Contents - Faperta

Pest Management and the Environment 11
No. of cases
90
80
70
60
50
40
30
20
10
0
Op Carb Spyr
Cotton Cereals Veg/field crops Fruit crops Ornamentals
FIGURE 1.3 Number of insect species that have developed resistance to different insecticides. OP, organophosphates;
Carb, carbamates; and Spyr, synthetic pyrethroids.
other insecticide groups to minimize selection for resistance (Sawicki and Denholm, 1987).
Because of economic advantages and low toxicity to mammals and to some parasites and
predators, much effort has been directed towards developing management strategies aimed
at prolonging the use of synthetic pyrethroids (King and Coleman, 1989). In Australia, the
strategy is dictated by the cotton growing season, which is divided into three stages:
I, early growth; II, the peak squaring, fl owering, and boll formation; and III, end of season.
The use of pyrethroids is restricted to stage II, which corresponds to a 42-day period for a
single H. armigera generation, with no more than three applications. Endosulfan should not
be used during stage III to decrease the chances of reselection for resistance to cyclodiene
insecticides (Forrester, 1990).
The strategy depends for its success in dilution of resistance through interbreeding
with immigrant populations of susceptible insects from unsprayed crops and wild hosts.
However, if resistance is present, and a large proportion of the local over-wintered population
is resistant, then this strategy is unlikely to be effective in the long term. There is some
uncertainty as to whether insecticide resistance confers reduced fi tness in pyrethroid-
resistant strains. Increased incidence of the nerve insensitivity resistance mechanism,
which does not confer the disadvantage of reduced fi tness, implies a major threat to current
resistance management strategies. Counter to the benefi ts derived from diluting
infl uxes of susceptible insects, the capacity of certain insect species for long range movement
has serious implications in relation to the spread of insecticide-resistant populations,
particularly into unsprayed areas or crops (Daly and Gregg, 1985).
The effi cacy of insecticides against target insect pests also depends on the formulation,
type of application equipment, and technology for delivering the insecticides. Some of the
application equipment does not give the desired performance for specifi c crop-pest, climatic,
and topographic conditions. There is a need to devise suitable application equipment to
meet the farmers’ needs in rain-fed agriculture. Further, the types of insecticide formulations
needed in rain-fed areas are different from those for irrigated areas. Dry areas need
different types of pesticide formulations, which require a minimum amount of water.
Hence, research efforts should be concentrated on developing the right type of plant protection
equipment vis-à-vis insecticide formulations. There is a growing support for the