Observations on the ecology of the rice-ear bug Leptocorisa oratorius (F.) (Hemiptera: Alydidae) in Sarawak (Malaysian Borneo).

Published online
01 Jul 1970
Content type
Journal article
Journal title
Journal of Applied Ecology

Rothschild, G. H. L.

Publication language
Borneo & Malaysia & Sarawak


The following is virtually the author's summary. Observations were made on the biology and ecology of Leptocorisa oratoria (F.) in Sarawak, mainly at Paya Paloh [cf. RAE A 58 2990], during a programme of research on various rice pests between 1964 and 1968. The mean duration of the life-cycle was 46 days (preoviposition period 21 days, egg stage 7 days and nymphal stage 18 days). The biological work included observations on oviposition and fecundity. The major part of the ecological work was concerned with the estimation of Leptocorisa numbers in the rice crop at regular intervals during several seasons to discover how population size was influenced by natural enemies, condition of the crop, and other factors. The numbers of Leptocorisa differed between varieties; short-term varieties supported larger numbers of immigrant adults than long-term varieties in 1968, but the reverse was true in 1967. Adult numbers varied from 1, 000 to 40, 000 per ac-1. Up to 200, 000 eggs were laid per acre, of which an average of 45% were destroyed by a Scelionid parasite, Gryon flavipes (Ashm.). Total losses between the egg and final nymphal instar were estimated to exceed 90%, of which arthropod predators were responsible for nearly half. The precipitin test showed that Gryllids (Anaxipha spp.) were the principal predators, but Tettigoniids (Conocephalus spp.) and two spiders, Eucta sp. and Argyope (Argiope) sp., also took appreciable numbers of Leptocorisa. There was evidence of heavy mortality of adult females before these had completed oviposition, but the cause could not be established. Sexually mature adults colonized rice fields when very little heading had occurred, but continued to lay eggs until the crop began to ripen. Nymphal mortality among late developers was high. During the off-season, small numbers of nymphs and adults of L. oratoria were found on self-sown or ratoon rice plants, and adults were found on. various grasses, including Echinochloa crusgalli.

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