Insecticides

 

An insecticide is a pesticide used against insects in all developmental
forms. They include ovicides and larvicides used against the eggs and
larvae of insects, respectively. Insecticides are used in agriculture,
medicine, industry and households. The use of insecticides is believed
to be one of the major factors behind the increase in agricultural
productivity in the twentieth century.
Synthetic insecticides pose some hazards, whereas natural insecticides
offer adequate levels of pest control and pose fewer hazards.
Microbially produced insecticides are especially valuable because their
toxicity to non-target animals and humans is extremely low.
Compared with other commonly used insecticides, they are safe for
both the pesticide users and consumers of treated crops. The action of
microbial insecticides is often specific to a single group or species of
insects, and this specificity means that most microbial insecticides do
not naturally affect beneficial insects (including predators or parasites
of pests) in treated areas.
The spinosyns (A83543 group) are a group of natural products
produced by Saccharopolyspora spinosa that were discovered in 1989.
The researchers isolated spinosyn A and D, as well as 21 minor
analogs. They are active on a wide variety of insect pests, especially
lepidopterans and dipterans, but do not have antibiotic activity.95 The
compounds attack the nervous system of insects by targeting two key
neurotransmitter receptors, with no cross-resistance to other known
insecticides. The spinosyns are a family of macrolides with 21 carbon
atoms, containing four connected rings of carbon atoms at their core
to which two deoxysugars (forosamine and 2,3,4, tri-O-methylrhamnose,
which are required for bioactivity) are attached. Novel
spinosyns have been prepared by biotransformation, using a genetically
engineered strain of Saccharopolyspora erythraea.96 A mixture of
spinosyn A (85%) and D (15%) (spinosad) is being produced through
fermentation and was introduced to the market in 1997 for the control
of chewing insects on a variety of crops. Spinosyn formulations were
recently approved for use on organic crops and for animal health
applications.
Recently, a new naturally occurring series of insect-active compounds
was discovered from a novel soil isolate, Saccharopolyspora
pogona NRRL30141. The culture produced a unique family of
over 30 new spinosyns. They have a butenyl substitution at the 21
position on the spinosyn lactone and are named butenyl-spinosyns
or pogonins.