Abstract
In order to understand the differences of life-history traits between diapause and direct development individuals in the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), the development time, body size, growth rate, and adult longevity were investigated between the two populations, which were induced under 12:12 L:D and 16:8 L:D photoperiods, respectively, at 20, 22, and 25°C. The results indicated that the larval development time, pupal weight, adult weight, and growth rate were significantly different between diapause and direct developing individuals. The diapause developing individuals had a significantly higher pupal and adult weight and a longer larval time compared with direct developing individuals. However, the growth rate in diapause developing individuals was lower than that in the direct developing individuals. Analysis by GLM showed that larval time, pupal and adult weight, and growth rate were significantly influenced by both temperature and developmental pathway. The pupal and adult weights were greater in males than females in both developmental pathways, exhibiting sexual size dimorphism. The dimorphism in adult weight was more pronounced than in pupal weight because female pupae lost more weight at metamorphosis compared to male pupae. Protogyny was observed in both developmental pathways. However, the protogyny phenomenon was more pronounced at lower temperatures in direct developing individuals, whereas it was more pronounced in diapause developing individuals when they experienced higher temperatures in their larval stage and partial pupal period. The adult longevity of diapause developing individuals was significantly longer than that of direct developing individuals. The results reveal that the life-history strategy was different between diapause and direct developing individuals.
Highlights
Body size, development time, and growth rate are three closely-interrelated life-history traits in insects
A short development time is beneficial in nonseasonal environments because it reduces the risk of death before reproduction (Sibly and Calow 1986); a long development time may lead to a larger body size, which is important to fitness (Roff 1992; Stearns 1992)
Growth rate The growth rate was significantly influenced by developmental pathways and temperature, as direct developing individuals had a significantly higher growth rate than diapause ones at all temperatures (Table 2)
Summary
Development time, and growth rate are three closely-interrelated life-history traits in insects. These traits are typical evaluation indicators in fitness and they correlate with other key life-history traits (Nylin and Gotthard 1998). Larger individuals may survive better when there is no food at all, e.g., during hibernation, if body size is correlated with nutrient reserves (Ohgushi 1996). A short development time is beneficial in nonseasonal environments because it reduces the risk of death before reproduction (Sibly and Calow 1986); a long development time may lead to a larger body size, which is important to fitness (Roff 1992; Stearns 1992). In accordance with this, ovipositing females of phytophagous insects typically show a preference for host plants capable of supporting fast larval growth (Thompson 1988; Janz et al 1994)
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