Contents - Faperta

10 Biotechnological Approaches for Pest Management and Ecological Sustainability
agronomic requirements, and economical. Insecticides are the most reliable means of
reducing crop damage when the pest populations exceed ETLs. When used properly based
on ETLs, insecticides provide a dependable tool to protect the crop from insect pests.
Despite their effectiveness, much insecticide use has been unsound, leading to problems
such as pest resurgence, development of resistance, pesticide residues, nontarget effects,
and direct hazards to human beings (Smith et al., 1974). Despite several advantages of
insecticides for pest control, their use often results in direct toxicity to natural enemies
(Sharma and Adlakha, 1981), and also through the poisoned prey (Sharma and Adlakha,
1986), and a consideration of these is essential for optimizing their use in pest management.
There is substantial literature on the comparative effi cacy of different insecticides
against insect pests. Most insecticide applications are targeted at the larval stages. Control
measures directed at adults, eggs, and neonate larvae are most effective in minimizing
insect damage. Spray decisions based on egg counts could destroy both invading adults
and eggs, and leave a residue to kill future eggs and the neonate larvae. Young larvae are
diffi cult to fi nd, and at times burrow into the plant parts where they become less accessible
to contact insecticides. Ultra low volume (ULV) applicators have been found to be more
effective than the other types of sprayers (Parnell et al., 1999).
Development of Resistance to Insecticides and Strategies for Resistance Management
Excessive and indiscriminate use of insecticides not only has resulted in development of
insecticide-resistant insect populations, but also decimated useful parasites and predators
in the ecosystem. There are several reports that substantiate the development of resistance
to insecticides in insects of public health importance, stored grains, and fi eld crops. A
large number of insects have shown resistance to insecticides belonging to different
groups, and 645 cases of resistance have been documented (Rajmohan, 1998). Most reports
of resistance development pertain to organophosphates (250), followed by synthetic pyrethroids
(156), carbamates (154), and others (including chlorinated hydrocarbons) (85). Many
species (about 85) of insects have developed resistance to more than two groups of insecticides.
The highest numbers of insects and mites showing resistance to pesticides have
been recorded in vegetables (48), followed by those infesting fruit crops (25), cotton (21),
cereals (15), and ornamentals (13). Heliothis/Helicoverpa (which are the most serious pests on
cotton, legumes, vegetables, and cereals) have shown resistance to several groups of insecticides
(Figure 1.3). This has resulted in widespread failure of chemical control, resulting
in extreme levels of debt for farmers, at times even causing them to commit suicide. The
cotton white fl y, Bemisia tabaci (Genn.) has shown resistance to insecticides in cotton, brinjal,
and okra; while the tobacco caterpillar, Spodoptera litura (F.) has been found to be resistant
to insecticides on cotton, caulifl ower, groundnut, and tobacco. Green peach and potato
aphid, Myzus persicae Sulzer, cotton aphid, Aphis gossypii Glover, mustard aphid, Lipaphis
erysimi Kalt., and diamond back moth, Plutella xylostella (L.), have also been found to exhibit
resistance to insecticides in several crops. Development of resistance to insecticides has
necessitated the application of higher dosages of the same pesticide or an increased number
of pesticide applications. The farmers often resort to application of insecticide mixtures
to minimize the insect damage. This has not only increased the cost of pest control,
but also resulted in insecticidal hazards and pollution of the environment. It is in this context
that the use of integrated pest management becomes all the more important.
Insecticide resistance management strategies have aimed either at preventing the
development of resistance or to contain it (Forrester, 1990). All rely on a strict temporal
restriction in the use of certain insecticides such as pyrethroids and their alteration with