms. Radiation treatment is effective but does not kill such worms outright. They die later. This is a problem for inspectors who would normally reject a shipment with live worms. At present, they rely on paperwork which certifies that the fruit has been irradiated. In this research, we dissected thousands of irradiated insects in order to identify the damage caused by the radiation. Based on this research, we suggest a test that inspectors can use to check if the insects have been irradiated by looking for the characteristic damage. Basically, irradiated worms develop into a fly that is headless. This damage, lack of a head, can be seen in the pre-adult stage.
Technical Abstract: Irradiation provides an alternative to fumigation and temperature based treatments as a disinfestation method for fresh fruit commodities. A disadvantage of irradiation is that the induction of pest mortality is delayed. Consequently, the presence of live pests in the commodity would not be evidence of treatment failure, as it would with all other disinfestation methods in commercial use. Mortality from a radiation treatment typically ensues during a major developmental transition, usually one involving ecdysis. Thus early instars fail to develop into later instars or to pupariate. Over a range of sublethal doses of gamma radiation applied to third instar Mexican fruit flies infesting grapefruits, the great majority of treated larvae arrest development at pupal ecdysis, the transformation from a cryptocephalic to a phanerocephalic pupa. More than 99.9 percent of treated larvae die at or prior to reaching this transition at the highest dose tested (30 Gy). Contrary to expectations, the radiation treatment did not cause atrophy of the imaginal tissues, a result that we attribute to the phenomenon of apoptosis. The utility of a quarantine bioassay based on the detectable attributes of radiation pathology is discussed.