29 November 1996

Adjuvants may enhance insecticide selectivity

ADJUVANTS could make broad spectrum insecticides far more selective, according to Portsmouth University research.

Differences in the way chemicals are picked up from sprayed plants by various insects could be exploited, says Martin Ford.

Studies suggest a viscous or sticky additive is the best for trans-ferring insecticides to caterpillars. "We have found we can increase the uptake by caterpillars 15-fold."

Speedy uptake

For beetles, which tend to touch leaf surfaces with only the tips of their legs and then redistribute the pesticide by grooming, speedy uptake is essential. So a low viscosity adjuvant is likely to be best, explains Prof Ford.

"We think it should be possible to devise formulations that could substantially increase the risk to insects as they walk over the leaf. And it might be possible to develop contact-acting treatments that are selective for particular classes of arthropod."

Recent work with seed oil adjuvants highlights the potential. Laboratory experiments adding them to Fastac (alpha-cypermethrin) has allowed the lethal dose for mustard beetles to be cut to one-thousandth of that recommended.

There were some downsides, he admits. It took three times as long to get the same kill. "But it is an interesting direction to follow."

Greases and other semi-solid and solid formulations may have much to offer, he suggests. One in particular is a tablet developed with Cyan-amid. When dissolved and sprayed it leaves a stable polymer mix of active and adjuvant which should withstand wind and rain better than conventional solid treatments.