Environmental Engineering Reference
In-Depth Information
cells and death follows rapidly. Ryania extract-based wettable powders exhibit low mam-
malian toxicity with an acute oral LD 50 of 1200 mg/kg channels in the sarcoplasmic reticu-
lum in rats. This causes calcium ion flow into the cells and death follows rapidly. Ryania
extract-based wettable powders exhibit low mammalian toxicity with an acute oral LD 50
of 1200 mg/kg in rats.
19.8.6 Nicotine
Like pyrethrum and rotenone, nicotine, an alkaloid obtained from the foliage of tobacco
plants ( Nicotiana tabacum ) and related species, has a long history as an insecticide. Nicotine
and two closely related alkaloids, nornicotine and anabasine, are synaptic poisons that
mimic the neurotransmitter acetylcholine. As such, they cause symptoms of poisoning
similar to those seen with organophosphate and carbamate insecticides (Hayes 1982).
Owing to the extreme toxicity of pure nicotine to mammals (rat oral LD 50 is 50 mg/kg)
and its rapid dermal absorption in humans, nicotine has seen declining use, primarily as a
fumigant in greenhouses against soft-bodied pests. However, there remains some interest
in preparing stable nicotine fatty acid soaps, presumably with reduced bioavailability and
toxicity to humans (Casanova et al. 2002).
19.9 Microbial Metabolites
Living organisms generally produce a mixture of structurally related compounds, of which
one or more are found in abundance. Advances in the chemical and biochemical sciences
from 1950s made possible the isolation and biological characterization of the main active
ingredients of all currently used pest control agents. Screening of fermentation broths for
antibacterial activity has resulted in the discovery of thousands of antibiotics, a few of
which have commercial utility.
19.9.1 Avermectins and Milbemycins
Avermectin and milbemycin groups of biopesticides are derived from a family of macro-
cyclic lactones produced by the novel soil actinomycetes Streptomyces avermitilis (Campbell
et al. 1983; Campbell 1989) and Streptomyces hygroscopicus (Takiguchi et al. 1983; Ono et al.
1983). They are among the most potent anthelmintic, insecticidal and acaricidal com-
pounds known. These compounds exhibited a broad spectrum of activities against agri-
cultural pests such as aphids, mites, caterpillars, intestinal worms, and other parasites
that prey on crops and ornamental plants. These are also used as veterinarian medicine
for the treatment of internal and external parasites and mites of pets and livestock. It has
a wide range of activities against lepidopteran pest species with LC 50 values ranging from
0.01 to 6 ppm against tobacco hornworm Manduca sexta , corn earworm Heliothis zea , and
southern armyworm Spodoptera eridania . In the commercial fermented culture of abam-
ectin (avermectin B1), avermectin B1a is the major component constituting 80%-85% of
avermectins and 15-20% avermectin B1b. While avermectin B1 is widely used as an agri-
cultural miticide, its 22,23-dihydro derivative ivermectin is used worldwide as a broad-
spectrum parasiticide in animals and humans. This semisynthetic derivative was the first
macrocyclic lactone developed and introduced commercially in 1981 for the treatment
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