Diapause induction and termination in Hyphantria cunea (Drury) (Lepidoptera: Arctiinae)

Abstract

The fall webworm, Hyphantria cunea (Drury), enters facultative diapause as a pupa in response to short-day conditions during autumn. Photoperiodic response curves showed that the critical day length for diapause induction was 14 h 30 min, 14 h 25 min and 13 h 30 min at 22, 25 and 28°C, respectively. The photoperiodic responses under non-24 h light-dark cycles demonstrated that night length played an essential role in the determination of diapause. Experiments using a short day length interrupted by a 1-h light pulse exhibited two troughs of diapause inhibition and the effect of diapause inhibition was greater in the early scotophase than in the late scotophase. The diapause-inducing short day lengths of 8, 10 and 12 h evoked greater intensities of diapause than did 13 and 14 h. Diapause can be terminated without exposure to chilling, but chilling at 5°C for 90 and 120 d significantly accelerated diapause development, reduced mortality, and synchronized adult emergence. Additionally, the potential for H. cunea from the temperate region (Qingdao) to emerge and overwinter under field conditions in subtropical regions (Nanchang) of China was evaluated. Pupae that were transferred to Nanchang in early July showed a 60% survival rate and extremely dispersed pupal period (from 12 to 82 days), suggesting that some pupae may undergo summer diapause. Diapausing temperate region pupae that were moved out-of-doors in Nanchang during October showed approximately 20% overwintering survival; moreover, those pupae that overwintered successfully emerged the next spring during a period when their host plants would be available. The results indicate that this moth has the potential to expand its range into subtropical regions of China.

Figure 1. Photoperiodic response curves for the induction of pupal diapause in H. cunea at 22, 25 and 28°C (3 replicates, each of at least 30 individuals/treatment; total n = 147–1341).

Figure 2. Photoperiodic response curves for the induction of diapause in H. cunea under non-24 h light–dark cycles at 28°C.

The length of photophase (top left of each panel) was held constant and the scotophase was changed in each experiment (X-axis). (3 replicates, each of at least 30 individuals/treatment; total n = 32–200 for each point).

Figure 3. Night interruption for the induction of diapause in H. cunea under LD 11∶13 h (A) and LD 13∶11 h (B), 28°C regimes.

The scotophase was systematically scanned by 1-h light pulse. (3 replicates, each of at least 30 individuals/treatment; total n = 37–198 for each point).

Figure 4. Duration of pupal diapause in H. cunea under LD 15∶9 at 28°C, after diapause was induced by different photoperiods at 28°C.

Values followed by different letters are significantly different by the Kruskal-Wallis test and Bonferroni multiple comparisons (χ² = 85.29, d.f. = 4, P = 0.000<0.01). Values in parentheses are numbers of adults emerged from diapausing pupae and survival rate after diapause.

Figure 5. Frequency distribution of adult eclosion in diapausing pupae of H. cunea.

The diapausing pupae were transferred to LD 15∶9 at 25°C after exposure to 5°C and DD for different numbers of days. The hatched bar indicates the period of cold exposure. Values followed by different letters are significantly different by Tukey’s multiple comparisons (P<0.05). Values in parentheses are survival rates after diapause and numbers of adults emerged from diapausing pupae.

Figure 6. Frequency distribution of adult eclosion in pupae of H. cunea under natural conditions in Nanchang.

Pupae were collected in Qingdao city and transferred to Nanchang in early July (n = 187).

Figure 7. Cumulative rate of diapause termination in naturally overwintering pupae of H. cunea in spring of 2012 in Nanchang (n = 196).