Investigating the effect of natural enemies and environmental conditions on soil populations of saddle gall midge (PhD)

Abstract

Saddle gall midge Haplodiplosis marginata (Diptera: Cecidomyiidae) is a pest of cereals across Europe. The occasional nature of this pest has resulted in limited and sporadic research activity. There remain important gaps in knowledge due either to a genuine lack of research or to previous research being difficult to access. These knowledge gaps make the development of effective control options difficult. As part of this project, I have reviewed and consolidated the existing literature from research, which spans several decades and encompasses many different countries, so as to identify specific gaps in knowledge that need to be addressed. 

One of the major constraints in effective pest management of this species is a lack of appropriate tools for monitoring. Infestations may go unnoticed until galls are evident in the crop, by which time the damage is done. Furthermore, if chemical controls are to be used, they must be timed to coincide with an appropriate life stage if they are to be effective.

Here, I have demonstrated how the emergence of adult H. marginata can be predicted on a yearly basis using a simple degree-day model and rainfall events. This will allow farmers to forecast the emergence of adults based on weather conditions and initiate inspections of the crop to check for egg-laying. 

This research also provides key insights into the development of this insect in the soil stage which is difficult to observe in the field. In this work, I have also described the development of a pheromone trapping system for H. marginata based on the female sex pheromone. This trap provides a specific, highly effective means of monitoring H. marginata populations and greatly improves upon existing methods of trapping. Lures were optimised through field experiments which tested different lure types, loadings and formulations. Recommendations are provided for use of the trap itself, based on experiments which determined how the position of the trap in the field influenced catch rate.

Additionally, I have developed an assay to identify the presence of H. marginata DNA in the gut contents of arthropod predators. This relied on the development of species-specific primers for use in PCR in order to amplify H. marginata DNA. Using this assay in the field, I have identified seven species of Carabid beetle that naturally predate on H. marginata larvae. 

In all sections of this work, I have addressed the implications of the findings in the context of H. marginata biology and ecology. Furthermore, I have described how this research can be used as the basis for and integrated pest management programme for this pest and proposed avenues for future research.