Cotton insects are the principal cause of yield losses. Estimates indicate that the yield losses due to insect infections would amount to almost 15% of world annual production. More than 1300 different species of insect pests attack the crop. Among the most common and endogenous species found in cotton fields are:
Egg is greenish blue. The larva of short age is creamy white and black head while large larvae has brownish & blackish spots. Female lays eggs in evening on flowers, flower buds etc of 200 – 400. It can enter into stem, also attack flower buds, balls, enter into it, eat there and secrete fesses outside. The quality of lint is destroyed.
This forms double seed and hibernate there. Female lays 100-250 eggs singly or double gives on flower, flower buds. The larva enter the flower, secrete material which join flower petals and forms rossetted flowers. The infected flower cannot open and it affects the reproductive parts of flower. It also enters the bolls and closes the hole. It destroys lint.
It is most destructive pest. Female lays eggs separately up to 1500. Earlier white then white color. Larvae feed on foliage and fruit. Young larvae feed gregariously and skeletonize leaves.Bigger larvae become solitary and eat large irregular holes in foliage.The damage is found in patches in the beginning, but spread widely if not controlled.
There are two species of Armyworm in Pakistan
Adults are about 1/16 inch in length (1.5 mm), very active, snow-white, and have 4 wings crossed by 2 indistinct gray lines. Nymphs are less than 1/13 inch in length (.2 mm), pointed at both ends, about 1/25(1 mm) inch long, and have 2 pairs of fringed wings.It has winged or wingless adults. One is greenish black other has brown color. Its female lays egg but it also can pathogeneses. Both adult & nymph damage secrete, sugary material on which salty mold grows.
It is yellow green in color and nearly 3 mm long it has alternate host i.e. potato, Brinjal etc. Its population increases in July & August both adult & nymph damage Sucks Chlorophyll and plants are weakened.