Pheromone-based Crop Protection: Mating Disruption technology needs many researchable inputs to succeed sustainably

Moths of the pink bollworm in the pheromone trap

Farmers' gathering: pheromone MD formulation, PB knot tied on stem of cotton

larva of the pink bollworm feeding inside the raw cotton boll

It was in mid-1980s and early 1990s that the American bollworm caused havoc to cotton production in the country leading some farmers to commit suicides in the erstwhile state of Andhra Pradesh, Maharashtra and others, as they had taken loans in expectation of bumper yields. Farmers did not believe that this bollworm can be a key pest, reducing their cotton production significantly. The pest insect had developed resistance to most of insecticides used in cotton and thrived well. Insecticide-based control of pests was a big failure, affecting environment and health of all stakeholders. Everyone scrambled for solution. Botanicals like neem, microbials like nucleopolyhedrosis virus, and parasites like Trichogramma chilonis were reported to be alternate to insecticides. The need-based use of insecticides was recommended following monitoring with sex pheromone traps, as these were relatively cheap, effective and easily available. Sex pheromones are volatile chemicals usually released by female moths to attract males for mating and this kind of communication remains predominant over other sense organs in insects. Monitoring of the pest insect with pheromone was extensively done in cotton and other host crops of this bollworm in early 1980s. International Crop Research Institute for semi-arid tropics [ICRISAT], Hyderabad and later the State Agricultural Universities took a lead in developing monitoring techniques as well as recommending them in the management of bollworm. The other tactics like mass trapping and mating disruption [MD] with pheromone did not get due attention like monitoring. Consequently, monitoring recommendations were specific to some locations/regions and to some extent, predictive of impeding pest attack; but did not help much in managing pest with concurrent tactics. The American bollworm remained a key pest with regular outbreaks, until Bt cotton was introduced in 2002. As Bt cotton area spread far and wide, the bollworm disappeared from the cotton fields, as it controlled the American bollworm and others too in the initial years.

Of late, the pink bollworm, Pectinophora gossypiella has unexpectedly become a key pest of Bt cotton. As early as 2008, the insect population of this pest insect from Amreli in Gujarat had shown the field-level resistance to Bt Cry1Ac toxin present in the single-toxin Bt cotton, Bollgard-I. Eventually, the pest insect developed resistance to both toxins, Cry1Ac and Cry2Ab present in two-toxin Bt cotton, Bollgard-II. With congenial ecosystem provided by a large area under Bt cotton over many months of the year and being an internal borer inaccessible to insecticidal sprays, the pink bollworm became a key pest throughout the country reducing seed cotton yields as well as affecting fibre quality. In 2013 and 14, the pink bollworm alone caused loss of about 817 million USD and continues to do so annually even a decade later. This year, the Government of Rajasthan had to pay compensation in millions of INR.

In 2021, the pheromone, gossyplure was registered for MD use by the Government. And since then, this technology is undergoing large-scale demonstrations in the country. MD technology was first tried for the pink bollworm in mid-1980s. But in view of limited interest in the management of this pest, this approach was not pursued.

MD involves use of pheromone on a wide-area in high intensity that male moths fail to mate successfully with the female moths, as they remain in the state of confusion for finding female moths due to permeation of cotton ecosystem with pheromone. Normally, plumes of pheromones come from the sustained release formulation and last for months creating a near stable micro-environment for MD.

Studies carried out by the South Asia Biotechnology Centre, Jodhpur in many locations in the country in the past two years show an encouraging result of this technology. This technology helped in increasing yields by 10-30% in various localities. It reduced need for additional insecticidal sprays and enhanced environmental quality. As a result, pesticide industry has shown interest in developing more formulations for implementing this technology. Although this technology is in nascent stage of implementation, it is also important that it remains sustainable technology for pest management for long time to come.

Need for area-wide approach: MD technology is based upon the permeation of cotton ecosystem with pheromone similar to the natural female moth releases to attract male moths. Therefore, for achieving a stable microenvironment, pheromone release has to be sustained for a long time over the wide area, achieving stability of the sort in its quality and quantity, so that male insects on emergence during cotton reproductive period remain in the state of confusion to find female moths and mate successfully. The technology is recommended for 25 hectares for which 10, 000 knots- are provided by the company. At this rate, 160 knots per acre will be needed. Plants are tied at stem with knot at an interval of one meter in straight line for the borders on all sides. Besides, they are well distributed inside the crop. These are applied at square initiation stage. However, in view of small farm holdings, ten-acre or more cotton area should be explored for this technology. As the area declines, per unit pheromone requirement will increase to maintain microenvironment fully saturated with pheromone over a long period of cotton reproductive phase.

Large scale use of this technology will also depend upon the cost and cooperation amongst small farmers coming together to implement this technology.

So, questions in this regard will be

i.                    How small cotton field is a good enough for the success of MD technology?

ii.                  What environmental factors will influence the sustained release of pheromone from the formulation and maintenance of pheromone permeated microenvironment in the cotton ecosystem?

iii.                How many male moths in the monitoring traps in the treatment area have reached the threshold that determines failure of MD? Is this gradable?

iv.                How to know that catches in the monitoring traps in the treatment are result of a] inadequate and uneven permeation of microenvironment of cotton fields with pheromone, b] tolerance of doses by the existing populations, c] change in perception of relative ratios of pheromone components?

v.                  How to grade the success of MD technology-moth catches in treatment vis-à-vis control area; % of sexually used male moths in the catches; concentration of pheromone in the microenvironment of cotton farm; and yields?

vi.                What are the appropriate controls for MD technology? How many traps should there be per acre in control? How far should control plot be to avoid influence of MD treatment fields?

vii.             Are the formulations for MD likely to be misused for mass trapping by the farmers to save costs and pursue a goal of MD by trapping and killing male moths leaving unfertilized female moths alone in the field? Or Are the farmers likely to bring in more area under MD technology using the same number of knots recommended for 25 hectares? 

viii.           Compatibility with other tactics-Should farmers be advised to go ahead with 1-2 prophylactic sprays for the pink bollworm to keep their incidence under check and increase effectiveness of MD?

ix.                If insecticides are to be recommended, should they be sprayed on the basis of moth catches in pheromone traps? Or moth catches in light traps in the control plots? Or egg-laying incidence or larval counts or rosette flower incidence?

x.                  Do the moth catch in the trap and egg laying/larval incidence pattern coincide, precede or succeed? Can we fit it these results in IPM strategy? 

 

Looking at the challenges of ensuring sustainability of MD technology for the pink bollworm management, I am reminded of and feel humbled by the research article, “Pheromones: As the Glamour and Glitter Fade, the Real Work Begins” by Everett R Mitchell, USDA Scientist at Insect Attractants, Behavior and Basic Biology Research Laboratory at Gainsville, Florida in 1986 in Florida Ent 69, 132-139; when pheromone research had reached at its peak.

 

Thanks to Dr. C.D. Mayee, President and Dr. Bhagirath Choudhary, Founder Director, Mr K.S. Bharadwaj of South Asia Biotechnology Centre for this opportunity to discuss MD and interact with farmers and Staff and Students at RARS, Guntur, KVKs, Hanamkonda and Kurnool for an opportunity during the visit in Nov 16-19, 2023.