How Fecund is Lymantria xylina Swinhoe (Lepidoptera: Lymantriidae) in Taiwan?

Abstract

The casuarina moth Lymantria xylina is one of the most damaging pests in the casuarina windbreaks of Taiwan proper and on surrounding islands. This study aimed mainly to understand the fecundity of the casuarina moth, geographical variations in fecundity and in measurements of the egg mass, and the impact of egg parasitoids on the fecundity of this species. In total, 360 egg masses were collected from 12 casuarina plantations along the west coast of Taiwan and on Penghu Island. The number of eggs laid by the female casuarina moth varied from 180 to 1544 per egg mass, with an average of 592.5±213.8. The mean number of eggs per mass varied significantly among sites. The average length of egg masses was 36.2±10.3 mm, and the average width of egg masses was 9.3±1.8 mm. The size of egg masses also varied significantly between sites. The longer the egg mass was, the wider the egg mass was, and the greater number of eggs there were per mass. However, longer egg masses were narrower, while shorter egg masses were wider. Egg masses on larger branches had more eggs. About 1/3 (122/360) of the collected egg masses were attacked by the egg parasitoid, Ooencyrtus kuvanae (Hymenoptera: Encyrtidae). A total of 855 egg parasitoids emerged from these 122 parasitized egg masses. The average number of egg parasitoids emerging per mass was 7.1±6.0. No significant difference in the number of egg parasitoids was found among sites on which more than 10 parasitized egg masses were found. The low rate (0.4%) of egg parasitization by O. kuvanae in this study is discussed. However, the real impact of O. kuvanae on the fecundity of casuarina moth and the potential usefulness of O. kuvanae to control the casuarina moth in Taiwan require further evaluation.