Lethal effect of low pressure on the cigarette beetle
Low-oxygen (O2) controlled atmosphere (CA) is becoming used more commonly for disinfestation of stored tobacco. Generally, low-O2 atmospheres are achieved by nitrogen-purge. Practical CA chambers require approximately 24 h to reduce the partial pressure of O2 to lethal levels. Decompression is another means of reducing the O2 partial pressure. Lethal low pressures are achievable in much shorter periods of time using a vacuum pump. This study examined the lethality of low pressures on the cigarette beetle (Lasioderma serricorne) to verify the equivalence of low O2 and low pressures in terms of lethality. Tests were conducted in a temperature-controlled room (15-35 °C). Eggs, larvae, pupae, and adults were exposed to reduced pressure in vacuum desiccators (0.85 L). Desiccators were serially connected to a vacuum pump by polyurethane tubing. The air in the desiccators was evacuated to the target pressures (2.5, 5, or 10 kPa) with a vacuum pump. The desiccators were disconnected sequentially from the distal end and were vented at predetermined intervals. After treatment, viability of the insects was assessed. Results demonstrated that the highest lethality was achieved at 5 kPa. At this pressure level, the time necessary to achieve 99 % lethality in all growing stages (9.8 d at 20 °C; 7.0 d at 25 °C) was much shorter than low-O2 (0.5 %) treatment (35.6 d at 20 °C; 25.2 d at 25 °C). Susceptibility to low pressure varied among growing stages: eggs and pupae were the most tolerant; adults and larvae were less tolerant. Low-pressure treatment is not equivalent to low-O2 treatment because the most tolerant stages against low-O2 are opposite: adults and larvae. These results suggest that low-pressure and low-O2 treatment can be mutually complementary and that synergies can be created by combining these two treatments.