Abstract
We have studied the effect of different light gradient regimes on host-plant selection of the carrot psyllid, Trioza apicalis Forster. In both a strong and a weak light gradient, carrot psyllids preferred a carrot leaf placed in higher light intensity. When the choice was between the host (carrot Daucus carota L.) and a non-host (barley Hordeum vulgare L.) virgin adults settled significantly more often on non-host in higher light intensity than on carrot in lower light intensity. In a weak light gradient, none of the gravid females settled on a non-host. In an experiment without light gradient, gravid females showed a preference for carrot, whereas virgin females settled approximately equally on Norway spruce Picea abies Karst. (winter shelter plant) and carrot. Our results show that virgin and gravid individuals have different host-plant selection behaviour, and that they are sensitive to small differences in light intensity. Both factors can create a source of variation in behavioural assays, and should be taken into consideration in future experiments with this and probably also related species. Our results suggest that carrot psyllids can utilize visual cues (light intensity or wavelength) in host-plant selection, and the role of visual cues should be more thoroughly studied.
Highlights
The carrot psyllid (Trioza apicalis Förster) is one of the major pests on carrots (Daucus carota L.) in northern Europe
All virgin females settled on barley, virgin males significantly preferred barley, while there was no significant difference in the number of gravid females settled on carrot or on barley (Fig. 3)
Our results clearly demonstrate the importance of light on the behaviour of carrot psyllids, and that different categories of adults behave differently
Summary
The carrot psyllid (Trioza apicalis Förster) is one of the major pests on carrots (Daucus carota L.) in northern Europe. Over-wintered adults migrate to carrot fields in late May or early June (Láska, 1974; Rygg, 1977; Tiilikkala et al, 1996; Burckhardt & Freuler, 2000) and damage the crop by feeding on the carrot leaves. The average oviposition to adult development time is 52–62.9 days (Láska, 1974; Rygg, 1977) and the new generation usually starts to emerge in mid August. The adults of the new generation migrate 0–5 days after their emergence (Láska, 1974). According to Burckhardt & Freuler (2000) the autumn migration continues until November. Láska (1974) did not observe any autumn migration at temperatures below 11°C
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