The olfactory response of cabbage root fly Delia radicum to the host plant volatile allylisothiocyanate

Abstract

The responses of gravid female cabbage root flies, Delia radicum (L.), to brassica odour and allylisothiocyanate (ANCS) presented in either a discrete plume or uniformly dispersed in air passing through a wind tunnel were investigated. Relatively fast, straight flights occurred in diffuse odour conditions, while in discrete plumes flights were slower with more frequent changes of direction. Flies maintained a constant ground speed and track angle over the straight legs of their flight tracks in two different wind speeds by changing air speed and course. As flies approached an odour source in a discrete plume ground speed was progressively decreased and frequency of turning increased but track angles remained constant. This was achieved by reducing air speed and course angle. Flies released at increasing distances from an odour source moved upwind towards it in a series of short flights, the number relating to distance. The results are discussed in the light of current theories of anemotactic odour source locations and a sequence of orientated behaviour for host plant finding is proposed. Résumé Les réactions olfactives de Delia radicum à l'allylisothiocyanate volatil émis par les plantes‐hôtes L'étude a porté sur les réactions de femelles fécondées de Delia radicum L. à l'odour de chou et à l'allylisothiocyanate (ANCS) offerts, soit sous forme d'un fin panache, soit uniformément répartis dans l'air traversant un tunnel à vent. Avec une odeur diffuse les vols étaient relativement rapides et rectilignes, tandis qu'avec un fin panache les vols étaient plus lents avec des changements de direction plus fréquents. En présence de deux vitesses du courant d'air les mouches ont maintenu leur vitesse au sol et leur angle de vol par rapport à la direction du déplacement constants en modifiant leur vitesse de vol et leur direction. Quand les mouches approchaient de la source odorante dans un fin panache, la vitesse au sol diminuait progressivement et la fréquence des virages augmentait, les angles de vol restant constant. Ceci était obtenu en réduisant de la vitesse de l'air et l'angle du déplacement. Les mouches paraissent utiliser une anémotaxie optomotrice et mécanique pendant la localisation de l'hôte. Les résultats sont discutés à la lumière des théories classiques sur la localisation anémotactique des sources odorantes.

Defence mechanisms of Brassicaceae: implications for plant-insect interactions and potential for integrated pest management. A review

“…Only mated gravid females respond to them (Hawkes and Coaker, 1979;Nottingham and Coaker, 1985;Renwick et al, 1992;Roessingh et al, 1992;Simmonds et al, 1994;De Jong and Städler, 1999;Hurter et al, 1999). In a study examining the role of glucosinolates towards oviposition behaviour of the cabbage root fly using egg counts and electrophysiological recordings from tarsal chemoreceptors, Roessingh et al (1992) showed that the D sensilla on segments 3 and 4 of the tarsus of cabbage root fly females contain a sensitive receptor cell for glucosinolates.…”

“…Gravid females of the cabbage root fly arrive at a hostplant odour source by a series of short upwind flights, landing and reorientating into the wind between flights (Hopkins et al, 1999). The adult female oviposits in the soil close to the stem of Brassica plants (Nottingham and Coaker, 1985;De Jong and Städler, 1999), while damage to the plants is caused by hatched larvae feeding on the roots.…”

Comparison of the egg‐laying behaviour and electrophysiological responses of Delia radicum and Delia floralis to cabbage leaf compounds

“…Both fly species are stimulated by leaf extracts of cauliflower to lay eggs. Previous studies demonstrate that, after stimulation of anemotaxis by crucifer volatiles, D. radicum detects key compounds on the leaf surface of crucifers through sensilla present on the prothoracic tarsi (Finch & Skinner, 1982; Nottingham & Coaker, 1985; Städler & Schöni, 1990; Roessingh et al , 1992; De Jong et al , 2000). The results of the present study confirm that glucosinolates, either in an extract fraction, or as pure synthetic glucobrassicin at 10 −4 M, stimulate the oviposition behaviour of both fly species.…”

Secondary metabolites of the leaf surface affected by sulphur fertilisation and perceived by the cabbage root fly

“…The physical and chemical stimuli that influence the oviposition behaviour of the cabbage root fly have been extensively investigated by different authors (reviewed in Städler 2002). D. radicum oviposition site selection is influenced by the volatile hydrolysis products of GSLs (Wallbank & Wheatley 1979;Ellis et al 1980;Nottingham & Coaker 1985;Tuttle et al 1988), and plant odour plays an additional role in host selection also after landing . The role of other factors, including non-volatile chemicals on the leaf surface (Roessingh et al 1992b;Hurter et al 1999;De Jong et al 2000) as well as leaf colour (Prokopy & Roitberg 2001) have been investigated.…”