Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2004
Publication Date: 12/28/2004
Citation: Dray Jr, F.A., Bennett, B.C., Center, T.D., Wheeler, G.S., Madeira, P.T. 2004. Genetic variation in melaleuca quinquenervia affects the biocontrol agent Oxyops vitiosa. Weed Technology. 18: 1400-1402. Interpretive Summary: Historically, only about one-third of insects released as biological controls for weeds have established persistent populations that have suppressed the target weed in the areas where the insects were introduced. Many hypotheses have been postulated to explain these failures, but one factor that has received relatively little attention is the effect of the weeds' population genetics on the types of insects used in biological control efforts ' insects that will feed, breed, and develop on an extremely restricted suite of host plants. This study combined historical analysis and a technique called isozyme analysis to survey for genetic differences among individuals and populations of the Everglades invader Melaleuca quinquenervia (melaleuca). Insects can't see plant genes, however, so we screened melaleuca in Florida for genetically-based differences in leaf chemistry which the insects can detect. We then assayed an Australian snout beetle (released in Florida as a biological control agent) for evidence that the insect's patterns of growth and development were altered by these differences. The results clearly show that plant genetics can affect biological control insects, and suggest that biological control programs should take plant invasion, population genetics, and leaf chemistry into account when selecting potential biocontrol agents and when deciding where in their native range to collect the insects imported for release.
Technical Abstract: Melaleuca was imported into Florida over a century ago as a landscape plant. A favorable climate and periodic wildfires helped melaleuca thrive; it now occupies about 200,000 hectares in southern Florida. Careful scrutiny of early horticultural catalogs and USDA plant introduction records suggested at least six distinct introduction sources. Allozyme analyses indicated that the pattern of these introductions, and the subsequent redistribution of progeny, have resulted in geographic structuring of the populations in southern Florida. For example, trees on Florida's Gulf Coast have a greater effective number of alleles and exhibited greater heterozygosity than trees on the Atlantic Coast. Essential oil yields from melaleuca leaves followed a similar trend. These differences are partially explained by the predominance of a chemical phenotype (chemotype) very rich in the sesquiterpene (E)-nerolidol in melaleuca trees along the Gulf Coast, but rich in a mixture of the monoterpene 1,8-cineole and the sesquiterpene viridiflorol in trees along the Atlantic Coast. Performance of the melaleuca snout beetle imported as a biological control agent differed dramatically in laboratory studies depending on which chemotype they were fed, with larval survivorship and growth substantially greater on the (E)-nerolidol chemotype. We are currently investigating whether these differences can be detected in the field.