A Novel Damage Intensity Index for Tea Mosquito Bug <i>Helopeltis</i> spp. Infestation in Cocoa

Abstract

The present investigation focused on the development of a new damage intensity index (DII) for the tea mosquito bug Helopeltis spp. (TMB) infestation in cocoa. The new DII was developed based on observable symptoms and the intensity of damage, such as the number and diameter of feeding lesions, and TMB-infested areas on cocoa pods. Statistical techniques, including linear correlation and regression, have been employed to develop an appropriate DII. The study reveals a significant correlation between the mean of total feeding lesions (Xn) and feeding lesions present on the middle portion (Xm) of cocoa pods, surpassing other combinations and indicating a strong relationship between these variables. The damage intensity was estimated using a linear regression approach resulting equation, Xn = 1.79 + 0.25Mn (R2 = 0.989), offers a quantified means of estimating damage intensity on cocoa pods. Analysis of infestation and the regression equation establishes DII values between 1.79 to 76.79. This novel index suggests that the minimum sample size of 90 pods is required for estimating a population with a 95% confidence level to arrive at precision decision making of TMB damage on cocoa pods. The novel damage intensity index and the calculated sample size from this investigation could be useful in conducting various studies, such as germplasm screening, breeding for pest resistance, evaluating the effectiveness of new insecticides, and formulating an IPM package for managing Helopeltis spp. in cocoa.