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Title: Morphology and sexual dimorphism of the weevil Myllocerus undecimpustulatus undatus (Coleoptera: Curculionidae)

Author
item George, Justin
item MORSE, W - Former ARS Employee
item Lapointe, Stephen

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2015
Publication Date: 3/21/2015
Citation: George, J., Morse, W.C., Lapointe, S.L. 2015. Morphology and sexual dimorphism of the weevil Myllocerus undecimpustulatus undatus (Coleoptera: Curculionidae). Annals of the Entomological Society of America. 108(3):325-332.

Interpretive Summary: Myllocerus undecimpustulatus undatus Marshall (Coleoptera: Curculionidae) also known as Sri Lankan weevil, is becoming a major pest of ornamentals and tropical fruit trees in the southern states of USA, especially in Florida. Males and females of this species are not readily distinguishable. Research on the behavior of this weevil would be facilitated if there were a simple way of separating sexes without dissection. Female weevils collected from the field in southeastern Florida were significantly larger than males in length of head, abdomen and overall length. Females weight was approximately twice that of males. The distance between the articulations of the rear legs was significantly higher for females than males; no significant difference was found between the other two pairs of legs. All measures of female elytra were significantly greater than those of male elytra. Females, but not males have a characteristic black-gray marking extending from the ventral mesosternum to the second abdominal segment. Scanning electron microscopic images revealed that females had fewer ovate-to-obovate scales in this region of characteristic black-gray marking, and more plumose (feathery) scales compared with males. Deposition of white cuticular hydrocarbons in this region was less dense on females compared with males. These characters proved sufficient to separate sexes 100% of the time in a blind test and should allow researchers to develop an accurate gestalt to separate males and females of the Sri Lankan weevil.

Technical Abstract: Myllocerus undecimpustulatus undatus Marshall (Coleoptera: Curculionidae) also known as Sri Lankan weevil, is becoming a major pest of ornamentals and tropical fruit trees in the southern states of USA, especially in Florida. Recent findings of this species in Florida citrus groves justify research into their biology and ecology. Identification of semiochemicals involved in their behavioral and chemical communication will help to develop insect control strategies. We studied morphological and sexually dimorphic characters of this species as an aid to rapid separation of sexes for studies aiming to identify semiochemicals that may be of value in management. Female weevils collected from the field in southeastern Florida were significantly larger than males in length of head, abdomen and overall length. Females weight was approximately twice that of males. The distance between the coxal articulations with the metathorax was significantly higher for females than males; no significant difference was found between the prothoracic or mesothoracic coxae. All measures of female elytra were significantly greater than those of male elytra. Females, but not males have a characteristic black-gray marking extending from the ventral mesosternum to the second abdominal segment. Scanning electron microscopic images revealed that females had fewer ovate-to-obovate scales in this region of characteristic black-gray marking, and more plumose scales compared with males. Deposition of white cuticular hydrocarbons in this region was less dense on females compared with males. These characters proved sufficient to separate sexes 100% of the time in a blind test and should allow researchers to develop an accurate gestalt to separate males and females of the Sri Lankan weevil.