Insect-killing activity

Lepidopteran insect-killing Bacillus sphaericus with no mosquitocidal activity and a novel insecticidal factor (H. Nishiwaki, Kinki Univ., Japan)... 

Recombinant Baculoviruses Expressing Insect Toxins. The first attempt to modify a NPV for increased insecticidal activity was conducted by Carbonell et al 33) in which an insect-specific toxin (BelT) from the scorpion Buthus eupus was incorporated into the AcNPV genome. Although low levels of toxin expression were confirmed, the recombinant NPV did not result in quicker killing rates of host insects. Failure to improve killing activity may be due to an insufficient level of toxin expression by AcNPV, an incorrect sequence of toxin DNA, and/or insufficient or incorrect folding of the toxin following expression. 

Bacillus thuringiensis produces a variety of organic compounds which are toxic to the larvae of certain susceptible insect hosts. Among the toxic entities are proteinaceous crystals, probably three soluble toxins, and certain enzymes. The protein material is the major toxin active in killing lepidopterous larvae. The protein is formed by the cells apparently in close synchrony with sporulation, and its nature is a constant function of bacterial strain. The mode of action of the protein is under study. The sequence of events in the pathology observed is probably solubilization of the crystal (enzymatic or physical)—>liberation of toxic unit—>alteration of permeability of larval gut wall— change in hemolymph pH—>invasion of hemolymph by spores or vegetative cells of the bacterium. 

This requirement is obvious, but one point should be recognized. The term effective refers to practical control and not necessarily to kill. The aim is the maximum of quality of product and maximum productivity of the host plant through the prevention of damage by the pest. If we can accomplish this by interference with the activities of the pest, such as prevention of multiplication or prevention of invasion, it is as satisfactory as the kill of the individual insect. 

At first, Geigy s biologists were puzzled because the insects sprayed with DDT did not die immediately. Accustomed to the quick action of pyrethrum and rotenone, they dismissed Muller s discovery as unimportant. They did not realize that DDT s long period of activity could be far more important than sheer speed. In the parlance of insecticides, DDT had slow knockdown but sure kill. Surfaces sprayed with DDT in 1941 and stored under dust-free laboratory conditions were still toxic to insects seven years later. 

Parasitoid wasps are the most widely studied group of insect parasites. Female wasps lay an egg(s) on or in an insect and the progeny develop utilizing that insect as their sole food source, eventually killing the host. Female parasitoids tend to be host specific and typically exploit a specific host immature life stage (e.g., egg, larvae, or pupae). Most parasitoid wasps are relatively small. Females actively seek out multiple hosts and can find and parasitize host insects in cryptic habitats. There is a wide range of species that attack stored-product insects and a considerable body of research on these natural enemies, only some of which are covered here [see Godfray (1994) for more information on parasitoids and Brower et al. (1995) and Scholler and Flinn (2000) for reviews of information specifically on stored product parasitoids]. 

Insecticides are derived from petroleum oil, which can usually be applied in water-emulsion form and which have marked killing power for certain species of insects. For many applications for which their own effectiveness is too slight, the oils serve as carriers for active poisons, as in the household and livestock sprays. 

Protecting garden friends Even organically approved pesticides are nonselective and will kill both harmless and helpful insects as well as the target pest. Always spray in the evening, when bees are not active, and never spray on a windy day when the pesticide might drift. 

Polyacetylenes are toxic to a broad range of organisms (39) but are especially toxic to insects. At 0.5 ppm, 9 of 14 compounds tested were toxic to first instar mosquito larvae (Aedes aegypti) in 30 min treatments with sources of near UV (15 W/m ) (40). The compounds were more active in sunlight. For example CX-T killed second instar larvae Instantaneously at 4 ppm. Compounds VTI, Ct-T and PHT were especially active and were selected for further testing in dose response experiments (41). For similar near UV treatments, the LC50 for a-T was 19 ppb,... 

And one must first of all consider the species of insect or insects involved, the stage they are in and to what extent they are known or expected to be hidden, whether they are active, sluggish, free flying, or crawling. Therefore, decision must be made as to whether the fogging is to be strictly spatial in intent, or whether residual effect is necessary to produce the desired kill and control. 

Insects and mites are animals and, traditionally, the most effective compounds for their control have been compounds that interfere with nerve function. Fundamentally, all animals have the same mechanisms for detecting and transmitting nerve impulses. Nerve-active compounds that kill insects will usually have some effects on mammals. 

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