Abstract
Changes in body size in response to environmental factors (especially temperature) is one of the crucial traits studied in connection with insect adaptation to climate change. However, current data on the strength and direction of temperature-size responses in Lepidoptera are inconsistent and the reasons for this are unclear. This study investigates the relationship between the adult size of Aporia crataegi L. (Lepidoptera: Pieridae) and spring weather conditions (temperature and rainfall) at different phases in its outbreak cycle (low population density or high abundance). The forewing area of A. crataegi, a univoltine and irruptive Lepidopteran species, was used as a proxy for overall body size. It was found that temperature in the last month before imago emergence (May) and temperature in the larval growth period following overwintering (April) had differing effects on imago size. The fact that the wing size of both male and female A. crataegi increased following higher temperatures in May corresponds with the converse temperature-size rule and is consistent with the predictions of life history theory for univoltine species. Conversely, while imago size decreased following higher temperatures in April, increased rainfall had a slightly positive effect on imago size. The wings of A. crataegi at the peak of abundance were larger than when sampled during periods of low population density, contradicting available data on changes in the body weight of A. crataegi recorded during outbreaks.
Highlights
Body size in insects is an important adaptive trait that correlates with various indicators of fitness: fecundity, mating success, dispersal ability, etc. (Honek, 1993; Tammaru et al, 2002; Kingsolver & Huey, 2008; Dmitriew, 2011)
Arthropods are recognised as having body size reduction mechanisms in response to increased temperatures that differ between species (Ghosh et al, 2013; Horne et al, 2019)
Irruptive species of forest Lepidoptera as a rule face food scarcity due to the gradual defoliation of host plants during their outbreaks (Isaev et al, 2001; Klemola et al, 2004; Myers & Cory, 2013; Isaev et al, 2017), which may be expected to lead to decreases in growth rate and adult body size (Chown & Nicolson, 2004)
Summary
Body size in insects is an important adaptive trait that correlates with various indicators of fitness: fecundity, mating success, dispersal ability, etc. (Honek, 1993; Tammaru et al, 2002; Kingsolver & Huey, 2008; Dmitriew, 2011). Irruptive species of forest Lepidoptera as a rule face food scarcity due to the gradual defoliation of host plants during their outbreaks (Isaev et al, 2001; Klemola et al, 2004; Myers & Cory, 2013; Isaev et al, 2017), which may be expected to lead to decreases in growth rate and adult body size (Chown & Nicolson, 2004). In other species (autumnal moth Epirrita autumnata Borkhausen, bordered white Bupalus piniarius L. and gypsy moth Lymantria dispar L.) increases in abundance lead to rapid decreases in body size: adults or pupae are smaller in outbreak years and larger during periods of low population density (Carter et al, 1991; Isaev et al, 2001, 2017; Klemola et al, 2004; Myers & Cory, 2013). This study aims to investigate the differences in adult size of a univoltine and irruptive species of Lepidoptera in response to changes in environmental temperature, rainfall and outbreak cycle phases
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