Diapause In the Maize Stemborer1

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Abstract
Diapausing larvae of Busseola fusca (Fuller) occur throughout most of the year, even when maize is actively growing. Diapause was recorded in June, reached the peak in July, and completed in September. The least number of larvae was obtained in October. There was a buildup again of diapausing larvae from November, with the peak in December. Diapause development in the November-December generation was completed about february-March of the following year. The fact that some of the larvae of B. fusca go into diapause at each generation, irrespective of the state of the maize plants, suggests a probable genetic mechanism or heredity. Some morphological and physiological factors such as coloration, molting frequency, loss in weight, and feeding activities associated with diapause in the insect were studied. Pigmented (nondiapausing) larvae of B. fusca occurrcd most abundantly when maize plants were either young or mature but still fresh, while the nonpigmented (diapausing larvae) occurred at those times of the year when the maize stems were dry in the field. Most of the larvae collected in October and November were pigmented; only 11.6% collected in October and 43.6% collected in November were diapausing larvae. Therefore, diapause may not, after all, be responsible for the coloration of the larvae of B. fusca . Diapausing larvae of B. fusca molted up to 6 times during the period of diapause and progressively decreased in weight at the rate of 7.4 mg/week. Diapausing larvae of B. tusca fed throughout the period of diapause, but the rate of feeding activity (when compared with the nondiapausing individuals) was reduced by about 82%. The alimentary canal, though flaccid, was never empty. Water docs not terminate diapause in the field but rather enhances the emergence of moths from maize stubble after diapause development has been completed.

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