The role of genetic diversity in biological control agents

The role of genetic diversity in biological control agents
Sven Tozer and Iain Paterson
Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown, 6140, South Africa

Biological control agents imported into novel environments are often found to be genetically depauperate when compared to the populations in their native ranges. The lack of diversity in the genetic pool may have beneficial or detrimental impacts on aspects of their life histories, host ranges and efficacy as biological control agents. This study examined the effects of reduced genetic diversity in two separate biological control systems, the Pereskia flea beetle, Phenrica guérini Bechyné (Coleoptera: Chrysomelidae), a control agent on Pereskia aculeata Miller (Cactaceae), and Eccritotarsus catarinensis Carvalho (Hemiptera: Miridae) the control agent released on water hyacinth (Eichhornia crassipes (Mart.) Solms-Laub. (Pontederiaceae).

The life history of two genetically distinct strains of P. guerini such, as the duration of development, fecundity,  sex  ratio  of  eclosed  individuals,  weight  at  eclosion  and  weight  at  pupation  were measured. This study found that a more genetically diverse strain performed better than the less diverse strain under uniform conditions. The more diverse strain had an increased developmental time, increased fecundity, was heavier at pupation and eclosion, and expressed a female biased sex ratio with heavier females at eclosion.

Eccritotarsus catarinensis is being investigated in a similar manner to determine if a larger gene pool will increase the efficacy of the control agent. Three genetically distinct strains were created by subjecting  populations  to  varying  degrees  of  bottlenecks.  The  study  will  use  ISSR  markers  to compare the levels of diversity between the treatments. An impact study has been initiated which compares the plants response to inoculation by the different treatments and parameters such as ramet production, biomass production, chlorophyll content and surface area damage will be used to quantify impact and damage. Finally a comparison of the fecundity between the three strains will be conducted. The more genetically diverse strain is expected to perform better than a less diverse strain in terms of fecundity of the insects and impact to the target weed.