INVERTEBRATE PESTS OF ORCHIDS IN SINGAPORE

Abstract

A general survey of the invertebrate orchid- peets in Singapore was carried out from April 1966 to July 1968. 12 nurseries and 30 other localities covering 2/3 of the postal districts of Singapore were visited.

37 species of orchid pests are now known to occur in Singapore. Of these 29 are insects, 5 are slugs and snails, 2 are nutes and 1 is a nematode. About a third of the insects, the slugs and snails and the mites are comraonly di stributed. Another third of the insects and the nematodes have a fairly common distribution while the remaining third of the insects are occasional pests. Only some of the 37 species are host specific while many are known to attack orchids as well as other plants. The form of a flower or a leaf is an important factor for pest susceptibility and may explain why many of the pests prefer certain orchid genera. However, specificity to a particular species of orchids has so far not been observed.

The result s of the ecological studies on Chliaria tora semanga Corbet and Agonita .sp. indicate that the infestation frequency of the C. t . semanga is positively correlated with the density of the flower sprays in a garden while the population of Agonita sp. is enhanced by the daily length of sunshine but adversely affected by a rainy period.

For life- history study the breeding of 4 different species Lema pectoralis Baly, Chliaria tora semanga Corbet, Anaphothrips corbetti Priesner and Tenuipalpus pacificus Baker -- proved successful under air-conditioned laboratory and room temperature . Attempts were also made on Agonita sp. and Parlatoria proteus (Curtis) but have not been totally successful due to the difficulties in recording their larval instars. In L. pectoralis, the anterior gut is probably the source of the cocoon material. An attempt to gather some information on 3 common pests, C. tora semanga, L. pectoralis and Agonita sp. through the distribution of questionnaires has not been altogether successful but certain useful informations with regard to the type of pest present, its degree of infestation, seasonal occurrence and hust-range and the type of pesticide used were obtained. From these a general measurement of the value of the pesticides could be estimated by comparing pests found and pesticides used in the particular places. It is found that sevin insecticide and Agrocide 26 ' are effective for chewing pests (e. g. caterpillar, beetle larva etc.); systemic insecticide such as Roger & Roxion are effective for sucking insects (e.g. aphide scales, thrips etc.) and miticides containing kelthane or tedion provide excellent control on mites. Parasites and predators serve as means of biological control especially those collected from the scales are identified and recorded here. A new species of Encyrtidae, Anusioidea phoonae Tackikawa 1968 was collected from Singapore.