Some effects of temperature and larval food on the development of Spodoptera littoralis (Boisd.) (Lep., Noctuidae)

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Abstract
The development of all stages of Spodoptera littoralis (Boisd.) was studied in controlled-environment cabinets under a range of constant and cycling temperatures. Larvae were tested on three food plants; development was faster on lucerne than on two cultivars of chrysanthemum, Taffeta and Fred Shoesmith. The durations of each instar were similar in relation to larval life span, but at low temperatures and on chrysanthemum many larvae went through an extra instar. Late-instar larvae were nocturnal but larval development was little disturbed by a night-break lighting regime as used in the production of all-the-year-round (AYR) chrysanthemums, and only slightly more so by a reversed temperature cycle. The latter changed the daily pattern of moth emergence which otherwise occurred mostly when temperatures were highest or in the dark. The development results were used to estimate duration of development by summing (a) daily increments of development (100/duration of development), (b) day-degrees (for eggs 28·6 day°C above 14·8°C; for larvae on lucerne 266·1 day°C above 11·5°C, on chrysanthemum 257·1 day°C above 13°C, and above 13°C 177·1 day°C for male pupae and 153·5 day°C for female pupae). The estimates were compared with observed development times for all stages in an environment where temperatures fluctuated naturally. Both methods gave satisfactory estimates when development times were short, but temperature summation was less accurate when maximum temperatures fell close to base temperatures. It is concluded that summation of development increments would give a more consistently accurate account of the life-cycle of S. littoralis on AYR chrysanthemum under glass to enable development to be predicted or past events in the life-cycle to be dated. Tables of development increments against daily maximum and minimum temperatures are given for each stage. To estimate duration of development from these Tables, the daily percentage development corresponding to each day's maximum and minimum temperature is summed up to 100%. This gives an estimate of the median point of hatching or pupation.