The role of chemicals in the location of host plants by midge pests of UK fruit crops

摘要

Gall midges (Diptera: Cecidomyiidae) are important pests of many horticultural crops. They are difficult to control by conventional means as the larvae develop in galls surrounded by plant tissue. Gravid females need to locate suitable host plant material on which to lay their eggs and there is good evidence that host-produced odour cues are involved. Gall midge pheromones are now available commercially; these attract males to allow monitoring in the field. However there are currently no lures available to attract females. This work aims to develop lures, for up to three gall midge species, which attract gravid females and can be used to monitor females in the field. Three species of gall midges were investigated: the raspberry cane midge, Resseliella theobaldi (Barnes), the blackcurrant leaf midge, Dasineura tetensi (Rübsaamen), and the apple leaf midge, Dasineura mali (Kiefer). Field studies showed gravid raspberry cane midge females are attracted to split canes for oviposition. Chemicals were identified using solid phase microextraction (SPME) which were present only or in much larger quantities after canes split. A lure based on these chemicals was tested in the field with different trap types but no significant attraction was seen to the lures of either male or female raspberry cane midges. Blackcurrant leaf midge females lay their eggs on blackcurrant shoots. A suite of volatiles was identified using SPME which were produced by blackcurrant shoots. Bioassay work was carried out in a four-way olfactometer and a wind tunnel to assess female attraction to shoot material but no attraction was seen in either experiment. Solutions containing natural volatile extracts were obtained using entrainment onto Porapak resin. The effect of these chemicals on female blackcurrant leaf midge antennae was assessed using electroantennography (EAG) but there were not enough responses to conclude that any compound was EAG-active. Apple leaf midges lay their eggs on apple leaf shoots. A suite of chemicals was identified which are produced by apple shoots. EAG runs were carried out on female midges with both natural and synthetic solutions but numbers of responses were low and it was not possible to conclude that any of the compounds were definitively EAG active.