Role of beetles (Coleoptera: Scolytidae and Nitidulidae) in the spread of Phytophthora palmivora pod rot of cocoa in Papua New Guinea. - (:unkn) unknown
This study was initiated after pod-boring beetles (Coleoptera: Scolytidae and Nitidulidae) were seen to preferentially colonise cocoa pod lesions caused by Phytophthora palmivora. We hypothesised that these beetles, which colonise discarded pod cases and infected pods, are and important and previously unrecognised vector of the black pod pathogen, P. palmivora, in cocoa plantations. Beetles colonise lesions within 24 h of their appearance, and the number of holes increases as the lesion expands. Beetles captured from naturally infected pod lesions carry viable pathogen propagules on their bodies. Frass residues on the surface of infected, colonised pods are rich in viable pathogen propagules. Contact insecticides significantly redice both the number of beetle holes and the number of black pod lesions developing on pods, both in the field and under experimental conditions that exclude all sources of inoculum other than that carried by flying beetles. Beetles are attracted to disease lesions and rapidly generate and disseminate secondary inoculum in epidemics of pod rot, and their role must be included in any integrated disease management strategy.
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This study was initiated after pod-boring beetles (Coleoptera: Scolytidae and Nitidulidae) were seen to preferentially colonise cocoa pod lesions caused by Phytophthora palmivora. We hypothesised that these beetles, which colonise discarded pod cases and infected pods, are and important and previously unrecognised vector of the black pod pathogen, P. palmivora, in cocoa plantations. Beetles colonise lesions within 24 h of their appearance, and the number of holes increases as the lesion expands. Beetles captured from naturally infected pod lesions carry viable pathogen propagules on their bodies. Frass residues on the surface of infected, colonised pods are rich in viable pathogen propagules. Contact insecticides significantly redice both the number of beetle holes and the number of black pod lesions developing on pods, both in the field and under experimental conditions that exclude all sources of inoculum other than that carried by flying beetles. Beetles are attracted to disease lesions and rapidly generate and disseminate secondary inoculum in epidemics of pod rot, and their role must be included in any integrated disease management strategy.
Keywords: Phytophthora.; Plagas.