CARDI's out to get the moth
Date: Fri 15-Oct-1993
Publication: Weekend Nation
Byline: Ian Gibbs
THE DIAMONDBACK MOTH or to give it its scientific name Plutella xylostella), is
a serious pest of cabbage, cauliflower and broccoli in Barbados.
This tiny insect, whose larvae only reach a length of about 10 millimetres when
fully-grown, can totally destroy every cabbage plant in a farmer's field. One
reason for this is that it can quickly become resistant to regularly-applied
insecticides.
Overuse can also kill the beneficial insects like the tiny parasitic wasps and
predatory beetles. In addition, excessive pesticide application will lead to
unnecessarily high levels of toxic chemical residues in produce and
contamination of the environment.
Against this background, the Caribbean Agriculture Research and Development (CARDI)
Entomology Laboratory in Barbados has been studying ways to control the
diamondback moth.
A survey was conducted on 60 farms throughout the island to gather information
on the agronomy of the crop and the pesticides used for its production.
Following this survey and numerous reports from cabbage growers complaining of
the ineffectiveness of some of the commonly-used, commercially available
insecticides, a series of laboratory tests were conducted to investigate the
problem of insecticide resistance in the diamondback moth.
These tests revealed high levels of resistance to a number of insecticides,
including some of the most often used pyrethroids, organophosphates and
carbamates.
What was even more worriesome, was that a new carbamate, introduced into
Barbados only a year before had already produced resistance levels equivalent to
three times its recommended rate in a diamondback moth population.
The research also focused on the biological control of the diamondback moth by
the tiny parasitic wasps Cotesia plutellae and Tetrastichus sokolowskii which
are well established in Barbados and kill a large number of diamondback moth
larvae.
The effectiveness of these parasites is however, often curtailed by the
indiscriminate used of insecticides which kill both pest and beneficial insects.
Fortunately, there are two insecticides available locally which are not toxic to
the beneficial insects. There are Dipel and Jupiter, both of which are
"biological type" insecticides.
This means greater conservation of the useful insects, no contamination of the
environment, and a substantial reduction in chemical residues on cabbage!
Farmers should still rotate the biological insecticides, as they may also
capable of inducing resistance in the diamondback moth if used exclusively.
CARDI and the Ministry of Agriculture, Food and Fisheries' will continue to test
newer, safer insecticides as they come on the market.
CARDI is attempting to design an Integrated Pest Management programme for this
serious cabbage pest by combining the use of beneficial insects to kill its egg,
larval and pupal stages and the judicious application of safe, non-toxic
biological insecticides. Farmers are already adopting this approach and are
producing excellent crops of wholesome cabbage, cauliflower and broccoli.
We can only hope that this trend will continue.
IAN GIBBS is an entomologist at The Caribbean Research and Development Institute
(CARDI).