Fumigant Toxicity of Eucalyptus camaldulensis and Callistemon viminalis Essential Oils against Tribolium confusum

Eucalyptus camaldulensis Dehnh and Callistemon viminalis (Gaertn) essential oils were tested against adults (1-3 day old) of Tribolium confusum Jacquelin du Val. in 280 ml glass vials either with or devoid of wheat grains. The oils were also examined for fumigant toxicity against, 5 and 20-day-old larvae. The essential oils were obtained through hydrodistillation, applying a modified Clevenger type apparatus. Experiments were carried out at 27±1°C and 65±5% R.H. under dark conditions. Results of fumigant toxicity tests indicated that mortality increased with increase in concentration and time. Lethal concentration of E. camaldulnsis and C. viminali 50% of adults (LC50) were estimated as 20.88 and 20.06 µL/L air, respectively. Lethal times to kill 50% of adults (LT50) at concentrations of 35.71, 32.14, 28.57, and 25 µL/L air lasted 20.59, 15.94, 14.35 and 13,39 h for E. camaldulnsis oil whereas 17.57, 14.46, 11,69, and 10.72 h for C. viminalis, respectively. The most sensitive stage was 5-day-old larvae followed by adults of T. confusum, while 20-day-old larvae were highly tolerant to the tested essential oils. The lethal effect activity of the essential oils decreased significantly in jars filled with wheat kernels. LC50 values of E. camaldulnsis, and C. viminalis to kill T. confusum adults were 878.50, and 741.27 µL/L air, respectively; showing the low fumigant efficacy of the oil in the presence of grain. This may be due to a considerable sorption of essential oil by wheat grains and insufficient permeation of the oil vapor into seed inter-spaces.