Influence of herbicides on lipid reserves, mortality and infectivity of Heterorhabditis amazonensis (Rhabditida: Heterorhabditidae)

Abstract

Infective juveniles (IJs) of entomopathogenic nematodes show reduced infectivity when their lipid content decreases. The expenditure of this energy reserve can be accelerated by stress factors, such as contact with chemical pesticides. The aim of this study was to correlate the amount of lipids in Heterorhabditis amazonensis IJs with their mortality and infectivity after exposure to solutions of the herbicides clomazon + hexazinon (Ranger), at the rate of 0,0027 g, and of simazine + ametryn (Topeze) at the rate of 0,0054 ml, in 200 ml sterilized distilled water (equivalent to 4 kg/ha of Ranger and 8 l/ha of Topeze). Nematodes in distilled water were used as a control. Nematode mortality was evaluated by observing 1,000 IJs randomly. Infectivity was evaluated by inoculating 1 ml of nematode suspension on Galleria mellonella larvae. Lipids in IJs were stained with “Oil Red O” dye, mounted on slides, and photographed with a trinocular microscope. The area corresponding to the lipid reserve was measured with the “Image Tool” software. The results showed that the herbicides did not kill H. amazonensis IJs after 5 days exposure to them, nevertheless they reduced IJ infectivity. The amount of lipids in IJs exposed to the herbicides was smaller than in IJs kept in water and appeared to be correlated with reduced infectivity.