ATTRACTION OF COLORADO-POTATO-BEETLE TO HERBIVORE-DAMAGED PLANTS DURING HERBIVORY AND AFTER ITS TERMINATION

Large, undamaged potato plants (> 60 cm, 5-6 weeks old) attract the Co lorado potato beetle (Leptinotarsa decemlineata), but small potato pla nts (15-25 cm high, 2-3 weeks old) do not. However, small plants becom e attractive to CPB when they are damaged. Mechanical damage inflicted with scissors results in short-term (lasting less than 15 min) attrac tion, while more severe damage with carborundum powder results in a lo nger lasting attraction (at least 1 hr). CPB adults are also am-acted to small plants infested with CPB and Spodoptera exigua larvae. After the larvae had been removed for 50 min following a short duration (30 min) of feeding, CPB adults were no longer attracted to the plants. Ho wever, when CPB larvae had been removed after they had fed for 60-90 m in, the plants were somewhat attractive to the beetles, although signi ficantly less than they had been when the larvae were feeding. Attract ion increased with time after feeding ceased. Furthermore, beetles wer e strongly attracted to plants 50 min after larvae were removed when t he plants had been fed upon by larvae for 18-24 hr. Thus It appears th at there are two stages of attraction, first, to volatiles released di rectly from the wound site, and second, to volatiles that are induced in response to herbivory. Chemical analyses of the headspace of infest ed potato plants show that infestation results in the emission of a mi xture of chemicals that is qualitatively quite similar to that emitted by undamaged plants. The major components of the mixture are that emi tted by undamaged plants. The major components of the mixture are terp enoids and fatty acid derivatives such as aldehydes and alcohols. The emission rate of some of these chemicals declines after removal of the beetles, while the emission rate of other chemicals increases with th e duration of beetle feeding and remains at a high level even after re moval of the beetles. Thus, the composition of the mixture changes tem porally during and after herbivore feeding, which may explain the reco rded behavior of the beetles.