| dc.description.abstract | In Kenya, rice is grown in two main areas under irrigation, at Ahera, i~ Nyanza Province near Kisumu and at Mwea-Tebere, in the Eastern Province near Embu town, Entomological, studies, carried out to assess the malaria
vectorial system, in these areas aqd their environs had shown that Anopheles gambiae is the most common vector (Mosha
and Subra, 1982). In order to increase rice yields, the fields are regularly sprayed with a variety of insecticides to control agricultural i~sect pests. The commonly used insecticides are fenitrothio'n (an organophosphate), carbofuran (a carbamate) and also DDT (an organochroline). These s~raying activities could rcsult in cnvironmental contamination pf the larval breeding
sites in the rice pa,ddies of the malaria vector,garobiae,
in which the larvae were found in Lar-ge numbers. Such indirect exposure of mosquitoes to agricultural insecticides may exert a selection pressure that wouid lead to their development of resistance :to insecticides (Chapin and UasS'erstrom 19tH).
Levels of resistance to the insecticides fenitrothion, malathion, carbaryl, DDT and dieldrin in larvae of !~.gambiae collected in the rice fields at Ahero and Mwea were studied
over a one year period, froro October 1986 to September, 1987. Resistance factors of mosquito larvae were n~ar unity for dieldrin and 2-3 times for malathion at both sites and 2 tillles for DDT at Ahero. These lo~ resistance factors indicated little or no resistance to these insecticirles. However, resistance factors to fenitrothion at Ahero of times 30.5, and at Mwea
of times 5.4 and to DDT at Mwea of times 16.5, were high
indicating resistance to these insecticides. This may be explained by the fact that these two insecticides, namely, fenitrothion and DDT, have been regularly used for rice pest control.
Microbial control of !.• ambiae larvae using two bactrial pathogens, Bacillus thuringiensis Berliner variety israelensis .<
de 8arjac (!.l.!.) and Dacillus sphaericus ~eide strain 1593
(~.!:!.) was. also studied both under laboratory and field condi tions with the view to f Lndi ng an aIternati ve control measure in situations when resist~nce to insecticides sets in,
resulting in the inability of insecticides to give the degree of control desired. The following bacterial preparations were tested: IPS82 and flowable formulation Vectobac for !.l.!.and isolate 1593 and a granular formulation ABG6105 for B.s.
comparative bioassays showed tllat younger active larval instars were most susceptible to these bacterial pathogens as determined by both eht spore count compared to international toxic unit system methods for-measuring toxicity of the bacterial isolates. Although the toxic activity of the bacterial formulations was reduced under field condition. it was concluded that this method of control could be an effective alternative for the management of malaria vector mosquitoes in rice irrigation Schemes. | en |
| dc.description.department | a
Department of Psychiatry, University of Nairobi, ; bDepartment of Mental Health, School of Medicine,
Moi University, Eldoret, Kenya | |
