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Elm leaf beetle, Xanthogaleruca luteola Müller (Col.: Chrysomelidae) a pest of ornamental elms. Thyme, Thymus vulgaris (Lamiaceae) is an important medicinal. In this study, effect of Thymus vulgaris L. essential oil was tested on X. luteola in laboratory. The LC 30 and LC 50 values were estimated by leaf dipping method to third instar larvae (LC30 =2.065 and LC50 =4.237% W/V). The feeding efficiency was significantly reduced in treated larvae except the approximate digestibility (94.82 in control and 98.23 in treatment). The treated larvae showed a significant reduction key biochemicals. Reduced glucose and uric acid but increased protein level was seen. Severe reduction in ovarian texture both morphologically and histologically was observed which depicts a prolonged effect of the used EO on survivors. We believe that the thyme EO has the potential to be formulated for smaller scale trial to meet the needs of an environmental friendly compound.

The effect of monoterpenoid 1,8-cineol on the toxicity and physiology of elm leaf beetle, Xanthogaleruca luteola Müller under laboratory conditions (26 ± 1°C, 65 ± 10% RH and 16L : 8D h) was investigated. Initially, LC30 and LC50 values of the constituent were estimated to be 23.5 ppm and 31.9 ppm for the last instar larvae after 48 h, respectively. Significant changes were observed in the values of relative growth rate (RGR), efficiency of conversion of ingested food (ECI), efficiency of conversion of digested food (ECD), approximate digestibility (AD) and consumption index (CI) between control and treated larvae with 1,8-cineol. The amounts of protein, glucose and urea decreased in the treated larvae in comparison with control. Similar findings were observed in the activities of alkaline phosphatase and lactate dehydrogenase while the activities of glutathione S-transferase and esterase significantly increased in the treated larvae using CDNB and α-naphtyl acetates as the substrates. Morphological and histological changes brought about by 1,8-cineol in the present study are indicative of growth inhibition targeting specific organs such as those of reproduction. We believe that 1,8-cineol can be considered as a safe and environmentally friendly compound.