A laboratory experiment compared development and kikuyu, Pennisetum clandestinum Hochst. ex Chiov. South, consumption in preimaginal grass webworm, Herpetogramma licarsisalis (Walker), at 15, 18, 20, and 25°C. Mean developmental time from oviposition to adult emergence was 25.0 d at 25°C, 43.4 d at 20°C, 50.4 d at 18°C, and 81.4 d at 15°C. Survival decreased with decreasing temperature but not significantly. Total and daily kikuyu leaf area consumed per larva differed significantly with temperature. Leaf consumption increased exponentially with instar. Some larvae developed through six instars, rather than the usually reported five, at temperatures <25°C. Compared with five-instar H. licarsisalis, those with six instars spent longer in the egg stage, had smaller head capsule widths at all but first instar, faster developmental rates but lower kikuyu consumption for each stadium above the second, and slower egg-adult development. Developmental time from egg to adult emergence was significantly shorter for females than for males due to a shorter female pupal stage. Results from this experiment support the view that H. licarsisalis is surviving close to its lower developmental limits over the winter period in Northland, New Zealand, and provide data that will be useful in conjunction with field-collected data for predicting potential geographical distribution and survival.
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