FILE: <bc-54.htm> Pooled References GENERAL INDEX [Navigate to MAIN MENU ]

SELECTIVE USE OF PESTICIDES

(Contacts)

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.