Preliminary Studies on Cardiocladius Oliff1 (Diptera: Chironomidae) As A Potential Biological Control Agent of Simulium Damnosums.L. (Diptera: Simuliidae) Vectors of Onchocerciasis in West Africa

Abstract

In the course of experiments aimed towards the laboratory colonization of Simulium damnosum sensu lato, egg masses of the flies were collected from the field and reared to adults. However, it was observed that with the samples obtained from Boti Falls (River Pawnpawn), the immature stages of S. damnosum were attacked and fed upon by some larvae belonging to the family Chironomidae (Diptera). The presence of two different species of chironomid was suspected because of the occurrence of two peaks of emergence of adult flies from the rearing systems. The chironomid flies were subsequently identified as Cardiocladius oliffi Freeman, 1956 and Cricolopus kisantuensis Goetghebuer, 1934, by morphological means, but C. oliffi was incriminated as the predator. This is the first report of the genus Cardiocladius in West Africa. C. oliffi was then reared together with S. damnosum to quantify predation. These predators caused high mortality among S. damnosum larvae as a result of disturbances, but the actual predation was on immobile pupae. It was observed that even at a ratio of one C. oliffi to five S. damnosum, the predators cause significant decrease in the number of adultS. damnosum emerging from die systems (treatments) as compared to the control (that had no C. oliffi present). The polymerase chain reaction was used to positively incriminate C. oliffi as the predator of S. damnosum. Three sets of primers namely 16S, ND4 and P1-P2 were used to amplify DNA extracted from the Simulium-fed C. oliffi, but the sizes of the PCR products did not differ appreciably to separate by gel elctrophoresis. Then restriction analysis of the PCR products was carried out which resulted in different DNA band profiles for S. damnosum and C. Oliffi. However, the study also established that the chironomid flies could also develop successfully in the system on a fish food diet only. We have not been able to understand the role of C. kisantuensis, whose egg masses are also attached to the egg masses of S. damnosum.