Comparison of damage characteristic and the chlorosis level development of three cassava varieties from red mulberry spider mite Tetranycus truncatus Ehara.

Abstract

Red mulberry mite, Tetranychus truncatus Ehara is one of the most serious pests of cassava in Thailand. The damage severity is related to cassava varieties. The objective of this study was to compare the damage characteristic and the development of the damage levels from the red mulberry mites on three cassava varieties: Huaybong 60, Kasetsart 50 and Rayong 72. Forty female mites were introduced on a one-month-old cassava, with 10 replications for each variety. The experiment was conducted in a net house, during Mach-May 2017. All mite stages, feeding sites and L1-L5 damage level scores were recorded every 3 days, where L1 = no damage, L2= ≤25% chlorosis, L3=50% chlorosis, L4=75% chlorosis, and L5= 100% chlorosis. From the experiment observation, the mites feed on the underside of the leaves, near the midribs and the lateral veins, then spread to the leaf blades. The female mostly laid eggs at the leaf bases near midrib. The feeding and egg laying behaviors were the same for all cassava varieties. Mite population peak on 9thday in Rayong 72, Huaybong 60 and Kasetsart 50 were 124.63, 98.20 and 57.25 individual/leaf, respectively. The development of the damage level from L1-L3 of Huaybong 60 required the shortest duration of 4 days, while Kasetsart 50 and Rayong 72 required 8 and 5 days. All verity required 9 days to develop from L3 to L4. The development of the damage level from L4-L5 of Rayong 72 required the shortest duration of 22 days, while Huaybong 60 and Kasetsart 50 required 26 and 34 days.