Growth and development in a lepidopteran with variable instar number, Pseudocoremia suavis (Geometridae), under standard rearing conditions and when parasitised by Meteorus pulchricornis (Hymenoptera: Braconidae)

Abstract

Growth and development in a lepidopteran with variable instar number,Abstract. Though extra instars are often associated with poor conditions and thought to be a compensation for a low growth rate, the reasons why they are necessary, and for variable instar number existing under standard rearing conditions, are not yet clear. In standard rearing conditions, approximately half of Pseudocoremia suavis larvae had five instars (Type I larvae), and half six instars (Type II larvae). Type II larvae took longer to pupate and reached higher pupal weights than Type I larvae. The extra instar was not related to sexual size dimorphism; Type II larvae were not more likely to be females. Females of both Types pupated later than males and had higher pupal weights; this weight gain was achieved wholly via an extended final instar. Relative growth rates (RGR), instar durations and larval weights on weigh days were otherwise the same for both sexes. For most of the larval period, Type II larvae had lower RGR and lower weights than Type I larvae. They also had shorter 3 rd , 4 th and 5 th instars than Type I larvae, and the estimated weights at each moult were significantly lower. The Types are discussed in terms of being, in species with weight thresholds for pupation, not optional "strategies" involving different critical weight ratios for larval moults, but as an inevitable consequence of physiological timing constraints upon reaching the critical weights for larval moults causing large variation in size after the moult. Small larvae may then need an extra instar to reach pupation. When parasitised in the second instar by Meteorus pulchricornis, P. suavis larvae produced parasitoids in either their fourth (4 th instar emerging (IE)) or fifth instar (5 th IE). The estimated moulting weights at each instar of 4 th IE and 5 th IE hosts were very similar to those of Type I and Type II unparasitised larvae respectively, which, together with similarity of instar duration patterns, is strongly suggestive of Types being present within parasitised larvae. The proportion of 5 th IE hosts in the much slowergrowing parasitised treatment was greater than the proportion of Type II larvae in the unparasitised treatment, as might be expected if Type II is associated with lower RGR. The lack of further Types appearing is consistent with extra instars being a compensation for small weight after the moult rather than low RGR per se.

Variability in development of the striped rice borer, Chilo suppressalis (Lepidoptera: Pyralidae), due to instar number and last instar duration

“…For instance, Barraclough et al . noted that growth in the geometrid moth, Pseudocoremia suavis , fell into two classes depending on instar number (5 or 6) and these classes were independent of sex 14 . In this case, the 6 instar larvae took longer to pupate but had shorter larval durations at the 3–5 instar stage, and changes in instar number likely represented a plastic response to different growth conditions and the need for larvae to reach a particular size for pupation.…”

“…In addition, instar number variation may reflect a genetic polymorphism in cases where variation in instars expressed under constant conditions occurs regardless of sex 12 . Variation in instars may also be unrelated to sex and genetic factors and represent a genetically fixed adaptive strategy; instar variability might serve to produce larvae with a range of emergence times to spread risk associated with emergence under unpredictable unfavorable periods, allowing organisms to hedge their bets 9 13 14 .…”

Biology, morphology and damage of the lesser Coconut weevil, Diocalandra frumenti (Coleoptera: Curculionidae) in southern Vietnam

“…Protein and carbohydrate ratios affected the survival and development of Henosepilachna vigintioctopunctata F. larvae (Coleoptera: Coccinellidae) (Wang et al 2018). Barraclough et al (2014) showed that the increase in the number of Pseudocoremia suavis Butler larvae instars was related to poor nutritional conditions, and more larval instars were needed for pupal emergence. Similar findings on the larvae of Orgyia antiqua (L.) (Lepidoptera: Erebidae) were reported by Esperk and Tammaru (2010).…”

Polyphagous koinobiosis: the biology and biocontrol potential of a braconid endoparasitoid of exophytic caterpillars

“…Most of the host caterpillars are leaffeeding herbivores, but this also successfully parasitizes grain feeders (Ephestia kuehniella Zeller) and wax feeders (Galleria mellonella (L.)) (Lepidoptera: Pyralidae) in the laboratory (Table 1). Whereas a wide range of host instars are acceptable, intermediate instars seem to be the best suited for parasitism (Barraclough et al 2014;Fuester et al 1993;Liu andLi 2006, 2008;Liu et al 2013;Malcicka and Harvey 2014;Zhang et al 2014).…”