In vitro effect of abamectin from Streptomyces avermitilis on the survival of the cyst nematodes Globodera pallida, Heterodera carotae and Heterodera schachtii

Abstract

The effect of an abamectin formulation (Vertimec© EC) was tested against the cyst nematodes Globodera pallida, Heterodera carotae and Heterodera schachtii in an in vitro hatching test. Abamectin (a mixture of two macrocyclic lactones B1a and B1b) is produced by the actinomycete Streptomyces avermitilis. Cysts of the nematodes were extracted from samples of infested soils by the Fenwick can and then subjected to different concentrations of an aqueous solution of the abamectin formulation (0, 1.125, 2.25, 4.5, 9.0, 18.0 and 36 g/ml) and exposure times from 24 to 384 hours. For each nematode specie batches of 50 cysts were set up and arranged in a growth cabinet (20°C ± 2) according to a randomized block design. Untreated cysts were used as control. There were three replications for each treatment. As natural and artificial hatching agents for H. carotae, H. schachtii and G. pallida were used carrot root leachate, 0.3 mM zinc chloride and 0.6 mM sodium metavanadate aqueous solutions, respectively. Every week emerged juveniles were counted. At the end of the hatching test cysts were crushed and unhatched eggs and juveniles counted. The total number of juveniles emerged in the hatching test were expressed as the percentage of the total egg content of the cysts (hatched + unhatched). From percentage hatch was calculated the mortality of each treatment considering the natural death in the control. Data of percentage mortality were subjected to probit analysis to calculate values of lethal doses (LD) required for 50% egg mortality. At 24 hours exposure, values of LD50 for H. carotae, G. pallida and H. schachtii were 9.9, 13.2 and 796 g/ml, respectively. For the same nematode species at 384 hours exposure LD50 decreased at 3.6, 2.9 and 17.6 g/ml.