Susceptibility of coastal populations of Caribbean pine to attack by southern pine beetle in Belize

Scolytid beetles in the genus Dendroctonus are among the most ecologically important natural enemies of trees in the genus Pinus. In the neotropics, Caribbean pine (Pinus caribaea var. hondurensis) is host to the southern pine beetle (D. frontalis). Epidemic attacks resulting in mass mortality of trees have been reported in various locations in Central America. In previous work in the Mountain Pine Ridge Forest Reserve (MPR) in Belize, we found significant differences in percentage composition of 4-allylanisole (estragole) in oleoresin of trees in areas with high beetle-induced mortality compared with areas that were relatively free from attack. Furthermore, among individual trees there was a negative relationship between the number of pitch tubes visible on the trees (an indicator of the magnitude of attack) and levels of estragole in the oleoresin, strongly suggesting that this compound plays a role in observed patterns of resistance and susceptibility to beetle attack in this species. In work reported here, we addressed the following question: Do estragole levels in coastal populations, whose conservation status has been described as ‘vulnerable,' suggest increased or decreased susceptibility to beetle attack compared with trees in MPR, where epidemic attack has resulted in >90% mortality? We quantified chemical variation in the oleoresin of trees within and among several coastal and MPR stands. Preliminary analyses revealed that levels of estragole were significantly higher in coastal stands than in MPR stands that suffered high beetle-induced mortality, but were similar to MPR stands that escaped epidemic attack. These results suggest that estragole levels may confer some degree of resistance to epidemic beetle attack in these coastal stands of Caribbean pine.