13. The effects of intercropping and mixed varieties of predators and parasitoids of cassava whiteflies (hemiptera: aleyrodidae) in Colombia.
Bull. ent. Res., 79, 1989, pp. 115-121
In this paper, the responses of natural enemies of cassava whiteflies to different cropping systems and their role in bringing about reduced whitefly load in cassava intercropped with cowpea are reported.
In this regard, the effects of different cropping systems on the whitefly predator Delphastus pusillus (Le Conte) and on the combined action of the parasitoides Amitus aleurodinus Haldeman and Eretmocerus aleyrodiphaga (Risbec) are discussed.
The predator D. pusillus was low in numbers during the intercrop period and was significantly lower in cassava-cowpea plots than in other treatments for much of the trial. Correlation analysis of predators and prey indicated that the beetles displayed a functional response. D. pusillus was abundant for many months but was unable to control whitefly populations. Ratios of whiteflies to predators coupled with information on prey consumption suggest that predators played only a minor role in whitefly population dynamics. Bettle arrival in the field lagged behind that of the whiteflies, and the highest populations of D. pusillus were in the final month of the trial, reflecting a lack of synchronicity between predator and prey.
D. pusillus attacks a range of whitefly species, but within the systems employed in this study it can be considered a relative specialist because neither cowpea nor maize provided alternative hosts. D. pusillus was never observed on the associated crops, suggesting that they did not provide nectar or pollen to this bettle. However, the presence of cowpea and maize intercrops may have enhanced the activity of this predator. A functional response strongly suggested by beetle distribution in the postintercrop period was not in evidence when intercrops were in the field, and predator: prey ratios were highest in cassava-cowpea systems at this time.
Parasitism of A. socialis was a far more important mortality factor than predation. The role of parasitism in this species was even more important on CMC 40, where predator populations were very low, than on MCOL 2257. Rates of combined parasitism of A. socialis by Amitus aleurodinus and E. aleyrodiphaga were equal between treatments. Overall mortality of the pupal stage was also similar across cropping systems.
Parasitism of T. variabilis was negligible, and for this whitefly D. pusillus was the most important natural enemy.
Intercropping cassava with cowpea reduced populations of the cassava whiteflies Aleurotrachelus socialis and T. variabilis. The effect of the intercrop was residual, with lower populations persisting for six months after cowpea harvest. However, predators were opportunistic, with higher populations correlated with greater numbers of prey in monocultures.
Parasitism levels were independent of cropping system. Therefore, the natural enemies hypothesis can be rejected in explaining the lower populations of whiteflies found on intercropped cassava. Furthermore, the residual effect of the cowpea intercrop on whitefly populations cannot be explained by a build-up of natural enemies in this system during the intercrop period.
A. socialis and T. variabilis larvae suffered substantial mortality in addition to the effects of predators.
Differences in whitefly populations in various cropping systems, including residual effects, cannot be attributed to mortality factors.
In this regard, the effects of different cropping systems on the whitefly predator Delphastus pusillus (Le Conte) and on the combined action of the parasitoids Amitus aleurodinus Haldeman and Eretmocerus aleyrodiphaga (Risbec) are discussed.
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Africa, Nigeria, study, rain forest belt, lowlands, root crops, diseases, integrated pest management, traditional methods, agronomic practices, IITA
ODURO, K.A. et al.
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