Influence of temperature in action of fumigant natural insecticides

YANINA ROSSI Y SARA M. PALACIOS

Viña del Mar, Chile

Simposio; Biology, Chemistry, Pharmacology and Industrial Applications of Plants of the Americas; 2009

Previously, we have determined the fumigant lethal dose 50 (LC50) of essential oils (EOs) against Musca domestica [1,2] finding that the EO obtained from Eucalyptus cinerea F. Muell. ex Benth. leaves, Mintostachys verticillata (Griseb.) Epling leaves and Citrus sinensis (L.) Osbeck fruit peel, as well as their most abundant terpenes (T), 1,8-cineole, (R)(+)-pulegone and (4R)(+)-limonene, respectively, resulted as good candidates for the control of this insect. As temperature is an important environmental factor influencing the action of fumigants on insects [3], the role of this parameter during fumigation was examined on bioassays conducted for 30 minutes. The temperatures tested were 18°C, 26°C, 30°C and 35°C.LC50 of all EOs, changed with temperature, although in different forms (Fig. 1-4). For instance, LC50 of C. sinensis EO had a minimum (most toxic) at 26 °C and increased values (lower toxicity) at 18, 30 and 35°C (Fig. 1), while the LC50 of E. cinerea (Fig. 2) and M. verticillata EOs (Fig. 3) have a maximum (lower toxicity) at 26 °C incrementing their toxicity at lower and higher temperatures. The LC50 of Ts showed similar tendency compared with that of the corresponding EOs (Fig. 1-3). On the light of these results we can infer that C. sinensis EO have a different mode of action than the E. cinerea and M. verticillata EOs. These differences could be due to the different mode of action of the constituent terpenes or at least of the main component. LC50 of E. cinerea and M. verticillata EOs showed a similar variation with the temperature, in consequence we assayed mixtures of both EOs or their principal T, in order to determine if they act in a additive or synergistic mode of action. Figure 4 shows the variation of LC50 of a mixture of E. cinerea and M. verticillata EO (1/1 w/w) as well as of mixture of (R)(+)-pulegone and 1,8-cineole (1/1 w/w). Both curves showed a sigmoid shape rather the parabolic shape shown by the EOs or Ts alone. From these data we can infer that the mode of action of Ts in houseflies will be a characteristic of each T as well as of the combination of T, consequently the mode of action of an EO, been they mixtures of Ts, will be difficult to predict because as was demonstrated here, a given EO or T can change its action against M. domestica depending if they are alone or combined with other EO or T. [1] Palacios, S.M., Bertoni, A., Rossi, Y., Santander, R., Urzúa, A. ?Efficacy of essential oils from edible plants as insecticides against the house fly, Musca Domestica L.?, Molecules, 14, 1938-1947 (2009). [2] Palacios, S.M., Bertoni, A., Rossi, Y., Santanderand R., Urzúa A. ?Insecticidal activity of essential oils from native medicinal plants of central Argentina against the house fly, Musca domestica (L.)?, Parasitology Research, (2009) in press. [3] Papachristos, D.P., Stamopoulos, D.C. ?Toxicity of vapours of three essential oils to the immature stages of Acanthoscelides obtectus (Say) (Coleoptera: Bruchidae)?, Journal of Stored Products Research, 38, 365?373 (2002).