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One aspect of my research focuses on host location and mate recognition strategies of longhorned beetles (Coleoptera: Cerambycidae) attacking hardwood trees. Many cerambycid species colonize woody hosts that are stressed or weakened. Moreover, adult males and females of three species in the subfamily Cerambycinae (Xylotrechus colonus, Megacyllene caryae, and Neoclytus mucronatus mucronatus) are attracted to volatile compounds emanating from weakened hickories, the larval host plant (Ginzel and Hanks, 2005).
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Xylotrechus colonus (M.D. Ginzel)
Rustic borer |
Megacyllene caryae (M.D. Ginzel)
Painted hickory borer |
Neoclytus mucronatus mucronatus
(M.D. Ginzel)
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Males of all three of these species and another, Megacyllene robiniae, also use their elongate and filamentous antennae to recognize mates by contact pheromones present in the cuticular wax layer of females (Ginzel and Hanks, 2003). We have identified the bioactive cuticular hydrocarbons of X. colonus, M. robiniae, and M. caryae (Ginzel et al., 2003a, 2003b, 2006). Recent research on another cerambycid, Neoclytus acuminatus acuminatus, has revealed that males produce pheromones that operate over short or moderate distances (Lacey et al., 2004). Nevertheless, both sexes of N. a. acuminatus also are attracted in the field by volatiles emanating from larval hosts.
It appears that mate location and recognition of longhorned beetles in the subfamily Cerambycinae involves three sequential behavioral stages:
- both sexes are independently attracted to larval hosts by plant volatiles;
- males attract females over shorter distances with pheromones; and
- males recognize females by contact pheromones.
I am also interested in the biosynthesis and endocrine regulation of pheromone production. My postdoctoral research focused on the endocrine regulation of pheromone production in the pinyon Ips bark beetle, Ips confusus, a major pest of pinyon pines in the Southwest.
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Pinyon pine tree (M.D. Ginzel) |
Adult and immature Ips confusus (Forestryimages.org) |
Many bark beetles (Coleoptera: Scolytidae), including I. confusus, produce monoterpenoid aggregation pheromones de novo in midgut tissue via the mevalonate pathway. Populations of these destructive pests may be managed by disrupting pheromone biosynthesis. However, to fully exploit the pheromone-mediated behavior of the beetle, it is important to understand the regulation, expression, and activity of these chemical signals.
Much of our understanding of the endocrine regulation of bark beetle pheromone production comes from the study of Ips pini, the pine engraver. In male I. pini, both feeding and treatment with the noncyclic sesquiterpenoid, juvenile hormone (JH) III, stimulate pheromone production, regulate key enzymes along the mevalonate pathway, and up-regulate transcripts of a number of mevalonate genes. Conversely, we have found that in I.confusus:
- Feeding alone strongly induces the production of ipsenol, a key pheromone component, in males.
- Feeding, but not JH III treatment, stimulates activity of key mevalonate pathway enzymes, including 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-R), only in males.
- However, feeding and JH III both significantly up-regulate mRNA levels of HMG-R and other mevalonate pathway genes.
These data suggest the regulation of pheromone production in Ips is not uniformly controlled by JH III, but rather some other factor, perhaps a peptide hormone, is released from the brain of male I. confusus upon feeding. |
