Otiorrhynchus Ligustici L. (Coleptera: Curculionidae) Ii. Method for Determination of the Degree of Damage by Larva and Biochimical Composition of the Root System in Different Alfalfa Varieties

Abstract

(Obraztsov Chiflik, Ruse). For determination of the damage from the large alfalfa weevil Otiorrhynchus ligustici on the root system of plants was developed methodology depending on the root area and the damage area. The area of the roots was calculated by the formula S = (π * d * L) / 2, where π is 3.14; d-diameter of the root collar, L-length of the root. The area of the furrows оn the root system was product of length and width of the furrows. With the lowest percentage of furrows and tolerant to O. ligustici were Multifoliate, Prista 2 and Europerespectively 10.38, 11.41 and 11.68%. Highly sensitive, with high percentage of damage were distinguished Dara, Prista 4 and Prista 3 (respectively 14.28, 14.05 and 13.58%). As a result of the caused damage the content of sugars and saponins increased as depending on the sensitivity of varieties the increase was different. In the tolerant varieties to the pest the increase in sugar content was less pronounced, but in the sensitive ones-stronger. In regard to the saponins the trend was reversed-the increase in the sensitive varieties was less and in the tolerant varietiesstronger which could be explained with the defensive reaction of plants to compensate the losses from damages of the pest.