Rice Irrigation Scheme Research Articles

Small-scale field evaluation of the monomolecular surface film ‘Arosurf MSF’ against Anopheles arabiensis Patton

A field trial was conducted to test the insecticidal action of the monolayer surface film ‘Arosurf MSF’ applied by knapsack sprayers, against larvae and pupae of Anopheles arabiensis Patton in a rice irrigation scheme in Western Kenya. Larval and pupal densities and the number of emerging adults were determined by dipping and emergence cages respectively. Application of the monolayer by knapsack sprayers provided good coverage. There were high daily mortalities of the fourth instar larvae, with no adult emergence from ‘Arosurf MSF’ treated plots compared to lower fourth instar mortalities and continuous adult emergence from untreated control plots, indicating the potential of the monolayer for control of An. arabiensis mosquitoes in rice fields.

Plasmodium falciparum sporozoite and entomological inoculation rates at the Ahero rice irrigation scheme and the Miwani sugar-belt in western Kenya.

Anopheles arabiensis and An. funestus were collected by pyrethrum spray sheet collections in houses and by human-bait catches at a village in western Kenya adjacent to the Ahero rice irrigation scheme; and using the same methods, An. gambiae s.l. and An. funestus were collected at Miwani, a village in the sugar-cane belt. Plasmodium falciparum sporozoite rates were determined by ELISA. At Ahero the mean sporozoite rates were 1.1% and 4.3% in An. arabiensis and An. funestus, respectively, while at Miwani the rates were 6.0% in An. gambiae s.l. and 4.3% in An. funestus. Entomolgoical inoculation rates (EIR) were derived from both human-bait collections (IR-HBC) and by the proportion of human blood-fed females caught resting indoors (IR-HBF). The IR-HBF appeared to be a more realistic index of EIR. At Ahero and Miwani people were exposed to an average of 416 and 91 infective bites/person/year, respectively. The main vectors were An. funestus at Ahero and An. gambiae s.l. at Miwani. In view of the intense and perennial malaria transmission at Ahero, vector control by insecticides should be considered, while at Miwani, where transmission is seasonal, permethrin-impregnated bed nets could be an alternative to indoor spraying. These measures must be augmented with availability of effective antimalarials.

Mise au point d'un systeme de lutte rationnelle contre les insectes ravageurs sur les perimetres rizicoles irrigues au Burkina Faso

Studies aimed at setting up a system of rational control of pests were carried out at the Vallee du Kou rice irrigation scheme near Bobo-Dioulasso in 1986. The first part of the study focuses on the phytosanitary survey of the above mentioned rice irrigation scheme of 1043 ha through a network of observation sites. This part has given prominence to the fact that the development and importance of the pest infestation were affected by the spacing out of the rice planting and has also allowed us to locate the critical periods of the infestations and their economic incidence. These pests consist mainly of lepidopterous stem borers: Chilo sp., Sesamia sp., and Maliarpha separatella.The second part of the study focused on phytosanitary experiments. Using Decis (Deltamethrin) at 12.5 g a.i. per ha at the intervention thresholds of 5% dead heart and 1% whitehead, has proved to be the most interesting formula as it combines efficiency and profitability.The system of rational control that has been set up based on phytosanitary survey and insecticide application at threshold levels, presents a double advantage, it reduces the number and cost of interventions, and limits the anarchical use of pesticides, hence their harmful effect on the environment. Such experience in insect pest management will be extended to other rice growing areas throughout the country.

Population and cytogenetic observations on Anopheles arabiensis Patton of Mwea Irrigation Scheme, Kenya

A study of the mosquito fauna of the Mwea Rice Irrigation Scheme, Kenya, carried out during 1984 and 1985 identified 13 species, with Anopheles gambiae s. l. comprising 65.71% of the total collection. X-chromosome identification of 652 semi-gravid females resulted in 649 (99.5 %) positive identifications of An. arabiensis , implicating it as the noxious member of the An. gambiae complex present. Inversion polymorphism of chromosomes 2Rb and 3Ra karyotypes was studied in one village population. Seasonal population changes were found to be heavily dependent on rice field surface water. Artificial irrigation for rice farming greatly extended the breeding period per year by linking up the two wet seasons. Adult females fed more frequently on bovids than humans. The mean percentage gonotrophic condition of all females caught in the villagesof Karima, Thiba, Mucii-wa-Urata and Rurumi by pyrethrum spray-sheet collections, miniature light-traps and exit window traps was 69 % bloodfed, 18 % unfed and 13 % gravid. These proportions were statistically shown to be within predictable limits over time and space. The sporozoite infection rate in adult females was 0.55% by manual dissections and 1.2% by the ELISA technique.

Ricefield ecosystem management and its impact on disease vectors

Wetland rice culture and irrigation schemes in tropical and subtropical regions create ecological conditions favourable to the propagation of diseases whose vectors require an aquatic environment. The most important are malaria, schistosomiasis and Japanese encephalitis. This paper reviews (1) the major features of the ricefield as an ecosystem for vectors of selected diseases, (2) the effects of the factors of crop intensification on vectors, and (3) the possible methods of vector control through management of the ecosystem which includes water management, especially the alternate wetting and drying method, conservation of natural enemies, utilization of pesticides of plant origin, and biological control by predators and pathogens.

Struggles over crop rights and labour within contract farming households in a Gambian irrigated rice project

Contract farming schemes based on smallholders are expanding in Africa. Peasant household production is being restructured by the process. Research carried out in the Jahaly Pacharr irrigated rice scheme in The Gambia examines the changes that developed with the genesis of ‘contract farming of the dietary staple, rice. The production routine generated conflicts and struggles within project households over access to and control of female labor. These have led to new labor processes in the project area, which are shaping producers’ abilities to comply with contract farming production strictures.

The Simulation of Small-Holder Rice Irrigation Systems in South-East Asia

A simulation model is presented which incorporates detailed representations of all the major physical components of rice irrigation schemes as commonly found in S.E. Asia. A case study based on the Kaudulla irrigation scheme in Sri Lanka is used to develop and test the model. The paper examines the effects on the scheme water budget of some of the model's main assumptions. These assumptions concern the calculation of lateral and vertical percolatLon losses from the rice fields, and the results show the importance of accurately determining these processes.