Selenothrips Rubrocinctus (Giard) and the Floral Biology of Cashew in Tanganyika

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Observations were made of the effect of Selonthrips rubrocinctlls on three-year old cashew trees. Inflorescence counts showed that the attacked trees were producing more flowers than the unattacked but it was later found that yields were lower. The trees flowered from July-December reaching a maximum in mid-September. Ninety per cent of the yield was produced between the middle of September and the beginning of December. Thrip attack brought a loss of 259 lb. per acre of nuts, the infested trees producing 378 lb. per acre and the uninfested 637 lb. per acre. It was found that time of development of the inflorescence was not seriously altered by thrips attack. On the other hand the number of male flowers was drastically reduced although the perfect flowers remained at more or less the same level. This seems to have had an effect on pollination as the set of nuts was reduced from 10.2 per cent of the perfect flowers to 3.8 per cent. The percentage of panicles producing mature nuts was also reduced from 93 per cent to 71 per cent. Although thrips reduce yields in this way they cannot be considered serious pests because of the extremely local nature of their attacks, rarely being found in areas of more than a few trees in extent.
East African Agricultural And Forestry Journal, XXV (No. 4), p. 229-234