Differential Response by Oxyops vitiosa to Variation in Leaf Essential Oil Composition among Melaleuca quinquenervia trees in Florida

F. A. Dray & G. S. Wheeler

(fadray@saa.ars.usda.gov or wheelerg@saa.ars.usda.gov)

Australian researchers have identified two chemical races (i.e. chemotypes) of Melaleuca quinquenervia based upon the terpenoid compounds in the foliage.  Oils of the first type are composed largely (>90%) of trans-nerolidol and little else (Fig. 1a).  In contrast, viridiflorol and/or 1,8-cineole comprise the greatest proportion (40-60%) of oils of the second type (Fig. 1b). We were interested in characterizing populations in Florida, and so collected young leaves from trees at a dozen sites where M. quinquenervia has become naturalized.  We also established an experimental garden of M. quinquenervia grown under identical conditions from seeds collected at these field sites.  Principle components analysis using the terpenoid profiles of the plants shows that both Australian chemotypes are represented in Florida (Fig. 2).  In addition, plants of the viridiflorol/1,8-cineole type segregated into those containing a relatively high amount of terpinenes (a-terpinene, g-terpinene, and terpinene-4-ol) and those lacking these compounds (Fig. 2).  At the population level, a few sites consisted almost exclusively of one chemotype or the other (e.g. sites 3 and 10), but most contained a mixture of the two types (Fig. 3).

             Bioassays in which the biological control agent Oxyops vitiosa was reared on leaves from the two M. quinquenervia chemotypes demonstrated that larval survivorship differs between the two types (Table 1).  Developmental periods differed only for pupae, but insects fed nerolidol-type plants weighed more at all stages than those fed viridiflorol-type plants (Table 2).

Table 1.  Comparison of Oxyops vitiosa survivorship during laboratory bioassays on two chemical races (i.e. chemotypes) of Melaleuca quinquenervia found in Florida.  Chemotype I plants have an abundance of trans-nerolidol, whereas chemotype II plants have an abundance of viridiflorol and/or 1,8-cineole.

Table 2.  Comparison of Oxyops vitiosa development during laboratory bioassays on two chemical races (i.e. chemotypes) of Melaleuca quinquenervia found in Florida.  Chemotype I plants have an abundance of trans-nerolidol, whereas chemotype II plants have an abundance of viridiflorol and/or 1,8-cineole.