Bionomics of cabbage caterpillars in the midcountry of Sri Lanka with special reference to diamondback moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae) [Abst]

Bionomics of cabbage caterpillars in the midcountry of Sri Lanka with special reference to diamondback moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae) [Abst]

Postgraduate Institute of Agriculture of the University of Peradeniya Sri Lanka

1992

2p.

REP.DBM-2070

Laboratory and field investigations were carried out under insecticide free conditions to study the bionomics of lepidopteran pests of cabbage grown in mid-country of Sri Lanka. The major pests were Plutella xylostella L., Spodoptera litura F., Crocidolomia binotalis Z., Chrysodeixis eriosoma Doubl. and Hellula undalis Fab. The life history, external morphology, behaviour and damage caused by each species were stuidied. Observations were also made on degree of infestation of immature stages in respect of age and inhabiting sites of plants and the season. The lifespan of respective species ranged from 15.7 - 27.2 (mean=18.4), 28.40 - 42.92 (mean=32.48), 20.93 - 42.83 (mean=28.57), 19.83 - 37.43 (mean=25.81) and 16.35 -35.81 (mean=25.6) days. Two keys were developed to differentiate the eggs and larvae of the different species in the field. The damage done by a density of 1 - 2 larvae per plant of H. undalis and S. litura prevented the establishment of young plants and therefore was more severe than that of other species. Plutella xylostella, S. litura and C. binotalis were more predominant than other species. The population of H. undalis peaked during the period from March to July. Higher temperature, relative humidity and lower day temperature variation seemed to favour its abundance. Populations of other caterpillars were severe from December to April and at a lower rate from mid July to October. Higher incidences were associated with weater conditions such as lower temperature and relative humidity and a higher day temperature variation after a period of higher temperature and Seventeen species of parasitoids were observed to parasitize cabbage caterpillar species. Major species included Trichoqrammatoidea? bactrae (caused up to 35% egg parasitism), Apanteles plutellae Kurdjumov (caused up to 51% larval parasitism) and Tetrastichus species (caused up to 25% pupal parasitism) on P. xylostella, Telenomus remus Nixon and Microplitis sumilis Lyle on S. litura, Apanteles stantoni Ashemad on C. binotalis, Apanteles ruficrus Halidae on C. eriosoma and Diaeratiella rajpae M'Intosh on H. undalis. All the parasitoids exhibited seasonal occurrences. Hyperparasitism by Tetrastichus sokolwskii Kurdjumov and Aphanoqmces fijientis Ferr. was observed on A. plutellae and their occurrences were occasional. All these information will be useful to develop Integrated Pest Management strategy (IPM) for cabbage. [AS]

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