Factors affecting the response ofLongitarsus jacobaeae(Coleoptera: Chrysomelidae) to upwind plant odours

Abstract

AbstractFactors (developmental state, starvation time, host local density and host distance from insects) affecting the response of the ragwort flea beetle,Longitarsus jacobaeae(Waterhouse), to upwind plants of tansy ragwort,Senecio jacobaeae(Compositae), were examined in a wind tunnel. There was seasonal variation in beetle response to host odours. Individuals collected during spring and early summer (6 May to 14 July 1993) showed directed movement toward the upwind plants. However, individuals collected in mid-summer (23 July 1993) showed no significant response to upwind host plants and walked randomly in the wind tunnel. Individuals collected during late summer to autumn (4 August to 23 October 1994) once again showed response to upwind plants, whereas those collected in winter (January 1994) walked randomly in the wind tunnel. The absence of beetle response to plant odours coincided with potential summer aestivation and winter ‘hibernation’. For spring and early summer beetles that responded to plant odours, the strength of the response did not change significantly with the number of plants (1, 2, 4 or 6) presented upwind in the tunnel nor with the starvation time (2, 6, 10, 12, 24 or 36 h) of the tested beetles, and these patterns were consistent for male and female beetles. Individuals responded to plants from a distance of 60 and 300 cm. The speed of movement, similar for males and females, increased slightly asL. jacobaeaeoriented more directly toward host plants.