Cotton Stainer A future threat to Cotton in Pakistan
Organization : MINTEX
It is quite common when a cropping system is shifted to a better system or new crop is introduced; we encounter to a problem: sometime a serious one. Shifting from Desi cotton to American cotton resulted in various sucking and chewing pests, Barani agriculture to irrigated agriculture brought up weed problem, introduction of pesticides resulted in lowering beneficial insects and insecticide resistance issue etc. are some of the good examples. The scientists are equipped to deal with such outbreaks and always keep a keen eye on the changing scenario. Introduction of Bt cotton is a new production system and expected to bring some changes or problems along with its benefits.
Bacillus thuringiensis (abbreviated as Bt) is a soil inhabitant bacterium that produces a toxin which has insecticidal activity. This toxin is only effective against lepidopterist insects or worm or caterpillars or locally known as Sundies. After the discovery of its insecticidal activity, the bacterium was used to kill insects by spraying its solution in early days. Later on, using biotechnology tools, the gene responsible for the production of toxin was isolated and incorporated to cotton, corn, soybean and other crops or vegetables to enable them, through an inbuilt mechanism, to fight against worms or Sundies. Cotton in Pakistan is mainly damaged by number of Sundies like spotted bollworms, American bollworms, pink bollworms, army worms etc, and mostly cotton growers could not overcome these worms due to number of reasons, and end up great yield losses. With the Introduction of Bt cotton, the worms are no longer an issue; substantially increased the yield; raised farm’ income; enabled cotton crop to stay for longer period without fear of pink bollworm. On the other hand, insecticides used for the control of worms in cotton substantially reduced and resulted in so called “imbalance” of cotton ecosystem. This imbalanced ecology resulted in up gradation of various potential or minor pests to the status of major pests. Cotton mealybug is a good example of it.
Consequently upon the farmers’ complaints of yellow spots on cotton lint with significantly increasing number of rotten or un-opened bolls, the scientists revealed that two pests are responsible for lint coloration. Based on preliminary studies at Central Cotton Research Institute, Multan it was told that Red cotton Bug and Dusky Cotton Bug, with cell sap feeding habits (insect their 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 for feeding and crawling on bolls, the body secrets colored liquid resulting in lint staining. 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, also has seed viability issues and significantly reduce yield. The insects are not new to our environment, rather they were present but could not make their existence prominent due to management practices adopted for bollworms and remained in low numbers.
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 and has black spot. Female 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 technical 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 and crushed during ginning resulted in stained lint and 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 that facilitated the outbreak of these bugs. In non-Bt cotton cultivation pesticides applied for Sundies unnoticeably killed these insects as well, so they never appeared as pests. However, the 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. 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