Environmental impact of tsetse control
What will be the environmental
impact of treating cattle with insecticide?
Treating cattle with insecticides to control tsetse can
have major effects on other species of insect. These effects can be beneficial
or, potentially, harmful.
The beneficial effects include reductions in the numbers of biting flies
such as Stomoxys. This fly can transmit diseases mechanically and
it is also a major nuisance pest of cattle. Treating cattle with insecticide
will not eliminate Stomoxys but there are frequent reports that
their numbers are greatly reduced in tsetse control operations (Leak et
Insecticide treatment of cattle can also affect tick populations. This
is a mixed blessing. On the one hand, ticks can cause serious physical
damage to cattle and thus reducing their numbers will prevent this. On
the other hand, indigenous breeds of cattle can develop a natural immunity
to several tick-borne diseases (anaplasmosis, babesiosis, cowdriosis).
The development of this immunity relies on calves being bitten by infected
ticks; the calves develop relatively mild and transient symptoms of disease
and thereafter they are unaffected by further infection. If, however,
cattle first become infected when they are adults, then the disease can
be very debilitating and potentially fatal. For this reason, we need to
be careful that the mass treatment of cattle with insecticide to control
tsetse does not reduce the numbers of ticks to such an extent that cattle
become vulnerable to tick-borne diseases (Torr
et al., 2002).
...and the ugly.
Treating cattle with insecticides can contaminate the animal's dung and,
as a result, kill large numbers of the beetles and flies associated with
cow dung (Vale & Grant, 2001). These insects play a major role in
the natural incorporation of dung into the soil, a process that is crucial
to the maintenance of soil fertility. Disrupting this process could be
disastrous for farmers. The dung becomes contaminated through the cow
ingesting insecticide as it grooms itself and through insecticide accumulating
around the anus. This contamination is generally most marked with pour-on
formulations of insecticide.
How can we avoid these bad effects?
We can largely stop the insecticidal contamination of dung by treating
just the legs of adult cattle with a dip formulation of insecticide. Fortunately,
most tsetse feed on the legs of older and/or larger cattle whereas many
important vectors of tick-borne diseases feed on the ears, udders, and
perianal regions. Thus by treating just the legs of larger animals we
can avoid the harmful effects of pyrethroids yet still control tsetse.
This is a current area of research and it is not yet clear
whether the selective application strategy will work for all species of
tsetse. Results to date indicate that it is effective for Glossina
pallidipes and we are currently carrying out studies to identify appropriate
strategies for other species of tsetse.
Leak, S.G.A., Mulatu, W., Rowlands, G.J. & D’Ieteran, G.D.M.
(1995) A trial of
cypermethrin ‘pour-on’ insecticide to control Glossina pallidipes,
and G. morsitans submorsitans in south-west Ethiopia. Bulletin of
Entomological Research 85, 241-251.
Torr, S., Eisler, M., Coleman, P., Morton, J. & Machila,
N. (2002). Integrated control of ticks and tsetse: A report for the DFID
Advisory and Support services Commission (Project ZV0151; NRI code V0160).
Vale, G.A. & Grant, I.F. (2001). Modelled impact of
insecticide-contaminated dung on the abundance and distribution of dung
fauna. Bulletin of Entomological Research 92,
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