Pest management - Ecological Applications: Toward a Sustainable World - page 163

Table 6.3 History of
pesticide use against
the aquatic larvae of
blackfl ies, the vectors of
river blindness in
Africa. After early
concentration on
temephos and chlor-
phoxim, to which the
insects became
resistant, pesticides
were used on a
rotational basis to
prevent the evolution of
resistance. Note that
the bacterium Bacillus
thuringiensis is a
biological agent
(Section 6.3.4). (After
Davies, 1994.)

Name of pesticide Class of chemical History of use

Temephos Organophosphate 1975 onwards

Chlorphoxim Organophosphate 1980-90

Bacillus thuringiensis Biological pesticide 1980 onwards

Permethrin Pyrethroid 1985 onwards

Carbosulfan Carbamate 1985 onwards

Pyraclofos Organic phosphate 1991 onwards

Phoxim Organophosphate 1991 onwards

Etofenprox Pyrethroid 1994 onwards

covering seven African countries. A massive helicopter pesticide spraying effort
began by using temephos, but resistance in blackfl y populations appeared within 5
years. Temephos was then replaced by another organophosphate, chlorphoxim, but
resistance rapidly evolved to this too (Yaméogo et al., 2001). The strategy of rotating
the use of a range of pesticides, which work in different ways (Table 6.3), has pre-
vented further evolution of resistance, and by 1994 there were few populations that
were still resistant to temephos (Davies, 1994).
Even vertebrates have evolved resistance to some pesticides. A naturally occurring
substance in certain plants, fl uoroacetate, is the basis for the pesticide known as
1080, widely used against vertebrate pests in Australia and New Zealand. Laboratory
testing of rabbit populations soon after 1080 was fi rst introduced, and 25 years later,
revealed a doubling of the dose needed to kill the rabbits (Twigg et al., 2002). This
translated into a reduction from more than a 75% kill rate in a standard pest control
operation where rabbits had not previously been exposed, to as low as 50% where
they had developed resistance. One approach to counter this problem might be to
increase dose rates and the effi ciency of 1080 delivery (on food in bait stations),
because evolution cannot occur if all individuals are killed. However, this would
also increase the likelihood of nontarget mortality. Twigg and his team suggest
instead that, as in the blackfl y case, a range of measures should be used in concert
- including rabbit calicivirus disease (Section 6.1).
Although heritability studies were not performed on the rabbits, it is almost
certain that evolved resistance to 1080 had occurred, as shown defi nitively for Japa-
nese quail ( Coturnix coturnix japonica ) to DDT and for the house mouse ( Mus mus-
culus ) to an anti-blood clotting poison - bromadiolone. The evolution of house
mouse resistance involved genetic selection in a biochemical pathway for a single
enzyme that is less sensitive to the pesticide (Misenheimer et al., 1994).
I have already pointed out some of the pros (and cons) of biological control as
compared to pesticide application. It is worth adding that evolution of resistance to
an introduced natural enemy (whether a predator or parasite) has rarely been docu-
mented. Evolved resistance to a novel pesticide might involve only a single gene. By
contrast, we can expect that 'resistance' to an introduced predator would require
simultaneous changes to a number of the target pest's genes (affecting its behavior,
morphology and/or physiology). Resistance to an internal parasite might be some-
what easier to achieve, and a famous example concerns the introduction to Australia
in the 1950s of the myxoma virus in an early attempt to control rabbits there. Fenner
and Ratcliffe (1965) had the foresight to establish baseline strains of both rabbits