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THE BIOLOGY OF THE TWO COMMON STORAGE SPECIES OF ORYZAEPHILUS (COLEOPTERA, CUCUJIDAE)

1956; Wiley; Volume: 44; Issue: 2 Linguagem: Inglês

10.1111/j.1744-7348.1956.tb02127.x

1744-7348

Robert W. Howe,

Insect Resistance and Genetics

Oryzaephilus surinamensis (L.) and O. mercator (Fauv.) are distinct species which do not interbreed; they can be distinguished by the relative lengths of eye and temple and by the male genitalia. Both species are imported into Britain, O. surinamensis chiefly on cereal products and O. mercator chiefly on oilseed products. O. mercator is killed by cold in Britain, but O. surinamensis can survive and not infrequently becomes a pest. Eggs hatched at temperatures from 17·5 to 40°C. Egg mortality was high below 20°C. and above 37·5°C. Low humidity also increased egg mortality but did not affect the length of the instar which was shortest at 35°C. and above. On wheat‐feed, the larva of O. mercator grew more slowly than that of O. surinamensis and was more sensitive to low humidities. The optimum for O. mercator was about 30–32·5°C. and that for O. surinamensis about 3–35°C. Low humidity increased the length of the larval period, and at 10% R.H., O. mercator died outside the range 25–32·5° C. The shortest pupal period was observed at over 35°C. On coconut meal at 30°C. and 70% R.H., O. mercator grew faster than O. surinamensis , which could not grow on this food at lower humidities. O. mercator grew more slowly on this food than on wheatfeed. Neither species completed development on groundnut meal unless yeast powder was added. The usual number of larval moults before pupation was three, but a few individuals had four or two. The longer larval period of O. mercator is explained partly by the individual instars being slightly longer than in O. surinamensis and partly by the increased tendency for the latter species to have only two larval moults. The preoviposition period of both species at 30 and 33°C. was 3–8 days, usually about 5. O. mercator reached a peak of three eggs per female per day and O. surinamensis of 6–10 per female per day by the end of a week and maintained these rates for a month, laying about 200 and 375 eggs per female respectively. About 95% of eggs hatched. Both species can increase rapidly in the tropics, but neither can grow very quickly in unheated stores in Britain. O. surinamensis is a pest because it can survive in large numbers in the fabric of warehouses and multiply rapidly when warm or actively heating produce becomes available.