Botanical insecticides have long been touted as attractive alternatives to synthetic chemical insecticides for pest management because botanicals reputedly pose little threat to the environment or to human health. The body of scientific literature documenting bioactivity of plant derivatives to arthropod pests continues to expand, yet only a handful of botanicals are currently used in agriculture in the industrialized world, and there are few prospects for commercial development of new botanical products. Pyrethrum and neem are well established commercially, pesticides based on plant essential oils have recently entered the marketplace, and the use of rotenone appears to be waning. A number of plant substances have been considered for use as insect antifeedants or repellents, but apart from some natural mosquito repellents, little commercial success has ensued for plant substances that modify arthropod behavior. Several factors appear to limit the success of botanicals, most notably regulatory barriers and the availability of competing products (newer synthetics, fermentation products, microbials) that are cost-effective and relatively safe compared with their predecessors. In the context of agricultural pest management, botanical insecticides are best suited for use in organic food production in industrialized countries but can play a much greater role in the production and postharvest protection of food in developing countries.

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Botanical insecticides, deterrents, and repellents in modern agriculture and an increasingly regulated world

Bioactivity of the essential oil extracted from Evodia rutaecarpa Hook f. et Thomas against the grain storage insects, Sitophilus zeamais Motsch. and Tribolium castaneum (Herbst).

https://www.srs.fs.usda.gov/pubs/ja/ja_lee001.pdf

Fumigation toxicity of monoterpenoids to several stored product insects

Repellent and insecticidal activities of essential oils from Artemisia princeps and Cinnamomum camphora and their effect on seed germination of wheat and broad bean.

Biologists in the early part of the 20th century believed that since the secondary sexual characteristics of insects were unaffected by castration, insects did not secrete hormones. This view was challenged by the conclusive experiments of Stephan Kopec in 1917, who showed by surgical maneuver, that insect metamorphosis was under the hormonal control of the brain. Over the next half- century, significant discoveries in insect endocrinology were made by such pioneers as Wigglesworth, Bodenstein, Fukuda, and Williams, among others (see review by Granger and Bollenbacher 1981). The classical scheme that was developed by these scientists was that a hormone from the brain, now known as prothracicotropic hormone (PTTH), stimulated the prothoracic glands to release a molting hormone (ecdysteroid), which caused either molting or metamorphosis depending upon the stage of the insect, and in particular, on whether a third hormone, juvenile hormone (JH), was present.

Insect growth regulators

Repellency and toxicity of azadirachtin (98% AZA, which contains 98% azadirachtin) and 3 neem extracts (48, 23, and 7% AZA) to 3 stored-product insects, the rusty grain beetle, Cryptolestes ferrugineus (Stephens), the rice weevil, Sitophilus oryzae (L.), and the red Aour beetle, Tribvlium castaneum (Herbst), were investigated in the laboratory. Each test material repelled all 3 species in a standard repellency test using a food preference apparatus. Significant negative correlations were found between insect settling response and extract concentrations. T. castaneum was more sensitive to the repellent action of neem than the other 2 species. The test materials were also toxic to the 3 pest species, with C. ferrugineus being the most susceptible. Six-week LC50 values for 48, 23, and 7% AZA for C. ferrugineus were 18.8, 37.0, and 127.3 ppm, respectively. The F1 adults of all 3 insect species in almost all treatments were significantly reduced compared with controls. This reduction was significantly dose dependent. The relationship between bioactivity of neem materials and their azadirachtin content was established and is discussed. We confirmed that azadirachtin was largely responsible for both repellent (behavioral) and toxic (physiological) actions of neem on stored-product insects. However, the neem extracts are slightly more active than pure azadirachtin when applied at equivalent azadirachtin concentrations, indicating that azadirachtin is not the only active compound in neem.

Y.S. Xie

Papers

Repellency and toxicity of azadirachtin and neem concentrates to three stored-product beetles

Repellent effect of pea (Pisum sativum) fractions against stored-product insects.

Insecticidal activity of Melia toosendan extracts and toosendanin against three stored-product insects