Interspecific interactions between Uroplata girardi (Coleoptera: Chrysomelidae) and Ophiomyia camarae (Diptera: Agromyzidae), and their impact on a shared host Lantana camara (Verbenaceae) in South Africa

Abstract

In biological control of weeds, several agent species may be released to attack the target weed with the aim of causing cumulative stress, leading to overall control of the weed. However, this approach may result in competition among phytophagous insects and has been found to contribute to the failure of agents to control the target weed. To test whether competition is the factor limiting biocontrol success of Lantana camara L. (Verbenaceae) in South Africa this study was conducted. Influence of herbivory and interaction by two leaf-mining agents Uroplata girardi Pic (Coleoptera: Chrysomelidae) and Ophiomyia camarae Spencer (Diptera: Agromyzidae) on survival and performance of lantana were investigated using semi-field trials, laboratory experiments and field surveys. Caged lantana under the semi-field conditions were inoculated with U. girardi, O. camarae and with both agents combined to measure impact on its performance and to determine population growth of the biocontrol agents. Female choice for each agent species between infested and uninfested plants was determined in laboratory experiments where caged potted lantana plants were initially inoculated with each species separately, at the later stage the other species and a new plant were introduced to the same cage. To validate the incidence of competition between the agents, five sites in KwaZulu-Natal were surveyed. The impact of U. girardi was greater in the absence of O. camarae whereas their combination appeared to be less their individual effect on lantana. Therefore, there was no synergistic effect between the two agents. Ophiomyia camarae was able to avoid competition by avoiding infested leaves for oviposition while U. girardi laid its eggs indiscriminately and when both utilize the same plant, population growth of the beetle was adversely affected while O. camarae was not. In the field, O. camarae populations increased rapidly from December to May while those of U. girardi were at a minimum during the same period. As a superior competitor, O. camarae reproduces prolifically and is likely to exert substantial herbivore pressure on its host in the field. While, U. girardi population is likely to recover when the fly population declines, it is likely to avoid being displaced completely as previously documented. This study emphasizes the significance of conducting interaction studies on insects, especially those sharing the same niche prior to release. Such studies will avoid the negative impact of competition between agents but will also limit the number of agents used, thus reducing the risk of non-target effects. Copyright