Pest management - Ecological Applications: Toward a Sustainable World - page 153

1.24

1.18

1.12

1.06

1.00
0.94
0

0.20
0.16
0.12
0.08
0.04

0.04

0.08

0.12

0.16

0

0.20

Fig. 6.6 Results of a mathematical model of pest resurgence. A resurgence ratio greater than 1.0
indicates that resurgence occurs after pesticide application. (R is the ratio of pest density after
application to density in the absence of application). Predator and pest dispersal indexes are the
probabilities that an individual predator or prey, respectively, will disperse into the sprayed fi eld
from an adjacent untreated fi eld. Higher dispersal rates of predators reduce the likelihood of
resurgence, unless the pests also have high dispersal potential. (After Trumper & Holt, 1998.)

30

20

10

0

Fig. 6.7 Consequences of the provision of grassland strips (solid circles) as refuges for carabid
beetles (predators of pest insects) in fi elds of corn. Open circles are results where no refuge strip
was provided (corn occurred where the strip would have been). A soil pesticide (the organo-
phosphate terbufos) was applied at the time of corn planting (except in the refuge and control
strips). Carabid beetles achieved much higher densities in the corn-growing season if grassland
refuges were present. (After Lee et al., 2001.)

treated with a soil insecticide to protect the crop from corn rootworm larvae ( Dia-
brotica spp.). The density of carabid beetles, which are potent natural enemies with
good powers of dispersal, recovers to much higher levels than is the case where no
refuge strips were provided (Figure 6.7).

6.2.7 Widespread
effects of pesticides
on nontarget
organisms, including
people

Sometimes the unintended effects of pesticides have been a whole lot less subtle
than target pest or secondary pest resurgence. We have already bemoaned the fact
that the general use of herbicides, coupled with more intensive farming methods,
has eradicated springtime displays of meadow fl owers in Europe (Section 3.1). These
are now restricted to areas of peasant farming. And when massive doses of dieldrin