Ecology of hover flies (Diptera: syrphidae) in relation to trapping methods : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Science with Honours at Lincoln University

Abstract

Habitat manipulation experiments have indicated that hover flies (Diptera: Syrphidae) offer potential as a biocontrol agent of insect pests in New Zealand agricultural systems. However, little knowledge exists of the ecology and phenology of the three species of New Zealand hover fly common in agricultural land. These are Melanostomafasciatum (Macquart), Melangyna novaezelandiae (Macquart), and Eristalis tenax (L.). Similarly, little knowledge exists of the methodological bias inherent in sampling adult hover fly populations using coloured water traps. An understanding of this background information is essential if the potential of hover flies for biocontrol is to be realised. The following experiment was carried out at the Horticultural Research Area, Lincoln University, with the general aim of providing background information on the ecology and phenology of the three species of hover flies found in the agricultural environment, and assessing bias in sampling with coloured water traps. There was a significant inter-specific difference in capture rate between trap types. It is suggested that the use of a single trap type is likely to give an unrepresentative estimate of the populations present. Methods of reducing this bias are discussed. There was a significant difference in pollen 'preference' between species. The possible mechanisms accounting for this difference, and implications for habitat manipulation experiments are discussed. There was good evidence of a new generation of M. fasciatum and M. novaezelandiae in March, and a new generation of E. tenax in May. The sex ratio within M. novaezelandiae and E. tenax varied significantly throughout the trapping period. The mechanisms accounting for variation in species and sex ratio are discussed. The relevance of the results to biocontrol studies is discussed, and suggestions are made for further work.