A severe infestation of the papaya mealybug (Paracoccus
marginatus) nearly wiped out papaya orchards in Pakistan before this largely
farming South Asian country decided to replace conventional chemical pesticides
that were ineffective, with natural predators that proved to be successful.
Developed by agro-biotechnologists and entomologists at the
Pakistani chapter of the UK-based Centre for Agriculture and Bioscience
International (CABI), they introduced the use of Acerophagus papayae, a
parasitoid (insects whose larvae parasite upon and eventually kill the host),
to effectively control the mealybug infestation.
“Farmers are happy with this cost-effective, pesticide-free
technique to deal with the mealybug and now see possibilities of recovering
their papaya farms,” says CABI research coordinator Abdul Rehman.
He regrets though that by the time the biological method
became available many farmers had already shifted to other crops.
Papaya once covered some 921 hectares in the two coastal
provinces of Sindh and Balochistan, according to the National Agriculture
Research Council (NARC)in Islamabad. But, after the first mealybug attack on
papaya was reported in 2008, the area under papaya had shrunk to 307 hectares
by 2014.
Rehman tells SciDev.Net that after the pest had gripped
almost 80 per cent of the papaya orchards, CABI, US Development Agriculture and
the US Agency for International Development initiated the biological control
programme in close collaboration with NARC to stop the pest’s possible spread
to other more important commercial crops.
In 2014, under CABI’s papaya pest management programme, A.
papayae specimens were collected from the coastal areas near the port city of
Karachi, reared in the laboratory and then released into papaya plantations
after screening and environmental assessments.
Field reservoirs of predators
CABI researchers also set up a Natural Enemies Field
Reservoir on the farmers’ fields to breed the A. papayae parasitoid as well as
eight other natural predators of the papaya mealybug.
Amjad Pervez, director-general at the NARC’s Karachi-based
regional office, says that the advantage of the bio-control approach lies in
its simplicity and in the fact that it is self-sustaining.
“Demonstration of the bio-control technique and awareness
building among farmers helped wide-scale adoption and resulted in over 80 per
cent control of the papaya mealybug,” Pervez says. “Besides, the process was
non-laborious, highly affordable and simple enough for farmers not to need
support from government agencies.”
Rehman’s team has hammered out a three-pronged plan to
promote the field reservoirs through public-private partnerships.
“The plan shall be implemented to boost research and
development to strengthen the bio-control process to completely contain papaya
mealybug. Sindh and Balochistan provinces’ farmers’ organisations and vegetable
and fruit traders’ associations will also be engaged in this regard as key
stakeholders,” Pervez explains.
“Controlling the papaya mealybug has helped contain its
potential spread to commercial crops like citrus, tomato, aubergine, peppers,
mulberry, beans and peas, sweet potato, mango, cherry, and pomegranate. Annual
losses, had these crops been affected, would have run into millions of
dollars,” says Pervez.
Rehman says Pakistan’s experience in safely controlling the
mealybug has been shared with CABI chapters in the Asia-Pacific, European, and
African countries.
“Entomologists and fruit pest experts have already
communicated possibilities for replication of the bio-control approach, with
some necessary modifications in countries like Congo, Indonesia, Malaysia,
Nigeria, Sri Lanka, Taiwan and Thailand” he says.
Pesticide resistance
Mealybugs have great resistance to most pesticides. For one
thing they exude waxy secretions that can insulate them against chemicals and
for another they have developed resistance to most commonly used chemical
insecticides, according to a comprehensive Indian study published by Springer
earlier this year.
