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Nitidulid Beetles as Vectors of Monilinia fructicola in California Stone Fruits. K. G. Tate, Former Research Assistant, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Horticultural Research Centre, Research Division, Ministry of Agriculture and Fisheries, Private Bag, Levin, New Zealand; Joseph M. Ogawa, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 65:977-983. Accepted for publication 31 March 1975. DOI: 10.1094/Phyto-65-977.

Under hot, dry conditions in the Central Valley of California, brown rot development in stone fruits was closely associated with the presence of nitidulid beetles and fruit injury caused by the oriental fruit moth and/or natural splitting of the fruit endocarp. During 1971-73, on decaying stone fruits within orchard trees, Carpophilus freemani predominated in June, July, and August while the populations of C. mutilatus and Haptonchus luteolus were rare until August, but increased and became prevalent in September. Throughout the summer, C. hemipterus was present in trace numbers in the trees. In decaying fruit on the orchard floor, C. mutilatus was less abundant than the other species. Carpophilus mutilatus and H. luteolus were important vectors of Monilinia fructicola in late-maturing peach and nectarine cultivars. They were active visitors of oriental fruit moth exit holes in healthy fruit, were contaminated in nature with viable conidia of M. fructicola, and transmitted the spores to injuries in fungicide-treated or untreated fruit, with resultant development of decay. Although C. freemani and C. hemipterus experimentally transmitted M. fructicola and were contaminated in nature with viable conidia, they were not important vectors since neither actively visited injured healthy fruit in furrow-irrigated orchards. Olfactometer tests showed that C. freemani preferred decaying to healthy fruit odors while the other species preferred the latter. Moisture was an important factor which influenced the attraction of all species to injured fruit. These data establish two species of nitidulid beetles, C. mutilatus and H. luteolus, as effective vectors of M. fructicola in late-maturing stone fruit cultivars with injured fruit and may explain why recommended fungicide applications sometimes fail to control fruit decay in California orchards. Control of brown rot of fruit in the field was obtained by insecticide sprays aimed at reducing oriental fruit moth injuries.

Additional keywords: insect transmission, peaches, Carpophilus spp., Sclerotinia fructicola.