Abstract
Effects of temperature, photoperiod, and thermoperiod on growth of the black cutworm, Agrotis ipsilon (Hufnagel), were investigated. No evidence of a periodically regulated larval or pupal diapause was obtained. Using 12:12 (L:D) photoperiods at different constant temperatures, developmental threshold temperatures were estimated for each of the postembryonic developmental stages (first instar to adult). Thermoperiods were shown to stimulate larval growth (weight and head width). Thermoperiods also tended to result in lower developmental threshold temperatures and in shorter stadia than did comparable constant temperature photoperiods. However, the percentage of the total larval developmental period represented by each stadium was found to be independent of both photoperiod and thermoperiod. No evidence was obtained that suggested a differential response to temperatures among successive instars. Results are discussed regarding developmental and seasonal biology of the species.
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