Population assessment of common storage pests in deiri date palm cultivar using spectrophotometric method

Abstract

Opportune and accurate identification of Date pests during storage, is prerequisite for reducing pest damages and having a good export. The present study aimed to define a new sampling method for three main storage pests Oryzaephilus surinamensis (Linnaeus), Ephestia kuehniella (Zeller) and Plodia interpunctella (Hübner) in date Deiri Cultivar, by Spectrophotometer. The experiments were conducted in a completely randomized design with factorial arrangement in two levels. The first factor consisted of 4 levels including different stages in pests life cycle and the second factor had 10 levels including different densities of each development stage of insect species. First, the curve of changes in absorbance level in each life cycle stage was plotted against the wavelength changes and again it was repeated for each species. This curve enabled us to determine the absorption range of the device in different wavelengths. Our results showed that the maximum absorption wavelength for egg, larva, pupa and adult of O. surinamensis, in Deiri Cultivar was 1210, 1230, 1250, 1270 nm, respectively. These values were 1320, 1340, 1380, 1390 nm for E. kuehniella and 1350, 1400, 1410, 1480 nm for P. interpunctella, respectively. The lowest sample size (each sample consisted of 110 g of date fruits) for an accurate estimation of theegg, larva, pupa and adult of O. surinamensis were 1, 2, 2, 2, respectively. These values were 1, 1, 3, 3 samples for E. kuehniella and 1, 2, 2, 2 samples for P. interpunctella, respectively. The Relative Variation values for the four development stages of O. surinamensis were 1.39, 2.41, 2.91 and 3.12, respectively. These values were 1.59, 1.63, 4.62 and 4.34 for E. kuehniella and 1.78. 3.24, 2.62 and 2.24 for P. interpunctella, respectively. The accuracy level of samplings was lower than 10 in all the cases. The Relative net precision values for three studied pests in all life cycle stages were 35.95, 20.73, 17.19, 16.06 for O. surinamensis; 31.32, 30.69, 10.82, 11.53 for E. kuehniella and 28.15, 15.42, 19.05, 22.27 for P. interpunctella, respectively. Therefore, we can conclude that the spectrophotometer can detect the hidden life cycle stages of studied pests in Deiri cultivar during storage and reduce the cost of sampling.