Pest management - Ecological Applications: Toward a Sustainable World - page 162

6.4 Evolution of
resistance and its
management

In the war on pests, it is not unusual for the pest to fi ght back - chemical pesticides
lose their role if the pests evolve resistance (Box 6.1). This problem was often over-
looked in the past, even though the fi rst case of DDT resistance was reported as
early as 1946 (housefl ies, Musca domestica , in Sweden). Now, the scale of the problem
is illustrated in Figure 6.12, which shows the exponential increase in the number
of arthropod invertebrates reported to have evolved resistance and in the number
of pesticides against which resistance has evolved. Two thirds of species are resistant
to more than one pesticide, and the total number of cases of resistance (species

pesticides) is about fi ve times the number of resistant species. Resistance has been
recorded in every family of arthropod pest (including dipterans such as mosquitoes
and house fl ies, as well as beetles, moths, wasps, fl eas, lice and mites) as well as in
weeds and plant pathogens. Take the Alabama leafworm (Section 6.2.6), a moth pest
of cotton, as an example. It has developed resistance in one or more regions of the
world to aldrin, DDT, dieldrin, endrin, lindane and toxaphene.
In the face of evolution of resistance, sustainable pest control depends either on
the continual development of new pesticides that keep at least one step ahead of the
pests or, alternatively, of management strategies that expose the pests to a given
pesticide for only a limited time. I discuss this next.
The evolution of pesticide resistance can be slowed by changing from one pesti-
cide to another, in a repeated sequence that is rapid enough that resistance does not
have time to emerge. River blindness (onchocerciasis) is a devastating disease that
affected millions of Africans. The international community seemed oblivious to its
public health and socioeconomic consequences until the 1970s when a United
Nations mission to West Africa, and a visit by the president of the World Bank,
culminated in the start of a concerted international effort to combat the disease
(Benton et al., 2002). Remarkably, as a result of a blend of pest control and a public
health campaign, the disease was eliminated by early in the twenty fi rst century.
The disease organism, a parasitic worm ( Onchocerca volvulus ), is transmitted by the
biting blackfl y Simulium damnosum , whose larvae live in rivers. By 1999, the blackfl y
larva control program involved 50,000 km of river and an area of 1235,000 km 2 ,

×

Fig. 6.12 Global
increases in the number
of arthropod pest
species reported to have
evolved pesticide
resistance (dotted line)
and in the number of
pesticide compounds
against which resist-
ance has developed
(dashed line). Each
pest, on average, has
evolved resistance to
more than one
pesticide, so there are
now more than 2500
cases of evolution of
resistance (pests ×
compounds) (solid
line). (From Michigan
State University's
Database of Arthropods
Resistant to Pesticides
(http://www.pesticider-
esistance.org/DB/); ©
Patrick Bills, David
Mota-Sanchez & Mark
Whalon.)

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