Inhibitory effect of thymol on pheromone-mediated attraction in two pest moth species.

Plant essential oils are considered as important bio-sources for the development of natural and environmentally safe pest control tools due to their multiple modes of action on insects. In this paper we have evaluated the activity of commercially available thyme oil and its constituents thymol, carvacrol, and p-cymene, as potential disruptants of the pheromone-mediated communication in the major pest moths Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae), and Grapholita molesta (Busck) (Lepidoptera: Tortricidae). In electroantennographic assays, the antennal response of males to thyme oil, thymol, and carvacrol was altered at high doses (103-104 µg), shifting the signal waveform into a biphasic negative-positive potential that caused a decay in the response. In wind tunnel assays, pheromone-mediated attraction of males of both species was interrupted in presence of thyme oil. Further trials demonstrated that thymol alone reduced the number of G. molesta and S. littoralis males landing on the pheromone source. This effect did not differ from that of thyme oil, although the latter provoked a significant reduction on downwind behavior steps in S. littoralis. Overall, our findings provide a preliminary basis for delving into the effect of thyme oil, and especially of its major constituent thymol, as potential mating disruptants of both species.

Influence of Age, Host Plant and Mating Status in Pheromone Production and New Insights on Perception Plasticity in Tuta Absoluta.

The tomato leafminer Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) is one of the most important pests of tomato worldwide. However, in spite of its tremendous economic importance, the success of environmentally friendly measures to control the pest is still limited. Study of physiological and behavioral parameters that affect pheromone production has provided useful information for pest management. Our results show no clear difference in pheromone production by females over the period from 2 h before to 2 h after the scotophase. However, pheromone production was clearly dependent on female age, with young females producing the highest amount of each pheromone component 10 days after emergence. In the presence of the host plant (physical contact and olfaction of the plant volatiles), virgin and mated females produced higher amounts of the major component of the pheromone (TDTA) than those in the absence of plant and those devoid of olfaction (antennectomized) but in physical contact with the plant. In electrophysiological experiments, TDTA elicited slightly lower responses on male antennae than the pheromone mixture. When stimulated at certain time intervals after the first exposure to TDTA, male antennae became more sensitive to the stimulus (sensitization effect). For the first time in an insect of the family Gelechiidae, we have found that females are able to detect their own pheromone (autodetection). Altogether, our results may represent a step forward in the knowledge of the chemical communication of this important pest.

Enantioselective Synthesis and Activity of All Diastereoisomers of ( E)-Phytal, a Pheromone Component of the Moroccan Locust, Dociostaurus maroccanus.

The Moroccan locust, Dociostaurus maroccanus (Thunberg, 1815) (Orthoptera: Acrididae), is a polyphagous pest capable of inflicting large losses in agriculture under favorable environmental and climatic conditions. Currently, control of the pest relies solely on the application of conventional insecticides that have negative effects on the environment and human safety. In the search for a more rational, environmentally acceptable approach for locust control, we have previously reported that ( Z/ E)-phytal (1) is a male-produced candidate sex pheromone of this acridid. This molecule, with two stereogenic centers at C-7 and C-11, has four different diastereomers along with the Z/ E stereochemistry of the double bond at C-2. In this paper, we present for the first time the enantioselective synthesis of the four diastereomers of ( E)-phytal and their electrophysiological and behavioral activity on males and females. Our results demonstrate that the ( R, R)-phytal is the most active diastereomer in both assays, significantly attracting females in a double-choice Y olfactometer, and confirming the previous chromatographic assignment as component of the sex pheromone of the Moroccan locust.

Synthesis, Functional Assays, Electrophysiological Activity, and Field Tests of Pheromone Antagonists of the Tomato Leafminer, Tuta absoluta.

The tomato leafminer, Tuta absoluta, is one of the major pests of tomato and other Solanaceae in many regions worldwide. In the search for new strategies to control this pest, we present herewith the stereoselective synthesis, electrophysiological activity, functional analysis, and field tests of new chemicals as possible antagonists of the sex pheromone of the leafminer. The chemicals are methyl ketone (MK) and trifluoromethyl ketone (TFMK) structural analogues of both components of the pheromone. Most of the chemicals exerted per se some electrophysiological activity and inhibited the electroantennographic response to the pheromone when vapors of the inhibitor were passed over the antennae. Except TFMK 3, which elicited a modest effect, the compounds did not exhibit antiesterase activity on the pheromone-degrading enzymes of the antennae, but in the field the chemicals, particularly MK 5, notably decreased the number of catches when mixed with the pheromone in 1:1 and 10:1 ratios, regardless the infestation level of the plot. These results suggest that MK 5 is a good behavioral antagonist of the pheromone to be considered as a putative agent to control the pest in new future integrated pest management (IPM) strategies.