Morphometric Discrimination of Larval Instars and Assessment of Growth Ratio in Eutrichillus comus (Bates) (Coleoptera: Cerambycidae: Lamiinae), a Citrus Branch and Trunk Borer

The coleopteran Eutrichillus comus (Bates) (Cerambycidae: Lamiinae) was recently detected boring into the branches and trunks of Mexican lemon (Citrus aurantiifolia Swingle), Persian lemon (Citrus latifolia Tanaka), and grapefruit (Citrus paradisi Macfad) in the Apatzingán Valley, Michoacán, Mexico. This study characterized the larval development of two E. comus populations by determining the number of instars and estimating their corresponding growth ratios, using larvae collected from Persian lemon and Mexican lemon trees. Morphometric analyses were based on two variables measured: head capsule width and pronotum width. Frequency distributions of each variable analyzed separately did not allow clear delimitation of larval instars in either population. However, frequency distributions based on a proportion factor derived from the product of the two measured variables and the following discriminant analysis clearly indicated that both E. comus populations undergo three distinct instars. The mean growth ratios were 1.50 and 1.36 for the Persian lemon and Mexican lemon populations, respectively. These estimated ratios were not consistent with the growth constant predicted by Dyar’s rule. These findings provide baseline biological information that may contribute to developing preventive management approaches to minimize the risk of this species becoming an economically significant pest.