Environmentally regulated abiotic release of volatile pheromones from the sugar-based oral secretions of caribflies

Abstract

We report an abiotic mechanism for the emission of volatile insect pheromones that is controlled by environmentally induced change in the physicochemical properties of the sugar-based release matrix. Male Anastrepha suspensa (Loew) (caribflies) mark mating sites on leaf surfaces by depositing oral secretions that contain sugar, as well as, g-hydroxy acid and g-lactone forms of the diastereomeric aggregation pheromones, epianastrephin and anastrephin. The g-hydroxy acids extend emission over many days via aqueous equilibrium with the thermodynamically less preferred, but more volatile, g-lactones (Â100:1). A kinetic model, which supports a g-lactone diffusion-limited rate, was generated and tested by measuring the effect of temperature and humidity under fixed and ambient atmospheric inputs, respectively. Results show that pheromone release from the markings occurs with a periodicity that parallels relative humidity and complements the daily pattern of the caribflies' reproductive and aggregative activity. This study provides an example of a physicochemical-based inter-organism communication strategy that has been mechanistically linked to the abiotic environmental processing of volatile chemical signals. The exploitation of this natural connectivity will spur environmentally sustainable chemistries, particularly pheromone-based alternatives to insecticide application.

Estimation of climatic favourable areas for locust outbreaks in Spain: integrating species' presence records and spatial information on outbreaks

“…Previous studies have developed models for integrated pest management using pheromones in atmospheric surface layers, incorporating the effects of wind, temperature and humidity (Bisignanesi and Borgas ; Walse et al. ). Thus, for locust pest prevention, further research on models of pheromone efficiency as a function of climatic factors and their geographical projections would be informative.…”

OUP accepted manuscript

“…Our TEM results failed to show any structural connection between the salivary glands and the crop duct or crop lobes. These findings lead us to question the reports of Lu and Teal (2001) and Walse et al (2008) that there is a direct exchange of pheromone components from the salivary glands into the crop lumen in the species studied. Rather, we propose that the components present in the salivary glands, and those within the crop lumen and/or its regurgitated droplet, are first produced in the salivary gland, then deposited onto a surface, and then reingested and deposited in the crop.…”

“…Research emphasis was originally given to the dorsal esophageal bulb or dorsal diverticulum (Ratner and Stoffolano 1982, Estes et al 2009) because of its importance in housing essential symbiotic bacteria that are often passed onto the host fruit during oviposition (Solferini 1990, Mazzon et al 2011, Ben-Yosef et al 2015, Ventura et al 2018). Research was also directed at learning more about the involvement of the crop in producing sexual pheromones used as lekking markers in some species (Nation 1974, 1981; Sivinski et al 1994; Walse et al 2008). The process of bubbling or regurgitation was also studied from a morphological perspective, invariably finding that the crop was implicated as the organ from which the regurgitant, or bubble, was produced (Hendrichs et al 1992).…”

The use of the lactone motif in chemical communication

“…188 The latter lactones occur as an almost racemic 55 : 45 (À)/(+) mixture in A. suspensa. 189 The initial stereochemical assignment has been revised by resolution. 190 The anastrephin lactones have been repeatedly synthesised in racemic 191,192 and optically active forms.…”

“…21), explaining the long activity of these droplets. 189,198 In essence, sugar rich oral secretion droplets are a slow-release formulation for the pheromone. Suspensolide rearranges to the cation 156 which is trapped by water to form acid 167.…”