Oviposition site selection in Cactoblastis cactorum (Lepidoptera): constraints and compromises |
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Authors: | H G Robertson |
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Institution: | (1) Department of Zoology and Entomology, Rhodes University, 6140 Grahamstown, South Africa;(2) Present address: Department of Zoology, University of the Witwatersrand, 1 Jan Smuts Avenue, 2001 Johannesburg, South Africa |
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Abstract: | Summary Oviposition by Cactoblastis cactorum on Opuntia ficus-indica and O. aurantiaca was assessed from the positioning of egg sticks on plants in the field. The number of egg sticks laid on O. ficus-indica plants was affected by: (1) plant size; (2) moth emergence near the plant; (3) cladode condition; and (4) plant conspicuousness. These factors contributed towards the clumping of egg sticks on plants. There was no apparent oviposition preference for one of the two host plant species despite the fact that egg predation was higher and fecundity lower on O. aurantiaca. The selection of a site for oviposition on the host plants was influenced by: (1) cladode condition; (2) height above ground; and (3) shelter from wind during oviposition. Succulent cladodes were the favoured sites for oviposition. The evidence suggests that in C. cactorum, oviposition site selection is largely the net result of a compromise between oviposition behaviour selected for increasing the probability of juvenile survival and oviposition behaviour selected for increasing the probability of laying the full complement of eggs. In addition, environmental and physiological factors such as wind and wing-loading, are thought to place constraints on the range of sites available for oviposition. |
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Keywords: | Cactoblastis Opuntia Oviposition |
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