The effects of aldicarb, a nematicidal carbamoyloxime, and its oxygen analogues on soil and plant parasitic nematodes

Abstract

The effects of aldicarb and its two major toxic breakdown products, aldicarb sulphoxide and sulphone have been investigated using several species of nematode. Of the three compounds, aldicarb was the most effective, reducing nematode hatch in water and soils, their dispersal on treated agar and locomotory activity. Meloidogyne incognita larvae accumulated in treated pot soils and their invasion of host plant roots was delayed. In soils the contact of nematodes with a paralysing dose of the non-volatile nematicide or its sulphoxide is of fundamental importance in nematode control. In tomato roots the reduction of meloidogyne invasion can only be attributed to the persistence of minor amounts of the sulphone derivative. Control of invasion by the retention of toxic residues in roots is less effective since aldicarb and its breakdown products accumulate in the foliage. The movement patterns of second stage Meloidogyne and Heterodera larvae altered in the presence of these carbamoyloximes from open to closed spiralling, the tracks becoming increasingly tortious with exposure. Contracted paralysis of nematodes resulted, especially with aldicarb and its sulphoxide, the nematodes becoming almost motionless. When the nematicide treatments were discontinued, nematodes regained their activity. Recovery was generally more rapid after sulphoxide or sulphone treatment. Of the three compounds, aldicarb had the greatest affect on stylet movement, stimulating abnormal protraction except in Xiphinema. Maximum stylet protraction corresponded with maximum body inactivity. The permeation of two nematode species by C - labelled aldicarb was investigated. These were permeable to aldicarb which accumulated within them. An equilibrium was reached between the nernaticide inside the nematode and that in the exposure solution. After penetreation the parent compound was rapidly converted to its sulphoxide and subsequently to the corresponding oxime and nitrile. The egress of labelled sulphoxide from treated Panagrellus was slow. The results obtained in these investigations are compared with relevant published data.