Intraspecific Variability in Number of Larval Instars in Insects.
From: Institute of Zoology and Hydrobiology, University of Tartu, Vanemuise 46, EE-51014 Tartu, Estonia. tome@ut.ee
Journal of economic entomology
- Publish Date: Jun 2007
- ISSN: 0022-0493
- Volume: 100
- Issue: 3
- Pages: 627-45
- Medium: Print
- Language: English
- Citation (JAMA): Esperk Toomas, Tammaru Toomas, Nylin Sören, et al. Intraspecific Variability in Number of Larval Instars in Insects.. J. Econ. Entomol. Jun 2007;100:627-45
Abstract
The number of larval instars varies widely across insect species. Although instar number is frequently considered to be invariable within species, intraspecific variability in the number of instars is not an exceptional phenomenon. However, the knowledge has remained fragmentary, and there are no recent attempts to synthesize the results of relevant studies. Based on published case studies, we show that intraspecific variability in the number of larval instars is widespread across insect taxa, occurring in most major orders, in both hemimetabolous and holometabolous insects. We give an overview of various factors that have been observed to affect the number of instars. Temperature, photoperiod, food quality and quantity, humidity, rearing density, physical condition, inheritance, and sex are the most common factors influencing the number of instars. We discuss adaptive scenarios that may provide ultimate explanations for the plasticity in instar number. The data available largely support the compensation scenario, according to which instar number increases in adverse conditions when larvae fail to reach a species-specific threshold size for metamorphosis. However, in Orthoptera and Coleoptera, there are some exceptional species in which instar number is higher in favorable conditions. In more specific cases, the adaptive value of the variability in instar number may be in reaching or maintaining the developmental stage adapted to hibernation, producing additional generations in multivoltine species, or increasing the probability of surviving in long-lasting adverse conditions.
Mesh Headings (Keywords): Adaptation, Physiological, Animals, Body Size, Feeding Behavior, Humidity, Insects, Larva, Photoperiod, Population Density, Species Specificity, Temperature
Check for Full Text / PubMed Unique Identifier (PMID): 17598520
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