A native to southern parts of the US and
the Caribbean, the insect probably entered India in 1990-91 through imported
chrysanthemum cuttings. “The seed policy adopted in 1988, which liberalised
plant import, made it much easier for such lapses to occur,” says Dr. G.C.
Tiwari, an entomologist with the Indian Council for Agricultural Research (ICAR)
in New Delhi.
The black fly with red eyes was accidentally introduced into
Kenya through chrysanthemum cuttings in the 1970s, and has now reached both
temperate and tropical countries. India offers an ideal hot tropical climate for
the pest.
By the time Dr. Tiwari had alerted agricultural institutes
and the State agriculture departments in 1992 of the havoc the insect could
cause, the pest was beyond control. It had already extensively damaged standing
crops in eight States. Much of the damage was confined to tomato, cotton and
sunflower. According to reports received by the ICAR, the pest had
destroyed an estimated 25% of the tomato crop in Maharashtra, Andhra Pradesh and
Karnataka in the past two years.
Resistant to a large number of pesticides, the fly has the
ability to develop immunity against any chemical within 6-8 generations. It
multiplies at the rate of 15 generations in a year, ruling out use of pesticides
for control. Researchers are studying parasites and other biological methods
that can keep the insect populations under check. “Since it is too late to
eradicate the insect, I think we have no choice but to live with it,” laments
Dr. Tiwari.
The leaf miner was eradicated from glass houses in the UK by
a combination of heavy pesticide treatment, destruction of affected
chrysanthemum plants, steam sterilisation and fumigation by methyl bromide. In
Hawaii and Senegal indigenous parasitoids have been successfully used.
India will have to look for a natural parasite that can be artificially bred and
multiplied.
The fly has the potential to infest 250 crop species in
India. The ICAR has warned that the fly is expected to wreak havoc and can also
cause indirect damage by transmitting other diseases and fungi.
Devinder Sharma is a development
journalist and Director of the Centre for Agriculture and Environment, Noida,
India.
[This article first appeared in Pesticides News No. 25, September 1994, page 14]