Canadian Forest Service Publications

Number of instars and sexual dimorphism of Tetropium fuscum (Coleoptera: Cerambycidae) larvae determined by maximum likelihood. 2012. Flaherty, L.; Regniere, J; Sweeney, J. The Canadian Entomologist 144: 720-726.

Year: 2012

Issued by: Atlantic Forestry Centre

Catalog ID: 34152

Language: English

Availability: PDF (request by e-mail)

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Tetropium fuscum (Fabricius) (Coleoptera: Cerambycidae) is a Palaearctic wood borer that has been established in Atlantic Canada since at least 1990. Neither the number of instars nor methods for determining the instar of field-collected larvae have been documented for this species. Head-capsule width was measured for 949 T. fuscum larvae in order to determine the number of instars in this species, estimate the mean and variance of head-capsule widths associated with each instar, and identify whether head-capsule width is sexually dimorphic. Head-capsule width data were analysed using maximum likelihood analysis of mixture models and the Brooks-Dyer rule. Our results provide strong support for the existence of six larval instars, with sexually dimorphic head-capsule widths in instars five and six. The probability of misclassifying larvae into instar-specific and sex-specific categories ranged from 0.6% to 12.8%, with the highest probabilities occuring when assigning a sex to fifth-instar and sixth-instar larvae.