Natural insecticides based on extracts from seed kernels of the neem tree, Azadirachta indica A. Juss (Meliaceae), have gained importance for pest management in the last decades. Due to the public pressure to eliminate synthetic chemical pesticides, biological products for pest management are considered as a promising alternative. Neem products are especially convenient for home and garden use and for high-value crops such as ornamentals. Their low persistence in the environment and low mammalian toxicity (Sundaram, 1996; Raizada et al., 2001;Boeke et al., 2004;Kleeberg, 2004) are advantageous for use in public areas. One common pest of roses is the rose aphid, Macrosiphum rosae L. (Hemiptera: Aphididae). It has an almost global distribution and infests all sorts of Rosa species as its primary host plant. In Europe, M. rosae can be found on roses from spring to autumn. Preferred feeding sites are young leaves and developing buds. Severe
Many studies in the last decades addressed the antifeedant and repellent effects of neem (Azadirachta indica)-based pesticides on arthropod herbivores with azadirachtin as the leading active ingredient. However, results for aphids regarding repellence and feeding were often contradictory and mainly based on laboratory studies with self-made neem extracts in high concentrations. Moreover, no data are available on the presence of azadirachtin in the phloem of treated plants—the tissue that most aphids feed on. We investigated how the application of the commercial neem product NeemAzal-T/S onto only one plant half (upper or lower) affects nymphs of the aphid Macrosiphum rosae in clip cages on the untreated plant half. Results for aphid mortality indicate that active ingredients of NeemAzal-T/S are translocated both upwards and downwards in rose plants and that active ingredients are transported in the phloem. Furthermore, we investigated whether NeemAzal-T/S has a repellent or antifeedant effect on M. rosae. A choice test in the greenhouse as well as the quantification of honeydew excretion and electrical penetration graph analysis do not show differences in settling or feeding on untreated and NeemAzal-T/S-treated rose plants. Collectively, our data show that the effect of approved concentrations of NeemAzal-T/S on M. rosae is based on the toxicity after feeding on treated plants, not on starvation.
Natural insecticides often do not provide a strong knock-down effect and have a lower efficacy than synthetic pesticides. For an effective application of natural insecticides, it is essential to know the product's mode of action in detail. The efficacy of the commercial neem product NeemAzal-T/S and its influence on stage specific mortality, development and reproduction of rose aphids, Macrosiphum rosae, were determined in greenhouse trials. NeemAzal-T/S had an efficacy of 40 % against M. rosae in standard efficacy trials with initial infestations between 100 and 270 aphids per plant. However, it has a significant impact on the survival of nymphs in the first to third instar as well as on the development. Nymphs treated with NeemAzal-T/S exhibit a significant delay in molting to the second instar and most of them die before the first molt. Furthermore, reproduction of adult M. rosae females is reduced when aphids are exposed to sub-lethal concentrations of neem already as first instars. The increase in population growth is inhibited or delayed on rose plants treated with NeemAzal-T/S. The results indicate that applications of NeemAzal-T/S can be used for controlling rose aphids in integrated pest management (IPM). Due to a lack of a rapid knock-down effect and no effects on adult aphids, combinations with natural enemies of pest insects as well as with other insecticides are possibilities to enhance the efficacy.
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