In an attempt to specify the time of insect contamination, we investigated the histological changes of cockroach muscle cells and tissue with elapsed time after death. Effects of various treatments such as hot water or alcohol soaking were also examined. Slight but clear histological changes were observed by microscope in the muscle cell and tissue even within 15 minutes after death. In particular, muscle fibers began shrinking, and nuclei and sarcoplasm gradually became more difficult to detect within 60 minutes after death. Hot water or alcohol soaking treatments also brought about prominent histological changes, which differed significantly from the non-treated control. These results suggested that histological examination of invading insects might be an effective procedure for estimating the time of insect contamination.

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Carbon dioxide (CO₂) was introduced into polyethylene chamber with the caged roof rats, Rattu rattus, inside a laboratory to examine its efficacy against them. When the gas was introduced at 50 liters/min. for 90 minutes into a 9.2 m³ volume at 20℃, all four rats caged on the floor level died within 25 minutes after gas release. However, all rats in the middle part (90 cm height) and upper part (180 cm) could survive for 80 minutes. In this case, the gas concentration rapidly reached 70% in 30 minutes. after gas release into the cage on the floor level. At that time, however, the gas concentrations in the middle and upper sites were 21% and 0.5%. After 90 minutes, an electric fan circulated the air, and the gas concentration became a uniform 47% throughout the chamber and paralyzed all rats. When the gas concentration was increased to 150 liters/min. all rats were knocked out within 130 minutes after gas circulation. The recommended CO₂ gas concentration for controlling rats is therefore 60% for 40 minutes.

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Preferences of the dark-brown ant, Lasius japonicus for several building materials were tested. The preference ratios for natural deterioration fir timber were 55.0% under dry conditions, 58.3% under wettish conditions, and 61.5% under wet conditions. Dark-brown ants exhibited low preference ratios (0.3% to 3.6%) for new and rotten timbers under the same conditions. They exhibited the highest preference ratios for polystyrene insulation (33.3% under dry conditions and 31.5% under wettish conditions) and preference ratios of 28.6% for glass wool and 24.8% for polyurethane under wettish conditions.

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