Submitted to: Invertebrate Reproduction and Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 15, 2000
Publication Date: N/A
Interpretive Summary: The Colorado potato beetle is one of the most destructive insect pests of potato, tomato and eggplant crops in North America and Europe costing growers hundreds of millions of dollars each year. Edovum puttleri, a parasitic wasp, has been shown to be an effective biological control agent for managing populations of Colorado potato beetles on eggplant. However, a constant supply of large numbers of healthy CPB eggs is required to produce the quantities of wasps that would be needed for mass rearing and release programs. The current study was undertaken in order to develop a method for storing CPB eggs and maintaining them in a state that was suitable for parasitization by, and development of, E. puttleri. Exposure of eggs to gamma radiation, as a means of preservation, was evaluated. A variety of doses, storage times and storage conditions were tested. We report here that irradiation can extend the period of time in which CPB eggs remain in good condition (i.e., are capable of being parasitized, wil support the growth and development of the wasp and will produce viable adult wasps) from 72 h to 14 days. Although depending on radiation dose and storage time, storage of irradiated eggs had a somewhat negative effect on percent parasitization, it enhanced the percentage of adult wasps that emerged from parasitized eggs. Irradiation has been shown to be useful for food preservation and thus could easily be adapted for treatment of large numbers of CPB eggs. In addition to providing a method for using gamma radiation to preserve CPB eggs, our results have laid the foundation for additional studies designed to extend the storage time for which irradiated eggs can serve as suitable hosts for biological control agents such as parasitic wasps.
Technical Abstract: In order to extend the period of time during which Colorado potato beetle (CPB) eggs are suitable hosts for the parasitic wasp Edovum puttleri, CPB eggs were subjected to various doses of gamma radiation between 25 kilorads and 5 megarads prior to storage. Percent absolute adult emergence (number of adult wasps that emerged/total number of CPB eggs exposed to E. puttleri) was not correlated with dosage, but rather for given storage times, there were specific doses of radiation that resulted in notably higher absolute emergence. After exposure to 436 krads and 1.17 megarads and 7 or 14 days of storage, percent absolute emergence was equal to 40 +/- 8%, a value that overlaps the range reported for CPB eggs that have not been irradiated. With increased storage time, absolute emergence dropped below 25%. While storage of irradiated eggs had a negative effect on percent parasitization, it did not affect the percentage of wasps that emerged (percent emergence = number of adult wasps that emerged/number of CPB eggs that were parasitized) from parasitized eggs. Percent emergence from non-irradiated eggs has been reported to average 78%, while in these studies, percent emergence from irradiated eggs typically was greater than 90%. Irradiation and storage of CPB eggs had little effect on the weights of adult wasps, and these wasps appeared to be active and in good condition. However, for unfed adult wasps, longevity decreased with increasing doses and storage times. Gamma irradiation of CPB eggs can be used to kill developing CPB embryos and to prevent deterioration of the host eggs. Our results show that irradiation can increase the period of time (from 72 h to 14 days) in which CPB eggs are suitable hosts for rearing E. puttleri.