The toxic action of pesticides on ants in the treatment of a forest depends on the kind of insecticide, the form of it, and the dose of its application. For example, the treatment of a forest with a 25 per cent mineral oil emulsion of HCH in a dose of 15 kg/ha affected the ants insignificantly. Only those specimens perished that came into direct contact with the pesticide during treatment or with the treated surface during the first day after the treatment.
In the overall treatment of a forest with pesticides, the self-protection of ants exhibits itself when they leave the treated surface for their anthill.
Bees are killed most frequently when during treatment the pesticides are carried away onto areas with blossoming plants.
The danger of poisoning bees depends on the properties of the compounds. Stomach pesticides are very harmful to bees. They get into an insect through nectar, pollen of the plants, or with water. The most dangerous among the contact insecticides are those penetrating through the chitin. The bee has the most developed nervous system of all insects, therefore it is the most sensitive to insecticides affecting the nervous system. Formulations based on polychloroprene or toxaphene have a low toxicity to bees.
Laboratory tests have shown the high stomach toxicity of carbaryl and trichlorfon in bees. The lethal dose of these pesticides is much smaller than the concentrations used for protecting plants. The contact action of carbaryl on bees is 9.8 times greater than that of trichlorfon. Carbaryl may cause the death of 90.4 per cent of all bees and persist for three or four days. Beauverin is also dangerous to bees. This biological formulation causes the death of bees for a rather long time after its application (three weeks).
In addition to the direct danger of the insecticides used, it must be borne in mind that these substances may appreciably weaken bees’ organisms and promote their infection with bee pests. The toxic action of pesticides on bees depends on the periods and ways of application. Most fungicides and herbicides are only slightly or not dangerous to bees. The use of even the most toxic pesticides in the form of aerosols in the early spring in the absence of blossoming plants does not harm bees.
The main causes of the mass poisoning of bees by toxicants are the absence of strict planning of measures for the chemical protection of plants and the failure to observe the rule of giving 3-5 days’ notice of treatment indicating the specific time, place, and nature of the scheduled chemical treatments of plantings of agricultural crops. It is dangerous to treat plants with poisonous chemicals in the daytime when the mass flight of bees takes place, and it is also dangerous to treat large bodies of entomophilic plants in the blossoming stage with pesticides that have a prolonged residual action.
Bees also become poisoned when the treated fields are directly adjacent to plantings of blossoming honey plants. The poisoning of bees is noted more frequently in aerial spraying at a wind velocity exceeding two m/s.
With a view to the toxicity of pesticides to bees and the duration of their persistence, it is necessary to select the substances so that their residues will be completely decomposed before the plants blossom. The presence of pesticide residues on blossoming plants even in amounts not toxic to bees leads to their accumulation and concentration in the honey.
To protect bees from the action of pesticides, chemical treatment must be carried out in the evening or early morning. During the treatment, the bees must be isolated or removed elsewhere.
The isolation period depends on the features of the pesticide used. When employing a lime-sulphur concoction, sulphur, or blue vitriol, bees should be isolated during the period of treatment; when employing Bordeaux mixture, copper oxychloride, 2,4-D, toxaphene, fol-pet, tetradifon, monuron, fenuron, dalapon—up to 5-6 hours after treatment; when employing zineb, captan, simazine, nitrafen, chlorpropham, atrazine, polychloroprene—for one day; when employing malathion, parathion-methyl, menazon, barban, trichlorfon, DNOC, the bees should be isolated for two days.
If plants are being protected by using HCH, carbaryl, heptachlor, and dimethoate, the isolation period is increased to 3-4 days. In zones with a low temperature and an increased humidity of the air, the periods of isolation are increased by 1-2 days.
The author is an associate professor (retd.) and former head of the department of botany at Ananda Mohan College.