Mating Disruption with sex pheromone, a novel pest control technology: A need for stewardship for its sustainability in agriculture
It is very
disheartening to read the newspaper report on the 23rd September
2021 that farmers in Bhatinda and Mansa have ploughed back their cotton crops (image)
due to the infestation of pink bollworm. Similar cases of ploughing back the
crop in soil have been reported in the past, as the pest insect has damaged the
crop significantly despite insecticidal use. The pink bollworm has emerged as a
key pest of Bt cotton in the past one decade as it has evolved resistance to
both toxins and found congenial conditions to multiply in cotton ecosystem. The
pest feeds on and bore inside the fruiting bodies, especially bolls that yield
seed and lint (also called seed cotton), the very produce that we call “white
gold” as it fetches cash to the farmers.
Against this
background, the approval in May, 2020 of commercial mating disruption
formulation (PB Rope of Shin-Etsu Chem Co. Ltd., Japan) of sex pheromone
(chemically a mixture in a ratio of 1.11:1.00, respectively of (Z, Z) and (Z,
E) 7,11-hexadecadienyl acetates) holds a great promise for the control of pink
bollworm. It is a historic step in crop protection in India. This method
saturates crop ecosystem with synthetic sex pheromone, which otherwise female
moths would release for attracting males to mate. Male moths lose the tracks of
female moths as they sense trails of sex pheromone everywhere and over the long
period, unable to find female moths and mate with them to produce next
generation. Alternately, male moths also lose their ability to sense pheromone
as their sense organs remain overloaded to be of use again. The female moths
may lay unfertilised eggs, but they do not produce next generation. It is similar to population suppression using insect
(often male) sterile technique, sterility achieved either through irradiation
as in case of screw worm moth control first pioneered by E.F. Knipling and
later in many other insects including pink bollworm or through genetic
transformation using dominant lethal gene technique first pioneered by L. S.
Alphey in early 2010s. The latter technologies do not interfere with mating but
produce eggs as they are either unfertilised or carry lethal genes that cause
their death.
This
significant development of sex pheromone for mating disruption could also be
viewed against the background of their normal use for monitoring pest
incidence. And the pest monitoring has helped to time insecticidal sprays and
other control tactics so that control of pests can be maximised and crop losses
minimised. Occasionally, sex pheromones have been used for mass trapping of
male insects to create male-deficient ecosystem so that female moths remain
un-mated, consequently reducing the next generation.
Reportedly,
mating disruption has been achieved with varying degree of success in pest
insects of forest as well as fruit crops. However, there are limited cases of
successes for pests of annual or season crops worldwide.
India was
one of the few countries to carry out mating disruption studies on pink
bollworm as early as 1980s, after the first commercial formulation based on
hollow fibres was registered in 1978. Over the past four decades, many small as
well as large scale experiments were carried out to test efficacy of various
mating disruption formulations against pink bollworm in cotton. However, need
for this technology was acutely felt as this pest has emerged as a national
pest in 2010s. In 2021, the SABC, New Delhi and Agrovision foundation, Nagpur
in collaboration with PI Industries as well as RASI Seeds Co. are evaluating
this technology for control of pink bollworm in Maharashtra State over a large scale
on the farmers’ fields. Besides, many more field trials are in offing.
It is well
known that mating is a natural need for survival of species. And hence, there
will be ways and means of circumventing the synthetic pheromonal cues by the
male insects to find females for mating. For instance, males of many cotton
bollworm (Helicoverpa armigera) populations respond differently to the
same sex pheromone formulation. In other words, males perceive differences in
sex pheromones as female populations geographically separated secrete
differently. And this agility will help them overcome chemical cues to find
mates. Reports of low catches of male moths vis-à-vis expected zero catches in
the traps or presence of mated female moths give credence to this fact. Furthermore,
cost effectiveness of this technology is very relevant in view of small farms,
need for economy of costs of material and labour, and ability to use area-wide.
Mating disruption formulation technology has improved a lot from the initial
one, hollow fibres first registered in 1978 in USA to Shin-Etsu ropes and even
programmable high emitting aerosol formulations thereby reducing labour costs
of applications, where these matter; and improving release rate in terms of
quantity per unit area per unit time, and also stability under field conditions.
The paste formulations are being developed and may appear to be cheaper, but cost
effectiveness may vary a lot.
As this
method is novel, its sustainability will be of outmost important to all stakeholders. And this will partially
depend upon the answers for some of the following questions
1. Can mass trapping (trapping and
killing male moths) achieve the same results as mating disruption (confusing
male moths so much that mating does not occur and die naturally)?
2. If both achieve the same goal, which
one is more cost effective?
3. Since mass trapping is unregulated,
will its prevalence affect efficacy of mating disruption nearby?
4. Male moths are known to emerge
earlier than female moths in a population of that location to increase chances
of outcrossing, so essential for species survival. What is possibility of
immigrant male moths from different geographic locations in the target area and
interfering with success of mating disruption technology?
5. Will male moths evolve different
receptors or will male moths change perception of pheromonal cues quantitatively?
6. Will female insects emigrate out of
the confines of mating disruption and build up its population elsewhere to be a
cause of concern?
7. As females remain un-mated, will they
evolve over a period of time an ability to produce and release different
pheromonal composition?
8. Are there mated males and females
already in the confines of mating disruption?
9. At what level of pest incidence
should this technology be recommended?
10. At what level of pest incidence or
boll damage, should mating disruption technology be combined with insecticidal
use?
11. As the mating disruption technology is
likely to be costlier, there will be question of minimum area that must be
treated to be effective for pest suppression and also for cost effectiveness,
and what logistics should there be to monitor success of this technology on a regular
basis?
It is of
outmost importance that the Government specifies ideal conditions for use of
this technology to ensure its sustainability.
1. Name of formulation, its active
ingredients (incl isomers) and their proportion
2. Minimum area of cotton crop to be
used to achieve its maximal efficacy.
3. Stability-No of applications or one-time
use formulation during crop season
4. Time of application during crop
season in terms of age of crop
5. Method of application-tieing, paste
application, aerial sprays; and place of application on plants-leaves, bolls,
etc. and spatial distribution in the field esp. guidelines on border rows.
6. Means of monitoring its effectiveness
like use of ‘standard traps’
7. Time frame/age of crop when this
technology be terminated
8. Safety measures to be undertaken
during its use
9. Recommendation for use of
insecticides and/or other control tactics, if moth catches in ‘standard traps’
exceed the set limit
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