Effect of fertilizer and pesticide on the biocontrol of cereal stemborer's and the awareness of the introduced parasitoid in zanzibar

Abstract

The exotic stemborer, Chilo partellus (Swinhoe) causes the highest economic loss to maize and sorghum yield in the Islands of Zanzibar. A number of studies on its biology, ecology and management in Zanzibar have been conducted since early 1901 (Zanzibar Archive un-published report).However, so much still remains unknown about these pests. As a part of integrated pest management (IPM) strategy for controlling Ch. Partellus in Zanzibar, an exotic Braconidae larval parasitoid, Cotesia flavipes was introduced in 1999 as a classical biological control agent to supplement the indigenous Cotesia sesamiae population after being proved to be successful in Kenya. It was mass released in the coral rag as well as in non-coral areas where maize is grown for both commercial and subsistence. Assessment of the establishment of Cotesia flavipes surveys were conducted during 2004/05. The land quality for agricultural production is better in the Central District than the South and Northeastern zones. The results showed that stemborer density was significantly higher in the North at 2.4 stemborers/plant and lower in the Central District at 1.9/plant, and Chilo partellus was the dominant species. The percentage of bored internodes and tunnel length were higher in the North than in other zones during short and long rainy season. Maize cob and grain yield were higher in short than long rainy season, while cob weight was highest in the North during short rainy season, and it was highest in Central District during long rainy season. Similar results were found for the grain weight. Co. flavipes was recovered in all Districts; the highest parasitism level was recorded in the North District on Chilo partellus. Cob and grain weight observed were higher in plantation zone during short rainy season followed by coral rag and semi coral zones (Table 3.5). There was no significant difference of cob weight during long rainy season between coral, semi-coral and plantation zones, respectively. The survey finding showed the parasitism of larval parasitoids of cereal stemborers by Cotesia sp has increased from 4% in 2001 to 8.74% by 2005. The effect of nitrogen equivalent to 0, 60, 120, and 250kglha and insecticide treatments (Furadan) on population densities and parasitism of lepidopteran stemborers, and maize yields were studied in Zanzibar in 2004/05. Furadan application significantly decreased percent bored internodes and tunnel length during the long rains in both the low and high nitrogen treatments, but the effect was not significant during short rains. Results showed that stemborer density per plant increased with nitrogen application level. The survey results showed that Ch. partellus dominated by 3-fold than Sesamia calamistis and 42 fold with Chilo orichalcociliellus. Parasitism by Co. flavipes increased with an increase in nitrogen level. Percentage of bored internodes per plant caused by stemborer decreased with N levels during short rainy season. Maize yield increased 2 to 8 times from 120kglha. However, protected plots did not have yield increase compared with non-protected plots. The results obtained from interviewing farmers revealed that farmers were not aware of the release of biocontrol parasitoids of cereal stemborers. Therefore, more social education is required to improve awareness. About 40% farmers had a fair knowledge of biological control, 24% had good knowledge, and about 36% had no knowledge about this new biocontrol program.