The host selection by adults of two flatheaded rootborers Capnodis tenebrionis L. and C. carbonaria Klug was investigated by examinination of their preference for feeding and oviposition among some of their major host tree taxa. We also studied the resistance to both Capnodis spp. of 10 Prunus rootstocks that were being challenged with the buprestid neonates. The scion selection for feeding and oviposition was related to the cyanide potential in the twig cortex; while potential rootstock resistance was related to the amount of the cyanogenic glycosides in the rootstock cortex. Plum and apricot were preferred by C. tenebrionis and peach was preferred by C. carbonaria. All Prunus rootstocks tested were colonized to some extent by both species. Partial correlation was found between cyanide potential and oviposition for C. carbonaria but not for C. tenebrionis. Nor was significant correlation found between cyanide potential and host preference for feeding by both species. Peach and plum, which displayed the highest level of cyanide potential, were also the preferred by both species for feeding and oviposition. Apple, with the lowest cyanide potential, was the least preferred for both activities. We found an inverse relationship between resistance to Capnodis and level of cyanogenic compounds in the root cortex. Adults of both Capnodis spp. were not deterred by high levels of cyanogenic compounds in the scion twig cortex. Our findings suggest that cyanide potential is not a reliable indicator of the degree of resistance in Prunus spp. rootstocks to Capnodis spp.
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Vol. 96 • No. 2