Field Control Effect of ITelenomus remus/I Nixon and ITrichogramma chilonis/I Ishii Compound Parasitoid Balls against ISpodoptera frugiperda/I

Spodoptera frugiperda is a devastating agricultural pest. Telenomus remus is an efficient egg parasitoid wasp for the control of S. frugiperda, but it has a limited host range and is expensive in application. In this manuscript, we combined Trichogramma chilonis, an easily available and cheap egg parasitoid wasp, with Te. remus in different ratios to form compound parasitoid balls and released them into a maize field to investigate their control efficacy against S. frugiperda. We found that compound parasitoid balls were more effective in the control of S. frugiperda than the release of only a single egg parasitoid wasp (Te. remus or Tr. chilonis). Moreover, the control effect against S. frugiperda could still retain more than 50% in the treatment, with 80% Te. remus and 20% Tr. chilonis and that with 20% Te. remus and 80% Tr. chilonis after 15 days of the release and given the higher cost of production of Te. remus, we concluded that the combination of 20% Te. remus and 80% Tr. chilonis was a more cost-efficient ratio for the control of S. frugiperda. Although the release of egg parasitoids has proven to be an effective strategy for the control of the fall armyworm (FAW), a single egg parasitoid, however, has exposed some deficiencies in practice, and it is worthwhile to explore whether the combination of multiple parasitoid species released can be used to control FAW by adopting an inter- or intra-specific relationship. In this study, we released compound parasitoid balls of Te. remus and Tr. chilonis in maize fields to explore the effects of combinations in different proportions of these two egg parasitoids on the control of the FAW. The results showed that the release of compound parasitoid balls improved the control effect on the FAW compared to the release of only Te. Remus (100%) and only Tr. Chilonis (100%). The treatments released with compound parasitoid balls significantly increased the egg parasitism rate against the FAW, reduced its populations, and alleviated its damage to maize as compared to the treatment with only Tr. chilonis (100%) released, whereas there was no significant difference in the egg parasitism rate and FAW populations between the treatments with the release of only Te. remus (100%) and that of compound parasitoid balls. Among the compound parasitoid balls with different proportions of egg parasitoids, the treatment with 80% Te. remus and 20% Tr. chilonis and that with 20% Te. remus and 80% Tr. chilonis could still retain mor