Number of larval instars and sex-specific plasticity in the development of the small heath butterfly, Coenonympha pamphilus (Lepidoptera: Nymphalidae)

Abstract

Abstract. The number of larval moults, larval head capsule width and pupal weight were investigated in both direct-developing and diapausing individuals of a South-West European population of Coenonympha pamphilus. The frequency distributions of head widths of successive larval instars overlapped, partly due to variation in the number of larval moults. The larvae that entered diapause went through five instars, instead of the four reported from this species. The evidence indicates that the five instar developmental pathway represents a plastic response rather than an example of compensatory growth. This alternative growth pattern was expressed in response to short photoperiods in parallel with, or as a consequence of, larval diapause. On average, the larvae with five instars had larger heads than their normal siblings. This resulted in comparatively heavier male pupae, while the opposite trend occurred in females. It is concluded that the variation in the number of larval instars is a plastic response to diapause when temperatures remain mild and that it might have an adaptive value in areas with mild winter climates. The sexually dimorphic expression in the larval growth patterns, in terms of pupal weight, may well imply different patterns of allocation of larval resources to adult structures, although sex-dependent differences in investment into purely larval structures cannot be discounted.

Sex Differences in Phenotypic Plasticity Affect Variation in Sexual Size Dimorphism in Insects: From Physiology to Evolution

“…Esperk et al (47) showed that sex differences in the number of instars between males and females are common in insects, and that those species with a sex difference in in-star number exhibit a higher than average level of female-biased SSD. Furthermore, larval instar number can also vary within the sexes, such that plasticity in the number of instars could produce sex differences in plasticity in body size (47, 64). For example, in the grasshopper Chorthippus brunneus , females tend to produce a supernumerary instar when raised on a highquality diet and when raised at high temperature, allowing them to be considerably larger than males (70, 139).…”

Correcting the short‐term effect of food deprivation in a damselfly: mechanisms and costs

“…However, few studies have focused on these sex‐specific correcting mechanisms (e.g. Bian, Wu & Liu 2005; Garcia‐Barros 2006).…”

Occurrence of two different development patterns in Lobesia botrana (Lepidoptera: Tortricidae) larvae during the second generation

“…(i) In the ‘cooler’ areas where second‐generation larvae developed through six instars, pupation was not observed in berries clusters as is typical of nondiapause larvae (Galet, ; Coscollá, ). (ii) The final instar of second‐generation larvae was bigger for larvae developing through six rather than in five instars, as observed in another tortricid (Shaffer & Rock, ), and could be an advantage for winter survival (Fantinou et al , ; García‐Barros, ; Liu et al , ; Pavan et al , ). (iii) In the ‘cooler’ areas where the second‐generation larvae had six instars, the third flight during cold years may be absent (Pavan et al , ).…”