关键词: 草地贪夜蛾, 螟蛉盘绒茧蜂, 寄主幼虫龄期, 产卵次数, 生物防治

Abstract: 【Aim】 To evaluate the parasitism potential of Cotesia ruficrus, an indigenous parasitic natural enemy, against the larvae of Spodoptera frugiperda, a major invasive agricultural pest. 【Methods】The parasitism preference of the mated 24 h-old female adults of C. ruficrus to the 1st-3rd instar larvae of S. frugiperda was performed by selection test. The developmental duration, numbers of cocoons, eclosion rates, sex ratios (proportions of females), adult longevity and adult size of the offspring of C. ruficrus were determined when its mated 24 h-old female adults parasitized the 1st, 2nd or 3rd instar larvae of S. frugiperda, respectively, by non-selection test. The oviposition times of the mated 24 h-old female adults of C. ruficrus on the 2nd instar larvae of S. frugiperda were determined by the direct observation method, and then the effects of different oviposition times on the developmental duration, number of cocoons, eclosion rate, sex ratio, adult longevity and adult size of the offspring of C. ruficrus were measured. The parasitic functional response of the mated 24 h-old female adults of C. ruficrus to the 2nd instar larvae of S. frugiperda was determined with small-leaf dish method. 【Results】 When the mated 24 h-old female adults of C. ruficrus parasitized the 1st-3rd instar larvae of S. frugiperda, the parasitism rates, egg-larval duration, pupal duration, numbers of cocoons per host, eclosion rates, and proportions of females of C. ruficrus were 34%-54%, 8.7-9.9 d, 3.9-4.1 d, 19.7-41.2 cocoons, 84.4%-92.0% and 31.5%-38.8%, respectively, and the female adult size of the offspring was larger than the males. The female adult longevity of the offspring of C. ruficrus was significantly longer than that of the males when the 1st or 3rd instar larvae of S. frugiperda were parasitized. The oviposition times of the mated 24 h-old female adults of C. ruficrus on the 2nd instar larvae of S. frugiperda had a significant effect on the biological characters of the offspring of C. ruficrus. With the increase of the oviposition times, the male adult longevity of the offspring of C. ruficrus was shortened, and the male adult size of the offspring became smaller. Compared with parasitization once, after the 2nd instar larvae of S. frugiperda were parasitized by the mated 24 h-old female adults of C. ruficrus for three times, the egg-larval duration of the offspring of C. ruficrus was significantly prolonged by 0.7 d, the pupal duration was shortened by 0.4 d, the number of cocoons per host significantly increased by 25 and the proportion of females significantly decreased by 58.8%. The parasitic functional response of the mated 24 h-old female adults of C. ruficrus to the 2nd instar larvae of S. frugiperda was Holling Ⅱ type, the daily maximum parasitic number was 17.5, the instantaneous attack rate was 0.043 and the average handling time was 1.368. 【Conclusion】 This study evaluated for the first time the biological control potential of C. ruficrus against S. frugiperda larvae, and indicated that the parasitoid was an effective native natural enemy of S. frugiperda, providing technical reserves and theoretical basis for further utilizing local natural enemies to control invasive pests.

Key words: Spodoptera frugiperda; Cotesia ruficrus, host larval instar, oviposition times, biological control