Suitability of false codling moth eggs from different sterile to fertile moth ratios in the sterile insect technique programme, to parasitism by Trichogrammatoidea cryptophlebiae

Abstract

The sterile insect technique (SIT) and augmentative releases of egg parasitoids, Trichogrammatoidea cryptophlebiae have been employed to manage false codling moth (FCM), Thaumatotibia leucotreta in South Africa. To enhance FCM control, simultaneous releases of sterile moths and egg parasitoids are conducted. It is, therefore, necessary to determine the compatibility and combined values of these approaches. A laboratory study was conducted to explore the susceptibility of FCM eggs resulting from various pairings of sterile and fertile moths to parasitism by egg parasitoids. The ratios of sterile to fertile FCM used in the study were 0:1, 10:1, 20:1, 40:1, and 60:1. The fitness of the egg parasitoids emerging from these ratios was assessed using a flight chamber test. Sterile male and female FCM treated with 150 Gy of gamma irradiation were crossbred with fertile counterparts. The resulting eggs were then exposed to egg parasitoids for parasitism. The study evaluated the parasitism rates of newly laid (24 h), 48 h and 72 h old eggs. Overall, eggs from all ratios were suitable for egg parasitoid development and acceptable for oviposition. Significantly higher proportions of parasitised eggs were recorded between the control (0:1) and ratios 40:1 and 60:1 with 48 h old eggs. Additionally, a higher number of egg parasitoids emerged across the ratios, with a higher proportion of female-to-male parasitoids recorded. These findings indicate that egg parasitoids can successfully accept and hatch from FCM eggs from different sterile to fertile moth ratios. This suggests the potential for achieving a synergistic suppressive effect by combining SIT and augmentative releases of egg parasitoids for improved FCM control. Nevertheless, further studies are necessary to investigate the combined releases of sterile moths and parasitoids under field conditions.