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馬尼拉小繭蜂Snellenius manila（Hymenoptera: Braconidae）防治秋行軍蟲Spodoptera frugiperda（Lepidoptera: Noctuidae）潛力評估之初探
Preliminary evaluation of the biocontrol potential of Snellenius manilae (Hymenoptera: Braconidae) against Spodoptera frugiperda (Lepidoptera: Noctuidae)
摘要
原產於美洲的秋行軍蟲（Spodoptera frugiperda（J. E. Smith, 1797））屬於鱗翅目（Lepidoptera）夜蛾科（Noctuidae）之多食性（polyphagous）害蟲，繁殖能力與遷徙能力強。此蟲於2019年6月入侵臺灣，國內已知受害作物包括玉米、高粱、落花生、水稻等9種。馬尼拉小繭蜂（Snellenius manilae（Ashmead, 1904））（Hymenoptera: Braconidae）為單元性幼蟲內寄生蜂（solitary larval endoparasitoid），以夜蛾科幼蟲為寄主，可寄生於秋行軍蟲之幼蟲。本研究目的為評估馬尼拉小繭蜂對秋行軍蟲之防治潛力，首先探討寄主齡期對馬尼拉小繭蜂寄生及發育表現之影響。結果顯示，一齡至三齡末的秋行軍蟲皆可被馬尼拉小繭蜂寄生，以二齡具有顯著較高之寄生率（76.64 ± 4.74%），一齡、三齡初及三齡末之寄生率分別為42.05 ± 5.42%、55.95 ± 3.76%及52.08 ± 3.85%。馬尼拉小繭蜂在一齡秋行軍蟲幼蟲上的未成熟期發育時間為15.6 ± 0.1日，顯著長於二齡 （14.9 ± 0.1日）、三齡初（14.8 ± 0.1日）及三齡末（15.0 ± 0.1日）；繭重則隨著秋行軍蟲齡期的增大而顯著增加，依序為三齡末（2.784 ± 0.024 mg）、三齡初（2.663 ± 0.021 mg）、二齡（2.536 ± 0.019 mg）及一齡（2.507 ± 0.022 mg）。再根據以上結果，選用二齡秋行軍蟲幼蟲進行盆栽試驗，以了解馬尼拉小繭蜂防治寄主植物上之秋行軍蟲的效果。結果顯示，寄生率在人工飼料（61.01 ± 8.47%）上與玉米（38.58 ± 3.43%）及花生（37.01 ± 4.71%）植株上無顯著差異；化繭率於人工飼料為93.86 ± 1.68%，於玉米（100.00 ± 0.00%）及花生（99.43 ± 0.57%）植株之處理組顯著較高。除此之外，馬尼拉小繭蜂於取食玉米植株之秋行軍蟲之未成熟期發育時間為13.8± 0.1日，顯著短於取食人工飼料（14.6 ± 0.1日）與花生植株（15.3 ± 0.2日）。綜上所述，馬尼拉小繭蜂對秋行軍蟲具有防治潛力，對於寄主植物上之秋行軍蟲仍有寄生效果，且二齡幼蟲為最佳寄生齡期。
並列摘要
The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a lepidopteran insect of the family Noctuidae native to the Americas. It is a highly polyphagous insect with a high reproductive rate and good migratory capacity. In June 2019, the larvae of S. frugiperda was first observed in Taiwan. So far, S. frugiperda has caused damage to nine plant species in Taiwan, including corn, sorghum, rice, peanut, and other crops. Known as a solitary larval endoparasitoid of the Noctuidae family, Snellenius manilae (Hymenoptera: Braconidae) can parasitize the larvae of S. frugiperda. To evaluate the biocontrol potential of S. manilae against S. frugiperda, this study first investigated the effect of host larval instar on the parasitism and performance of S. manilae. The results revealed that S. manilae could parasitize S. frugiperda larvae from the first instar to late third instar. The parasitization rate on second instar larvae was significantly higher than on the other instars, which were 42.05% ± 5.42%, 55.95% ± 3.76%, and 52.08% ± 3.85% on the first, early third, and late third instars, respectively. The immature developmental time of S. manilae on the first instar larvae (15.6 ± 0.1 days) was significantly longer than that on the second instar (14.9 ± 0.1 days), early third instar (14.8 ± 0.1 days), and late third instar (15.0 ± 0.1 days). The cocoon weight increased significantly with host instar stage. The cocoon weight on the first, second, early third, and late third instars were 2.507 ± 0.022, 2.536 ± 0.019, 2.663 ± 0.021, and 2.784 ± 0.024 mg, respectively. On the basis of the results, second instar larvae were assigned to the subsequent pot experiments to understand the control efficacy of S. manilae against S. frugiperda on host plants. No significant differences were observed in the parasitization rates of S. manilae on S. frugiperda larvae fed with an artificial diet (61.01% ± 8.47%), corn host plants (38.58% ± 3.43%), or peanut (37.01% ± 4.71%) host plants. The cocoon rate of S. manilae was significantly higher on S. frugiperda larvae fed with corn (100.00% ± 0.00%) or peanut (99.43% ± 0.57%) host plants. Additionally, the immature developmental time of S. manilae was significantly shorter on S. frugiperda larvae fed with corn host plants than those fed an artificial diet (14.6 ± 0.1 days) or peanut (15.3 ± 0.2 days) host plants. In conclusion, S. manilae demonstrated biocontrol potential against S. frugiperda and retained a parasitic effect against S. frugiperda when feeding on host plants. The second instar was the most suitable host stage for S. frugiperda biological control when using S. manilae.