The aim of the current study was to evaluate the fumigant activity of the essential oils from 11 species of the genus Eucalyptus and two of their hybrids on first instar of Blattella germanica L. The fumigant activity and repellence of the four major monoterpene components of these essential oils also were tested. Fumigant activity was evaluated by exposing nymphs to the vapors emitted by 50 µl of essential oil or monoterpene in a closed container. The lowest knockdown time 50% (KT50) values, expressed in minutes, were elicited by the essential oils of the Eucalyptus grandis × Eucalyptus tereticornis (57.9) hybrid, Eucalyptus sideroxylon A. Cunn (62.0), E. grandis × Eucalyptus camaldulensis (63.8) hybrid, Eucalyptus viminalis Labill (64.1), Eucalyptus dunnii Maiden (64.5), and Eucalyptus grandis (Hill) ex Maiden (68.7). The KT50 values for the remaining essential oils ranged between 74.5 (E. saligna Smith) and 161.4 min (E. tereticornis Smith). The essential oil from the hybrid E. grandis × E. tereticornis was 3.7 times less toxic than dichlorvos (positive control). The KT50 values of monoterpenes were 38.8 for α-pinene, 55.3 for 1,8-cineole, 175.6 for p-cymene, and 178.3 for γ-terpinene. α-Pinene was 2.5 times less toxic than dichlorvos. There was a strong positive correlation between the fumigant activity of essential oils and their corresponding 1, 8-cineole and α-pinene concentration. Repellency was quantified using a video tracking system. Two concentrations of monoterpenes were studied (7 and 70 µg/cm2). All compounds produced a light repellent effect but only when applied at 70 µg/cm2. In all cases, the repellent effect was less than that produced by the broad-spectrum insect repellent N,N-diethyl-3-methylbenzamide (positive control).
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Vol. 104 • No. 2