Capacity of Chelonus formosanus to parasitize the eggs of Spodoptera frugiperda, and the morphology of the antennal sensilla of C. formosanus as revealed by scanning electron microscopy

Author of the article:JIA Jing-Jing1** CAI Qiu-Jiu2 HUANG Wei-Kang1 FENG Qing1 LIN Zhu-Feng1 JI Xun-Cong1***

Author's Workplace：1. Institute of Plant Protection, Hainan Academy of Agricultural Sciences, Research Center of Quality Safety and Standards for Agro-Products, Hainan Academy of Agricultural Sciences, Key Laboratory of Plant Disease and Pest Control of Hainan Province, Haikou 571100, China; 2. College of Plant Protection, Hainan University, Haikou 570228, China

Key Words： Chelonus formosanus; Spodoptera frugiperda; parasitic capacity; antennal sensilla

Abstract： [Aim]  To assess the capacity of the wasp Chelonus formosanus to parasitize Spodoptera frugiperda eggs, and to describe the basic antennal structure and sensilla of this species. [Methods]  The search and the processing time of S. frugiperda eggs by C. formosanus, with, and without, parasitic experience, were observed in an intelligent, artificial climate chamber [(26±2) ℃, RH 70±10%, 12L∶12D] at different C. formosanus densities. The proportion of S. frugiperda eggs parasitized was evaluated using the caging method. The antennal structure of adult, male and female C. formosanus was observed under digital, and scanning, electron microscopy. [Results]  C. formosanus with prior oviposition experience required less time to find S. frugiperda eggs than inexperienced individuals, and was also shorter at lower C. formosanus densities. The most significant difference in search time was, however, between adult female C. formosanus with, and without, previous oviposition experience (P＜0.05). The average time required by C. formosanus to process 100, 200 or 300 eggs S. frugiperda eggs was (38.44±1.99), (75.99±3.24) and (103.71±6.21) min, respectively. The number of parasitized S. frugiperda egg masses increased with increasing C. formosanus density, and there were significant differences in the number of egg masses parasitized at densities of 1, 3 and 5 C. formosanus females (P＜0.05）. The antennal length of females was obviously shorter than that of males (P＜0.05）, with the flagellum of females consisting of 22 or 23 subsections c.f. 24 to 27 subsections in males. Ten morphologically distinct types of sensilla were observed on the antennae; sensilla trichodea, sensilla placodea, sensilla basiconca, sensilla chaetica, sensilla squamiformia, sensilla coeloconica, sensilla campaniformia and sensilla cavity. Böhm bristles, cuticular pores and sensilla trichoidea were the main sensory organs, being both the most abundant and widely distributed, followed by the sensilla placodea. [Conclusion]  Previous oviposition experience has a significant effect on the time required by adult female C. formosanus to find host eggs. The time required to process eggs increases with host egg density and the parasitism rate of a single egg mass of S. frugiperda can reach 100%. The antennae of C. formosanus have a total of 10 sensory receptors.