FILE: <bc-54.htm> GENERAL INDEX [Navigate to MAIN MENU ]
|
SELECTIVE USE OF PESTICIDES Selective Pesticides. A. "Selectivity" defines
the capacity of a pesticide to spare natural enemies while destroying their
pest host. B. Two types of selectivity:
1. physical: arises from differential exposure of
pests and natural enemies to a pesticide.
2. physiological: arises from a differential inherent
susceptibility on the part of the pest and its natural enemies to a
pesticide. I. Factors that can determine physical
selectivity. A. Preservation of natural enemy
reservoirs during treatment, either within treated areas or within easy
migrational distances from them.
1. maintain adjoining untreated crop areas or stands of
untreated alternate host plants.
2. recolonizing treated areas with mass-reared natural
enemies.
3. staggering chemical treatments of portions of large
plantings.
4. employing spot or strip treatments of chemicals. B. Timing pesticide treatments to
allow for the differential susceptibility and seasonal occurrence of the
various developmental
stages of natural
enemies.
1. the pupal and prepupal stages of parasitoids are
relatively immune to pesticides.
2. the eggs of many predators are laid in protected spots or
are otherwise inherently unsusceptible.
3. adult parasitoids and predators are generally the most
susceptible stages. C. Physical selectivity may also be
conferred by the feeding habits of various natural enemies.
1. internal parasitoid larvae are protected within their
hosts from contact poisons.
2. adult entomophagous insects vary in susceptibility to
stomach poisons in relation to their propensity to ingest insecticide
contaminated hosts, plant exudates or honeydew. D. Physical selectivity also can be
conferred by manipulating the dosage and persistence of pesticides. II. Physiological
selectivity is conferred by a pesticide that is more toxic to a pest species
than to its natural enemies. But, unfortunately, the reverse is usually true. A. A few pesticides have been
developed that are fairly specific against certain groups or species of
arthropods. B. Physiological selectivity is a
costly achievement. The costs involved in the research and development of
pesticides are
tremendous, well in the range of 20-40 million dollars per
compound. If more of the highly specific pesticides are to be developed
for integrated control, something probably will have to be done
to offset those tremendous developmental costs to industry, for
obviously the marketing potentials of selective and specific
pesticides are much less than those of broad-spectrum compounds. C. To make matters worse for
industry, successful integrated control programs have resulted in smaller
demands for pesticides and
a reduced demand for broad-spectrum compounds. The continuation
of this trend could deter industry from trying to find
additional specific compounds with limited market potentials. |