Variation in egg mass scale thickness of three Spodoptera species and its effects on egg parasitoid performance.

Egg batches of Spodoptera moths are protected by scales deposited by females around and/or over eggs as a physical defense. These scales may affect the parasitism of some parasitoids, rendering biocontrol of Spodoptera eggs ineffective. In this study, we investigated the daily oviposition pattern of moths and the dynamics of egg mass scales of three Spodoptera species and examined the fitnesses of three potential egg parasitoid species to different egg mass scale thicknesses. The observations revealed that the three Spodoptera species share similar scale dynamics. From initial oviposition, S. exigua egg batches maintained a relatively high level of scale thickness (> 134.7 μm) for 2 days and S. frugiperda and S. litura for 3 days (> 105.9 μm, > 161.2 μm, respectively). During this period, the scales effectively hindered parasitism by Trichogramma species (parasitized 0.4%–14.9% eggs). Thereafter, the thickness of the scales decreased daily. The scales of the three Spodoptera species were all relatively thin (< 20.0 μm) after oviposition for 8 days, and subsequently, Trichogramma parasitized eggs more actively (parasitized up to 33.4%–36.5% eggs). Relatively, Trichogramma dendrolimi on S. frugiperda eggs, and Trichogramma chilonis on S. exigua eggs had higher parasitism. Meanwhile, Telenomus remus maintained a very stable and better performance than Trichogramma on Spodoptera species eggs with different scale thicknesses (parasitized 100% egg masses and 46.2%–60.0% eggs), which demonstrated its excellent potential as a Spodoptera species biocontrol agent. The findings elucidate the effect of egg mass scale thickness on effective parasitism by these egg parasitoid species and provide baseline information for the mixed use of Te. remus and Trichogramma against Spodoptera species. [ABSTRACT FROM AUTHOR]