Oviposition deterrent activity of basil plants and their essentials oils against Tuta absoluta (Lepidoptera: Gelechiidae).

The leafminer Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) is one of the most important pests of tomato, reducing crop yields by up to 100% in greenhouses and fields, in several countries globally. Because synthetic insecticides lead to resistance and have adverse effects on natural enemies and the health of producers, alternative control methods are needed. In this study, we assessed the oviposition-deterring effect of basil plants, Ocimum gratissimum L. and O. basilicum L. (Lamiaceae), using dual-choice behavioural assays performed in flight tunnels. We found that both plants significantly reduced T. absoluta oviposition behaviour on a tomato plant located nearby. To evaluate the potential effect of basil volatile organic compounds, we formulated essential oils of both plant species in paraffin oil, and observed a similar oviposition-deterring effect. Gas chromatography analyses detected 18 constituents in these essential oils which the major constituents included thymol (33.3%), p-cymene (20.4%), γ-terpinene (16.9%), myrcene (3.9%) in O. gratissimum and estragol (73.8%), linalool (8.6%), ß-elemene (2.9%) and E-ß-ocimene (2.6%) in O. basilicum. Twenty and 33 compounds were identified of the volatiles collected on O. gratissimum and O. basilicum plants, respectively. The main components include the following: p-cymene (33.5%), γ-terpinene (23.6%), α-terpinene (7.2%), α-thujene (6.7%) and E-α-bergamotene (38.9%) in O. gratissimum, and methyl eugenol (26.1%), E-ß-ocimene (17.7%), and linalool (9.4%) in O. basilicum. Four compounds (α-pinene, ß-pinene, Myrcene, Limonene) were common in essential oils and plants. Our results suggest the valuable potential of basil and associated essential oils as a component of integrated management strategies against the tomato leafminer.

Structure and distribution of the sensilla on the antennae of Tuta absoluta (Lepidoptera: Gelechiidae).

The tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), is a widespread devastating pest that develops on tomato and other economically important solanaceous crops. Current semiochemically-based management strategies still fail to significantly reduce damages and need to be improved. Here we describe under scanning and transmission electron microscopy the structure and distribution of the sensilla that are displayed on adult antennae. These were similar in size between males (3424.4±135.3µm) and females (3292.1±111.5µm), being segmented into a scape, a pedicel, and a distal filiform flagellum. Eight morphological sensilla types were observed on both sexes: Böhm's bristles, sensilla squamiformia, sensilla trichodea, sensilla basiconica (two subtypes), sensilla chaetica, sensilla coeloconica, sensilla auricillica, and sensilla styloconica. The main sexual dimorphism was related to the higher abundance of sensilla trichodea in males, twice as abundant as in females. The putative functional significance of the different sensilla types regarding the insect ecology is discussed based on the available literature. This work provides descriptions of the antennae and related sensory structures. We expect these results to help develop further electrophysiological investigations aiming to a better understanding of T. absoluta olfaction.