New Horizons in Insect Science Towards Sustainable Pest Management

Integrated Management of Insect-Induced Reddening in Bt Cotton Hybrids 279

boll formation. From the study, it is clear that the
onset of reddening is not harmful if it commences
at late reproductive stage (Dhopte 2001 ).
Pot culture studies involving artificial infesta-
tion with sucking insects confirmed the finding
of insect-induced reddening by cotton leafhop-
per. Other sucking pests such as red spider mites,
whiteflies, aphids and thrips do induce reddening
due to feeding, but results were not consistent.
Infestation of leafhopper on Bt cotton has
been widespread since 2002. Every Bt cotton
seed has been treated with the highly effective

insecticide, imidacloprid. Farmers have also

been spraying the chemical on cotton crops to

control leafhoppers. Recently, leafhoppers were

found to develop resistance to imidacloprid

(neonicotinoid) and development of resistance

to the widely used neonicotinoid insecticides

to control leafhopper incidence is aggravating

the reddening in cotton. Bt cotton is non-toxic

to any of the sucking pests of cotton. Since the

donor parent, Coker 312, is known to be highly

susceptible to sucking pests such as leafhoppers

and thrips, the hybrids showed slightly enhanced

susceptibility to these pests, especially if the

recurrent parent did not possess inherent resis-

tance (Khadi 2007 ).

Yellowing and reddening in leaves were con-

sidered as hopper burn, cupping (an inward curl

of the leaf) and leaf fall, and in severe cases the

vigour of the plant is diminished and it does not

grow, were due to the leafhoppers attack which

starts early in the season. Differential response to

reddening was found among the cultivated com-

mercial Bt cotton hybrids. Among the hybrids

tested, Jackpot, MRC-7347, Marvel and MRC-

7351 were found more tolerant to the manifesta-

tion of reddening symptoms. Bt hybrids such as

RCH 2, RCH 530, Brahma, Arya and Bunny were

found to be highly sensitive to reddening whereas

Fig. 3 Reddening symptoms on various parts of the Bt

cotton. a Leaves, b square, c boll, d bursting boll

Fig. 2 Reddening at different stage of Bt cotton. a Seed-
ling, b vegetative, c boll formation, d boll bursting

Fig. 1 Reddening type in Bt cotton