Applied Entomology and Zoology (1996) 31, 217-223

Tadashi Gomi (1996)
A mechanism for the decrease in developmental period of a trivoltine population of Hyphantria cunea (Lepidoptera: Arctiidae)
Applied Entomology and Zoology 31 (2), 217-223
Abstract: The life cycle of the fall webworm, Hyphantria cunea, has differentiated from bivoltine to trivoltine since the early 1970's in the southwestern areas of Japan. Previous studies showed differentiation in developmental period as well: development was shorter in the trivoltine populations. In the present study, the precise mechanisms of this change were investigated by comparing developmental characteristics between bivoltine (Akita) and trivoltine (Urawa) populations. The theoretical lower threshold temperatures for larval and pupal development were not different between the two populations. The thermal constant for larval development was smaller in the trivoltine population than in the bivoltine population, but that for pupal development was almost identical for the two populations. Most individuals passed six larval instars, and some passed seven in both populations. The incidence of seven-instar larvae was significantly higher in the bivoltine population than in the trivoltinc population. The larval period was significantly longer in the seven-instar type than in the six-instar type. Larvae of the six-instar type grew at similar rates in the two populations. Head width of last instar larvae was larger in the seven-instar type than in the six-instar type, but pupal weight was not statistically different between the two types. These results suggest that the reduction in developmental period in the trivoltine population can be attributed to a reduction in the thermal constant, especially that during the larval stage. A lower incidence of seven-instar larvae appears to be the major mechanism for reducing the thermal constant in the trivoltine population.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Tadashi Gomi

Research topic(s) for pests/diseases/weeds:
general biology - morphology - evolution

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Hyphantria cunea		Japan