Phytochemical Analysis of Pyrethrum Plant Extract and its Anti-Aphid Effect On African Nightshades (Solanum Scabrum Mill)

Abstract

African nightshades (Solanum scabrum) are one of indigenous vegetables widely consumed in Kenya. Yield losses due to aphids are estimated to about 84-96% in Kenya. Aphids have developed resistance to synthetic pesticides. There is need to identify ecofriendly alternatives such as the use of botanicals like pyrethrum which are cheaper and safe to protect this potential vegetable specifically against insect pests which includes aphids, black-ants and white flies that severely reduce the yields. Plants secondary metabolites constitute a major source of bioactive substances. Pyrethrum extracts contain active ingredients which block the voltage gated sodium channels in nerve axon insects, resulting in a knockdown effect, hyperactivity, and convulsions hence death of insect pests. Little has been documented on the anti-aphid effect of pyrethrum leaf, flower and root extracts on aphids. Information on secondary metabolites in pyrethrum flower, root and leaf extracts is lacking. The objectives of this study were to determine the phytochemical constituents in pyrethrum flower, leaf and root parts and to determine the effect of different concentration levels of pyrethrum extracts on aphids affecting S. scabrum. The study was conducted at Maseno University farm. A field experiment was laid in Randomized Complete Block Design with three replications. Five treatments consisting of 0%, 33%, 67% and 100% pyrethrum flower, root and leaf extracts and duduthrin were applied. Phytochemical screening of extracts was carried out. Solanum scabrum seeds were locally sourced from the Botanic Garden, Maseno University, germinated and raised in 3m by 1m plots caged with mosquito net. After four weeks the seedlings were thinned to 9 seedlings per plot. Aphids (Aphis fabae) were obtained from International Center of Insect Physiology and EcologyNairobi were reared then introduced to every seedling (10 aphids) in all plots. Aphid population was determined weekly on leaves and by use of yellow water pan traps after treatment application. The data was subjected to analysis of variance and means were separated using Least Significant Difference at P ꞊ 0.05. The study revealed that pyrethrum flower, leaf and root extract contained phenols, saponins, alkaloids, flavonoids, tannins and phytosterols. Triterpenoids were absent in the leaf extracts. Phenols, flavonoids and triterpenoids were more in flowers than in root and leaf extract. The root exhibited more amounts of saponins, alkaloids and phytosterols. Aphid population was significantly (p≤0.05) reduced in all plant treated with pyrethrum extracts. Outstanding concentration were 100% and 67% pyrethrum flower and root extracts which recorded zero number of aphids on day 69th, 76th and 83rd day but leaf extracts showed a reduced effect. The use of 100% pyrethrum flower or root extracts is recommended to farmers in aphid control so as to realize improved yield and production of S. scabrum in order to reduce the overdependence on synthetic pesticides