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Abstract Spotted bollworm, Earias vitella (Fab.) (Lepidoptera: Noctuidae) causes huge losses to cotton crop each year. As a relative hardy species among insects, E. vitella tolerates a wide range of environmental conditions and so is prevalent in many regions of the world. To facilitate predictions of its occurrence in the cotton crop, forecasts were using three years of data collected from pheromone traps and accumulated degree days (DD). Moth populations were observed in the second week of August, and in the first and last weeks of September. The DD model predicted that the first, second and third generations of E. vitella produced each year would occur at the accumulation of 2755, 3210 and 3665 Celsius DD respectively. The predicted DD of population peaks matched closely to observe DD results. These observations were consistent in successive generations with a cycle of 263 Celsius DD (predicted) on a yearly average of 241 Celsius DD (observed).
The capture of 8 moths/trap/night accumulated a range of 21 1-2255 DD in the second week of July (equals the minimum ETL), whereas, 11 moths/trap/night accumulated a range of 2288-2370 DD in the third week of July, accurately predicted the start of application of IPM practices to control this pest. These results enable forecasting of seasonal E. vitella population peaks providing additional information vital for development of a successful integrated pest management programme for the spotted bollworm.
Key words: Forecasting, degree days, Earias vitella, population, pheromone traps.
INTRODUCTION Integrated pest management (IPM) is an insect pest control strategy that utilizes a variety of different methods for monitoring insect numbers to identify the optimal time for action to be taken in a bid to prevent the pest populations from increasing beyond the break even pest density. The degree days (DD) forecasting method has been successfully used in the past for forecasting several economic pests, such as Lygus bugs (Sevacherian et al., 1977), codling moth (Johnson, 1988) and the peach tree borer (Johnson, 1989). In the formulation of forecasting models, developmental data from a range of temperatures, help to determine the insect developmental threshold (Herms, 1998). Insect stages are known to have varying developmental thresholds in pink bollworm (Beasley and Adams, 1996), and corn earworm, Heliothis zea (Coop et al., 1993). Threshold and development...