[15] Howard, L. O., and Popenoe, C. H. Hydrocyanic-acid gas against household insects. U. S. Dept. Agr. Farmers' Bul. 699. 8 p. 1916.
The fumes of burning sulphur are also a very efficient means of control where the conditions are such that this method can be used, readily destroying the insect in all stages, including the egg. The treatment is inexpensive compared with the use of hydrocyanic-acid gas and offers much less risk of danger to human beings. There is, however, a considerable risk of injury to household fabrics, furnishings, and wall papers from the strong bleaching quality of sulphur fumes. This danger will be somewhat diminished if the fumigation can be done at a time when the room or house is thoroughly dried out, as in winter by a furnace or other heating system. Further precautions should be taken by removing all metallic surfaces from the room or building, or by protecting them with a coating of vaseline. Two pounds of sulphur are recommended for each 2,000 cubic feet of space, and the building should be closed for the treatment for at least 5 or 6 hours, or preferably for 24 hours. Sulphur candles may be used where available, or the sulphurous gas or fumes can be generated by burning the sulphur in a dish placed in the center of the room, and for protection set within a larger vessel. Thorough-going precautions must be taken to prevent accidental overflowing or the starting of a fire, and after the fumigation the house should be given a thorough airing.
Other gases have been experimented with, such as formalin and the vapors of benzine, naphthaline, and camphor, but these gases are of little value. Similarly, insect powders are of little value, largely from the difficulty of getting them into the crevices and other places of concealment of the insects.
Where the use of poisonous gas is difficult or objectionable, especially if only one room is infested, the pests may be eliminated by the application of kerosene, benzene, or any of the lighter petroleum oils, by means of a small hand sprayer. The liquid should be directed at close range into all cracks and crevices in the walls and behind loose wall paper. Open spaces back of baseboards and picture moldings should be liberally treated. The bedstead and springs should receive the same attention, care being taken to spray the liquid into all crevices. The mattress should likewise be carefully gone over. All seams and spaces beneath tuftings should be thoroughly dosed. At the expiration of 10 days the entire treatment should be repeated with the same care, regardless of whether any bugs are seen or not. If the two applications are made with painstaking care this should be sufficient for complete eradication.
Temperature control.—The possibility of temperature control is indicated in the discussion elsewhere of the effect of temperature on this insect. A temperature maintained below freezing for 10 or 15 days destroys the eggs, and this temperature continued for 15 days to a month will destroy the newly hatched young. It may be, therefore, that if infested houses in cold climates should be opened up and allowed to remain at a temperature well below freezing for a considerable period, all eggs and the young, and possibly most if not all of the adults, would be exterminated. This method of control might perhaps be practicable at least in the case of summer houses in the north which are left untenanted in the winter.
The maintaining of high temperatures may be an even more efficient method of control. The activity of the bedbug is at its greatest between 60° and 70° to 75°. As indicated elsewhere, in a temperature of 96° to 100° F., accompanied with a high degree of humidity, newly hatched bedbugs perish within a few days, and, if this temperature is raised to 113° F., in a few minutes. A temperature of 113° will also destroy the eggs, and with these higher temperatures the item of humidity is not apparently important.
A very practical test of this method of control was made in Ontario, Canada, by the Dominion Entomological Department,[16] adapting the method of control of insects infesting granaries and flour mills by superheating. In this instance an eight-room, two-story frame house, badly infested with bedbugs, was during the month of July brought to a very high degree of heat by making up good fires in the heating furnace and other stoves in the house and closing up the house to retain the heat. Recording thermometers placed in different rooms indicated a gradual rise of temperature from 77° to 160° during the period from 9.30 in the morning to 7.30 in the evening, the outside temperatures during the same period ranging from 64° to 73° F. At 1.30, when the temperature in the different rooms ranged from 109° to 130°, many adults and immature forms had already succumbed. By 4.30 the temperature was ranging from 127° to 148° in different rooms, and all the insects were dead. The continuation of the experiment was on the supposition that it would probably require a higher degree of temperature to destroy the eggs. The eradication of the bedbug from this house was complete, and no damage was done to the house or its contents. That the temperatures ranged much higher than was necessary is indicated by the temperature experiments referred to elsewhere, which indicated that the eggs as well as larvæ are destroyed within a few minutes at a temperature of 113° F. The latter temperature was also sufficient to destroy quickly the adults of fleas, cockroaches, and other insects. It would seem, therefore, that superheating of houses in midsummer to a temperature of 120° to 130° F. may prove to be one of the simplest and most effective means of eradication of this and perhaps other household pests.
[16] Ross, W. A. Eradication of the Bedbug by Superheating. In Canadian Entomologist, vol. 48, No. 3, pp. 74-76. 1916.