Abstract
Summer diapause in Helicoverpa assulta (Hübner), which prolongs the pupal stage, particularly in males, is induced by high temperatures. In the laboratory, 3rd-, 4th-, 6th-instar and prepupal larvae were exposed to high temperatures – 33 and 35 °C with a photoperiod of LD16:8 – until pupation to induce summer diapause. The results showed that the incidence of summer diapause was influenced by temperature, stage exposed, and sex. The higher the temperature, the more often summer diapause was attained. Sixth-instar and prepupal larvae were the sensitive stages for summer diapause induction. H. assulta summer-diapausing pupae needed diapause development to resume development when temperatures became favorable. Furthermore, both body mass and energy storage capacity (lipid and glycogen) were significantly affected by diapause rather than sex, and were significantly higher in summer-diapausing pupae than in non-diapausing pupae. In addition, the body mass loss and respiration rate showed that the rate of metabolism in the summer-diapausing pupae was consistently lower than in non-diapausing pupae, which were significantly affected by diapause and pupal age. We conclude that summer diapause in H. assulta is a true diapause, and H. assulta has evolved mechanisms to accumulate energy storage and to lower its metabolism to adapt to hot summers.
Highlights
Diapause in H. armigera was lacking until Nibouche[14] described a “hot thermal diapause” initiated at 37 °C in a population from Burkina Faso
At 33 °C, the incidence of diapause was significantly different among stages exposed; the highest incidence was attained for females and males when 6th-larvae and 4th-larvae were exposed to high temperature until pupation, respectively (Fig. 2a)
The incidence of diapause among larvae at the 3rd, 4th, and 6th instars when treated at the high temperature (35 °C) was significantly higher than that of prepupal larvae exposed to the high temperature (Fig. 3a)
Summary
Diapause in H. armigera was lacking until Nibouche[14] described a “hot thermal diapause” initiated at 37 °C in a population from Burkina Faso. In China, summer diapause in H. armigera, induced by high temperatures, has been demonstrated[15]. Does H. assulta have the same ability to enter summer diapause?. The adaptive significance of winter diapause in H. assulta is obvious: it allows pupae to survive otherwise lethal winter temperatures[27]. The host-plants of the pest are usually available in summer, and the main environmental factor that is known to induce summer diapause is high temperatures. To avoid hyperthermia and the rapid depletion of energy reserves as a result of such deleterious high temperatures, the oriental tobacco budworm may enter summer diapause. How prepared is it to over hot summer?
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