The effects of temperature and photoperiod on the nymphal development of the semi-aquatic grasshopper Stenacris fissicauda fissicaudafrom a Central Amazonian floodplain (várzea) near Manaus were studied. Newly hatched nymphs were collected in the field from the aquatic macrophyte Paspalum repens(Gramineae-Poaceae), and raised under controlled conditions in environmental chambers (8, 12 and 24 hours of light, 27°C and 27/21°C of temperature) and under natural conditions. This species has 5 nymphal instars in males and six in females under longday conditions in the laboratory, as well as during the period with lower precipitation dry season") under natural conditions. However, an extra instar for males (6th) and females (7th) was observed under short-day conditions in the laboratory. This instar occurred during the period with higher precipitation (rainy season) under natural conditions. Temperature and photoperiod were found to interact in the nymphal development under controlled conditions: 1) The number of instars (especially in females) was principally influenced by the photoperiod; 2) The developmental time of instars (in both sexes) was mainly influenced by temperature. The results are discussed under the aspect that light can act as a controlling factor (ecofactor) on the number of nymphal instars during the development of insects in tropical ecosystems, even when located near the equator, due to seasonal changes in insolation and/or light intensity during the year.
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