Ecological and molecular investigation of wheat bulb fly (Delia coarctata, Fallén, Diptera: Anthomyiidae) for the advancement of population monitoring and control methodologies

Abstract

Wheat bulb fly (WBF) (Delia coarctata, Fallén, Diptera: Anthomyiidae) is a pest of commercial importance in cereal crops. Control is dependent on organophosphates some of which are restricted in the UK, while current oviposition monitoring techniques are labour intensive and subjective. Eggs are not laid in association with a host-plant, therefore, prompt location of a suitable host is critical to the survival of the newly hatched larvae. Wheat bulb fly larvae have been shown to exhibit a positive chemotactic response to wheat and other host-plant seedlings and their root exudates. The objective of this study was to improve the control and population monitoring methodology associated with WBF, by investigating the ecology and specifically the chemical ecology of the WBF. Bioassays were used to investigate the behavioural response of WBF to known chemical constituents of host-plant exudates. Four secondary metabolites were found to be attractive while CO2 was found to alter the behaviour of larvae. Wheat bulb fly oviposition was assessed in field situations to describe egg laying spatially and through time. Geostatistical and ecological techniques were used to observe the spatial dependence and dispersion of oviposition and construct contour maps or scale-sized dot graphs of oviposition density. The traditional single line transect sampling pattern was compared against a more intensive sampling regime. Oviposition monitoring was conducted over a three year period to ascertain the time of peak egg density of this fly. A molecular based diagnostic test to assess WBF egg populations for damage forecasting was developed. A real time polymerase chain reaction (PCR) protocol was produced to estimate field populations of WBF eggs through the quantification of eggs from field samples. In addition endpoint PCR was used to identify the presence or absence of eggs from samples. This study gives the potential to advance current control methodology by providing the basis for the development of a lure and kill or confusion/disruption strategy, while offering a more accurate sampling system and a molecular diagnostic test, for improvement of the management of WBF.