The influence of the lucerne bud mite (Eriophyes medicaginis Keifer) on the growth of lucerne

Abstract

The influence of Eriophyes medicaginis on the growth of lucerne (Medicago sativa L.) was studied at four temperatures (15, 20, 25 and 29¦C) at an initial infestation level of 10 mites per seedling, and at two temperatures (20 and 29¦C) with four initial levels of infestation (2, 5, 10 and 20 mites per seedling). At 25¦ and 29¦C, infestation with 10 mites per seedling significantly reduced dry weight of tops, stem length and the development of axillary shoots within 22 days of infestation. In this period, the numbers of mites increased 16-fold at 29OC, ninefold at 25¦C and sixfold at 20¦C, but there was no increase at 15¦C. The extent of damage caused by mites at 20¦C appeared to vary with the differences in growth of the plants under different photoperiods. Under a short photoperiod (10.3 h) where no axillary shoots developed on either infested or control plants, the extent of damage due to mite infestation was much higher than under a longer photoperiod (13.2 h) where axillary shoots developed on all seedlings. Damage symptoms on leaves of infested plants included chlorotic patches (mainly at 20¦ and 25¦C), agate-like banding (29¦C) and a waxy mottle (15¦C).