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144

9.5 Biological Control in Vegetable Pest Management in Tropical Asia: Where Do We Currently Stand?

R. Srinivasan1, M-Y. Lin2, N.T.T. Hien3 and V.M. Hai4

1World Vegetable Center, Shanhua, Tainan, TAIWAN, [email protected], 2World Vegetable Center, Shanhua, Tainan, TAIWAN, [email protected], 3Plant Protection Research Institute, Tu Liem, Ha Noi, VIETNAM, [email protected], 3Vietnam Academy of Agricultural Sciences, Thanhtri, Ha Noi, VIETNAM, [email protected]

Vegetable including Chinese , L. var. pekinensis, pak-choi, B. rapa var. chinensis, choisum, B. rapa var. parachinensis, and Chinese , B. oleracea L. var. alboglabra (), are among the most important vegetables in Asia. Production of vegetable brassicas is constrained by a plethora of pests including diamondback , Plutella xylostella L. (: Plutellidae), cabbage head caterpillar, pavonana Fabricius (Lepidoptera: ), cabbage web worm, Hellula undalis Fab. (Lepidoptera: Crambidae), imported cabbage worm, Pieris rapae L. (Lepidoptera: Pieridae), aphids, Myzus persicae Sulzer, Lipaphis erysimi Kaltenbach, and Brevicoryne brassicae L. (Hemiptera: Aphididae) and flea beetles, Phyllotreta spp. (Coleoptera: Chrysomelidae) in tropical Asia. However, P. xylostella can be brought under reasonable control with the introduced larval parasitoid, Diadegma semiclausum Hellen (Hymenoptera: Ichneumonidae) in highlands. Performance of D. semiclausum is complemented by the pupal parasitoid, Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae), another classical bio-control agent in the Asian highlands. Cotesia plutellae Kurdjumov (Hymenoptera: ), the predominant larval parasitoid in lowland brassica production systems offer significant control of P. xylostella. Hence, World Vegetable Center (WorldVeg) took a lead in expanding the introduction of these bio-control agents against P. xylostella in tropical Asia for the past four decades. However, absence of effective bio-control agents targeting the secondary lepidopterans still triggers the brassica producers to rely more on chemical pesticides, which actually disrupts the biological control of P. xylostella and thus leading to the resurence of this pest (Talekar, 2004). In addition, absence of an effective pupal parasitoid, which can complement C. plutellae also leads to pesticide overuse on brassicas in Asian lowlands. Hence, there is an urgent need to expand the bio-control options against major insect pests of vegetable brassicas in Asia. Identification of a heat tolerant strain of D. semiclausum in Syrian lowlands (Kadirvel et al., 2011) has opened up new avenues for P. xylostella management in lowland vegetable brassica production in rest of Asia. This strain was collected from the lowland areas of Homs, Syria (about 203-487 m above sea level) and it thrived well when the parasitized P. xylostella larvae were reared at day and night temperatures of 35°C and 20°C, respectively. Similarly, identification of an arrhenotokous population of the generalist egg parasitoid,

©CAB International 2017. Proceedings of the 5th International Symposium on Biological Control of (eds. P.G. Mason, D.R. Gillespie and C. Vincent) Session 9: Biocontrol in Vegetable Brassica Pest Management – R. Srinivasan et al. (2017) 145

Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) parasitizing C. pavonana egg masses to a maximum extent of 87% in Samoa (Uelese et al., 2014) enhances the potential for biological control of C. pavonana elsewhere. During 2014-2016, we conducted random and sporadic surveys in vegetable brassica fields in Taiwan and Vietnam to identify the occurrence of parasitoids on secondary lepidopterans and the sucking pests. The results from our surveys confirmed the larval parasitoid, Cotesia glomerata L. (Hymenoptera: Braconidae) (Fig. 9.5.1) and a pupal parasitoid, Pteromalus puparum L. (Hymenoptera: Pteromalidae) (Fig. 9.5.2) as major parasitoids of P. rapae. Similarly, Diaeretiella rapae McIntosh (Hymenoptera: Braconidae) was found to be the major parasitoid of aphids on brassicas in Vietnam. Although D. rapae parasitises about 98 species of aphids infesting more than 180 plant species belonging to 43 plant families distributed in 87 countries, the most preferred host are brassica aphids including B. brassicae, M. persicae and L. erysimi (Singh and Singh, 2015). Hence, these natural enemies increase the scope of brassica bio-control programs in tropical Asia. Thus, conservation and/or augmentation of various bio-control agents against P. xylostella as well as secondary lepdiopterans on vegetable brassicas in tropical Asia have become imperative to reduce the pesticide misuse. In addition, bio-pesticides including Bacillus thuringiensis (Srinivasan, 2012) and sex pheromone lures (Zhao et al., 2011) can enhance the performance of natural enemies and thus offering integrated pest management options for safer brassica production in tropical Asia.

Fig. 9.5.1. Cocoons of Cotesia glomerata on Pieris rapae cadaver.

146 Session 9: Biocontrol in Vegetable Brassica Pest Management – R. Srinivasan et al. (2017)

Fig. 9.5.2. Adults of Pteromalus puparum parasitizing Pieris rapae pupa.

Acknowledgements: We thank the Federal Ministry for Economic Cooperation and Development, Germany for financing this study. We also gratefully acknowledge the Natural History Museum, UK, for identifying the parasitoid species.

References

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