Ecological engineering for pest suppression: Promoting parasitoid wasps using nectar plants

Ecological engineering for pest suppression uses cultural practices, usually based on vegetation management, provision of resources such as nectar and pollen to natural enemies promotes biological control, use of trap crops that divert pests away from crops and changing monocultures to polycultures to reduce pest immigration or residency. It provides a methodical, strategic framework and constitutes an attractive option for the design of sustainable agroecosystems globally. More particularly, the Chinese government is attaching great importance to the development of sustainable agriculture. Accordingly, there is a need to improve the scientific underpinnings of ecological engineering for pest control in order to support further development and use.
My literature review has identified important knowledge gaps in ecological engineering for pest suppression. For the use of floral resources to promote parasitoid impact, work is currently dependent upon empirical testing of multiple candidate plants to identify suitable species for each pest―natural enemy interaction in each agroecosystem. This is labour- and time-consuming, and sometimes decisions are made on a weak evidence base. This restricts the promotion and application of ecological engineering for pest suppression in wider ranges of agroecosystems. The present thesis explored a new pathway for nectar plant selection for parasitoid wasps in order to promote parasitoids based on the use of ecological traits data. Unlike earlier analyses focusing on taxonomic categories, I analysed effect sizes in relation to the ecological traits of parasitoids and plants by the available literature. This generated the first set of generalisable guidelines for selecting nectar plants as well as appropriate parasitoid targets for the enhancement of biological control. Within the trait-based guidelines, optimal outcomes resulted when plants with compound umbel or raceme inflorescences and shallow corollas were combined with fecund parasitoids. A constraint of that study was the finding of publication bias in the available literature. A later empirical test, using data I generated from my studies of many parasitoid-plant combinations, gave a data set that was free of publication bias. This showed that the only trait that is significantly positively related to the longevity and fecundity of parasitoid wasps across observations is the plant inflorescence type. Compound umbel is the most positively predictive of parasitoid longevity and fecundity enhancement. An extensive series of field studies extending over four sites and two years confirmed that plant inflorescence type is the most important plant trait for determining the success of ecological engineering for pest suppression. Finally, a major analysis of the volatile organic compounds from various plant species revealed only a weak correlation between flower form and flower VOCs.
Overall, this thesis work has strengthened the foundation for future use of ecological engineering, particularly in relation to understanding the basis for nectar plant-parasitoid interactions. Accordingly, the major contribution of these results to the urgent need for ecological intensification of agriculture is to better guide the selection of optimal nectar plants for use in promoting the ecosystem service of biological control. Whilst the setting of the research has been sub-tropical rice in China, and the implications are much wider-reaching. The guidelines generated by my meta-analysis and supported by my experimental work, open a new methodological approach to guide the sub-discipline of conservation biological control.