EFFECTS OF STARVATION IN THE FIRST INSTAR LARVA ON GROWTH, DEVELOPMENT AND SURVIVAL IN THE RED TURNIP BEETLE, ENTOMOSCELIS AMERICANA (COLEOPTERA: CHRYSOMELIDAE)

Abstract

AbstractEggs of the red turnip beetle, Entomoscelis americana Brown, and seeds of Candle cultivar of Brassica campestris L. and Regent cultivar of B. napus L. (Cruciferae) were exposed to seven constant temperatures (10°–25 °C). At each temperature, egg hatching occurred about 1.0–1.5 days sooner than germination in B. campestris and 1.5–2.25 days sooner than germination in B. napus. Also, germination took place about ½ day sooner in B. campestris than in B. napus. These data indicated that the eggs of E. americana and the seeds of B. campestris and B. napus respond similarly to changes in temperature. Newly-hatched larvae of E. americana were starved for 0–8 days at 15°, 20°, and 25 °C. Starvation-related mortality was not high until they had been starved for more than 2–4 days at 15 °C and 1–2 days at 20° and 25 °C, indicating that the first instar larva has a relatively-limited capability to withstand starvation. Among the survivors, the developmental times for most of the starved larvae were significantly longer than those for the unstarved larvae, but the weights of the adults from starved and unstarved larvae were similar, suggesting that starvation delayed growth and development, but had no apparent adverse or lasting effects on these processes. An evaluation of the egg hatching, germination, and starvation data and of the atmospheric air temperature and soil surface temperature data for the areas where B. campestris and B. napus are grown in Canada suggested that the first instar larva of E. americana normally should not suffer high mortality due to starvation in growers' fields where volunteer seedlings of these two species are the major larval food.