Host plant has no effect on the performance and fitness related traits of the biological control agent, Pareuchaetes insulata

Host plant has no effect on the performance and fitness related traits of the biological control agent, Pareuchaetes insulata 
Osariyekemwen Uyi1,2, Martin P. Hill1, Costas Zachariades2,3
1Department of Zoology and Entomology, Rhodes University, P. O. Box 94, Grahamstown 6140, South Africa
2ARC-Plant Protection Research Institute, Private Bag X6006, Hilton 3245, South Africa
3School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209 South Africa

Recent studies have elucidated the morphological and genetic differences between the biotype of Chromolaena odorata invasive in southern Africa and the more widespread chromolaena biotype invasive in Asia and West Africa. Incompatibility of biological control agents with the southern African chromolaena biotype has been suggested as a possible factor responsible for the limited success of the biological control of this weed in South Africa. The first biological control agent to establish on Chromolaena odorata in South Africa, Pareuchaetes insulata, was collected in Florida, USA, on chromolaena plants dissimilar to the southern African chromolaena biotype. Although this insect did establish at one site, out of some 30 sites at which over one million individuals were released, its population level in field generally remains low. In order to understand the reasons behind the poor performance of P. insulata, we hypothesized that P. insulata larvae prefer chromolaena from Florida to the southern African chromolaena biotype, and that larvae reared on Florida chromolaena should have higher fitness and performance than those reared on southern African chromolaena.  To test this, we compared neonate larval preference, larval performance, leaf area consumption, fecundity, survival and several other life history traits on two host plants (Florida and southern African chromolaena) in the laboratory. Our results showed that the neonate larvae of P. insulata preferred Florida chromolaena. With the exception of pupal mass, which was higher for individuals reared on the southern African chromolaena biotype, and longevity, which was greater in individuals reared on Florida chromolaena, host plant did not appear to have an influence on other performance parameters and life history traits such as survival rates, development time, female fecundity, duration of egg laying, egg hatchability and mating success. Consequently host plant did not affect host suitability index (HSI) scores. Host plant did not influence leaf consumption. The significantly higher pupal mass of individuals that were fed on southern African chromolaena, compared to the ones that were fed on Florida chromolaena, did not influence female fecundity and other life history traits. Most importantly, our findings indicate that P. insulata preference for Florida chromolaena plants did not have any obvious negative consequence on the reproductive performance and other fitness related traits of the insect. Therefore, we conclude that biotype incompatibility may not be the reason or factor responsible for the limited success and/or the poor performance of P. insulata in the field.