Irradiation of Colorado potato beetle eggs—effect on parasitism by the wasp Edovum puttleri

Abstract

Summary 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 2.5 x 104 and 5.0 x 106 rads prior to storage. For given storage times there were specific doses of radiation that resulted in notably, but not significantly, higher percent absolute emergence (number of adult wasps that emerged/total number of CPB eggs exposed to E. puttleri). After 7 days of storage, absolute emergence was highest after exposure to 2.5 x 104, 4.4 x 105 and 1.2 x 106 rads; and after 14 days of storage it was highest after exposure to 4.4 x 105 and 1.2 x 106 rads. For these doses of radiation and storage times, 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 72h to 14 days) in which CPB eggs are suitable hosts for rearing E. puttleri.