PJS Vol 131 No. 2, December
Page 91-98
0031-7683
The Distribution and Movement of Cotton Bollworm, Helicoverpa armigera Hubner (Lepidoptera: Noctuidae) Larvae on Cotton
Leonardo T. Pascua and Mirriam E. Pascua
Cotton Research Center
Cotton Development Administration, Batac, Ilocos Norte
College of Agriculture and Forestry
Mariano Marcos State University, Batac, Ilocos Norte
The study determined the distribution of various instars of Helicoverpa armigera larvae at different growth stages of cotton under natural infestion and monitored the movement of newly hatched to fifth instar larvae in cotton plants grown in the screen house. The distribution of different instars of H. armigera larvae within the cotton plant was determined weekly from 30 to 93 days after plant emergence (DAE) under natural infestation. Early instar larvae were confined to succulent plant parts like growing tips and small squares. Older larvae were found in big squares and bolls. Most larvae were confined to the upper-third portion from 30 to 37 DAE, to the upper and middle-third portions from 44 to 65 DAE, and to the lower-third portion from 86 to 93 DAE. In the screen house, after introducing newly hatched larvae of H. armigera on terminal buds, squares, flowers and bolls, their movement on the cotton plant was monitored daily until the fifth larval instar in the screen house. First instar larvae of H. armigera remained on those plant parts they were placed on. As the larvae grew older, they moved within or to lower leaf/sympodial branches and eventually to bolls situated at the lower portion of the plant. Larvae placed on terminal buds moved the longest distance followed by those placed on squares, flowers and bolls. The distribution and movement of H. armigera larvae on the cotton plant were governed by the place of oviposition and the developmental stage of the plant.
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