Cotton in Pakistan is mainly damaged by number of lepidopteron caterpillars like spotted bollworms, cotton bollworms, pink bollworms, Army worms etc, and mostly cotton growers have limited expertise to manage these worms due to number of reasons like unable to recognize the entire life cycle of insects, non-existence of reliable pest scouting, limited knowledge of pesticides and beneficial insects etc. Since these worms feed on cotton bolls or flowers, they cause direct and great yield losses. It was presumed that pest management is the weakest area of Pakistani cotton grower. With the Introduction of Bt cotton, the bollworms are no longer an issue; the saving of losses caused by worms and converted into yield gain help to raise farm’ income. Elimination of fear of pink bollworm enabled cotton growers to keep cotton crop for longer in fields. On the other hand, insecticides used for the control of bollworms in cotton substantially reduced and resulted in so called “imbalance” of cotton ecosystem. The imbalanced ecology up graded various potential or minor pests to the status of major pests. Cotton mealybug which was attacking cotton and other crops at very lower incidence converted into a major pest in 2008-09, is a good example of it.
Consequent upon the farmers’ complaints of yellow spots on cotton lint and significantly increasing number of rotten or un-opened bolls, the scientists revealed that two sucking pests are responsible for lint coloration. Based on preliminary studies at Central Cotton Research Institute, Multan it was noted that Red cotton Bug and Dusky Cotton Bug, with cell sap feeding habits (insect with needle like mouth) sucks sap from cotton seed. The insects are preferably feed on seed of partially or unopened bolls. While inserting its needle like mouth into cotton seed for feeding and crawling on bolls, the body secrets colored liquid resulting in lint staining with yellow spots. The discolored lint never appreciated by spinners as its fiber is weakened which end up a low quality yarn or textile product. The saliva also carries bacteria which cause the boll rotten. The bolls aspirated by bugs, if managed to open has lighter seeds making higher seed-lint ratio. The seed produced from such bolls has viability and germination issues hence such crop cannot be used for seed production. Not only this, the hole made for the feeding of insect gets fungus infection and seed cake made from such seed has higher aflotoxine contents. Animals refuse to take such feed and since aflotoxine is extracted in milk if fed to milking animals, the milk processing sector refused to accept milk from the dairies using cotton seed cake as concentrate diet. It is worth mentioning here that aflotoxine is carcinogenic in nature and can cause cancer. Both insects are not new to our environment, rather they were surviving and could not make their existence prominent due to management practices adopted for bollworms or other insects.
Red Cotton Bug, scientifically known as Dysdercus cingulatus, is small insect of about 12-14 mm in length, with deep red legs and antennae. The wings are of two parts outer part is membranous and is black in color, where as inner portion is hard & grayish and has black spot. Females lay eggs in crevasse of moist soil and of bright yellow color. Adult do feed on leaves green bolls and partially opened bolls.
Oxycrenus hyalipennis is the Latin name of Dusky Cotton bug. It is very small insect of about 4-5 mm in length. The body is dusky brown in color, legs are deep brown and wings are faded transparent with black spots. Young ones suck sap from immature seed, which do not ripe and remain light in weight. The adults are picked up with picking of seed cotton and crushed during ginning resulted in stained lint and also produce bad smell.
It is quite important to understand that Bt cotton has nothing to do with these insects, it’s the ecosystem where pesticides for Sundies are withdrawn which facilitated the development and rapid multiplication of these bugs. In non-Bt cotton cultivation pesticides applied for Sundies unnoticeably killed these insects as well, so they never appeared as serious pests. This phenomenon is not new to Pakistan, other countries adopted Bt cotton also had similar experiences with varying degree. Cotton scientists have devised a management strategy for these pests and planned a systematic research during the coming years to address various aspects of these and other potential pests including it biology, natural enemies and study of host range. It is also advised to farmers to report their nearest agriculture officer or research institute/ station if they notice any abnormal behavior of crop, insect or disease symptoms. Strong vigilance may prompt the issue before it could cause an economic loss.
Dr. Khalid Abdullah
Ministry of Textile Industry
Government of Pakistan