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Effects of extracts from Neem, Azadirachta Indica (A. Juss.), on aphids (Homoptera:Aphididae) with respect to their control

University of British Columbia

Laboratory and field trials with formulated neem seed oil (NSO) and neem seed extract (NSE) demonstrated that these materials are potentially very effective as aphicides. Sprays of NSO to plants in the laboratory resulted in significant reductions in numbers of green peach aphids, Myzus persicae (Suizer), on pepper and rutabaga; lettuce aphid, Nasonovia ribisnigri (Mosley), on lettuce; and strawberry aphid, Chaetosiphon fragaefolii (Cockerell), on strawberry. Under field conditions, NSO and NSE were as effective or better than the commonly used botanical insecticide pyrethrum for the control of aphids on pepper, cabbage, and strawberry, but they were ineffective for the control of aphids on lettuce. Leaf disk choice bioassays to assess the deterrency of neem to aphids produced variable results, and NSO at concentrations from 1 to 2% were deterrent to only half the species tested. Differences in behavioral response of aphids to the various volatile and non—volatile components of neem likely explains, at least in part, the contradictory and inconclusive results from previous studies. Deterrency of NSO to C. fragaefolii was lost after 24 hours following applications to strawberry in the greenhouse, suggesting that the antifeedant or repellent action of neem is of limited value for the control of aphids or the plant viruses they transmit. In laboratory bioassays to determine the toxicity of neexn to aphids, NSO applied to leaf disks at a concentration of 1.0% resulted in 94 to 100% mortality of second instar N. ribisnigri, M. persicae, and C. fragaefolii after nine days. The equivalent amount of purified AZA (40 ppm), considered to be the most active ingredient of neem, was as effective as NSO toward N. ribisnigri and M. persicae, but survival of C. fragaefolii was unaffected by AZA even at twice that rate. Although survival of adults was not reduced by exposure to NSO or AZA, survival of offspring from treated adult M. persicae and N. ribisnigri was reduced significantly. The effective concentration of AZA resulting in 50% mortality (EC 50) after nine days ranged from as low as 2.4 ppm for M. persicae on pepper, to 635 ppm for C. .fragaefolii on strawberry. The growth-disrupting effect of AZA towards M. persicae was influenced by the host plant and the nymphal instar studied. For example, the E5C0 f or second instars on corn was more than 20 times higher than on mustard cabbage, while fourth instars were approximately 20 times less sensitive than first instars. In addition to direct toxicity, nymphs exposed to NSO or AZA that successfully molted to adults were often smaller and possessed physically deformed wings, legs, and stylets. Exposure of adult N. ribisnigri and M. persicae for three days to 1.5% NSO applied to leaf disks resulted in the production of 76% and 83% fewer live offspring, respectively, compared to controls over a one week period. The effective concentration of AZA resulting in the production of 50% fewer offspring (EC 50) for eight species of aphids ranged from as low as 14.4 ppm for N. ribisnigri on lettuce to 616.4 ppm for Rhopalosiphuni padi (L.), the bird cherry—oat aphid, on corn. The decrease in aphid reproduction resulted from the production of fewer offspring and an increase in the number of embryos that failed to complete development and were dead (embryonic) at birth. Laboratory studies indicated that exposure to neem reduced the survival of aphid predators, Coccinella undecimpunctata (L.), and Eupeodes fumipennis (Thompson), and parasitoids, Aphidius sp., but foliar applications of neem did not cause significant harm to natural enemy populations in the field, demonstrating that neem- based insecticides are potentially compatible with integrated pest management programs. Neem provides effective control of aphids, while causing little damage to beneficial insects, man, or the environment.

Thesis/Dissertation

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2008-12-17

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http://hdl.handle.net/2429/3023

Plant Science

University of British Columbia

UBCV

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