Biopesticides - Pesticides: Evaluation of Environmental Pollution - page 596

activity is evident for 7-10 days or longer, depending on the insect and the application rate
( Farm Chemicals Handbook 1995; Thomson 1992).
Azadirachtin is used to control whiteflies, aphids, thrips, fungus gnats, caterpillars,
beetles, mushroom flies, mealybugs, leaf miners, gypsy moths, and others on food, green-
house crops, ornamentals, and turf (Thomson 1992).
19.8.3 Rotenone
Rotenone is a naturally occurring chemical with insecticidal, acaricidal (mite and spider-
killing), and piscicidal (fish-killing) properties, obtained from the roots of several tropical
and subtropical plant species belonging to the genus Lonchocarpus or Derris . It is a selective,
nonspecific insecticide, used in home gardens for insect control, for lice and tick control
on pets, and for fish eradications as part of water body management. Both a contact and
stomach poison to insects, it kills them slowly, but causes them to stop their feeding almost
immediately. It exerts its toxic action by acting as a general inhibitor of cellular respiration.
Rotenoids, the rotenone-related materials, have been used as crop insecticides since
1848, when they were applied to plants to control leaf-eating caterpillars. However, they
have been used for centuries (at least since 1649) in South America to paralyze fish, caus-
ing them to surface (5). Derris root has long been used as a fish poison and its insecticidal
properties were known to the Chinese well before it was isolated by E. Geoffrey in 1895.
The use of the ground root of certain species of Derris was patented in 1912, since when it
has been established that the active compounds are rotenoids, of which the main insecti-
cide is rotenone.
Rotenone is a mitochondrial poison, which blocks the electron transport chain and pre-
vents energy production (Hollingworth et al. 1994). As an insecticide, it is considered a
stomach poison because it must be ingested to be effective. Pure rotenone is comparable
to DDT and other synthetic insecticides in terms of its acute toxicity to mammals (rat oral
LD 50 is 132 mg/kg), although it is much less toxic at the levels seen in formulated products.
19.8.4 Sabadilla
Sapodilla is a botanical insecticide obtained from the seeds of the South American lily
Schoenocaulon officinale. . In purity, the active principals, cevadine-type alkaloids, are
extremely toxic to mammals (rat oral LD 50 is 13 mg/kg), but commercial preparations typi-
cally contain less than 1% active ingredient, providing a margin of safety. The mode of
action of these alkaloids is remarkably similar to that of the pyrethrins, despite their lack
of structural similarity.
19.8.5 Ryanodine
Ryanodine, the toxic principle of the roots and stems of the shrub R. speciosa , has a wide
spectrum of activities against many insect pests. It is relatively nontoxic to mammals and
is capable of controlling important larval lepidopteran pests at 3-16 g alkaloid equivalents
per acre, making it one of the most potent natural insecticides. At least eleven ryanoids
have been isolated and characterized from various Ryania extracts (Ruest et al. 1985;
Jefferies et al. 1991, 1992a,b). Structurally related ryanodines active against Macaronesia
fortunata and Helicoverpa armigera have also been reported from Persia indica (Gonzalez-
Coloma et al. 1990, 1993, 1996). Ryanodines reportedly affect insect muscles by binding to
the calcium channels in the sarcoplasmic reticulum. This causes calcium ion flow into the