Silencing the Odorant Binding Protein RferOBP1768 Reduces the Strong Preference of Palm Weevil for the Major Aggregation Pheromone Compound Ferrugineol

Abstract

In insects, perception of the environment—food, mates, and prey—is mainly guided by chemical signals. The dynamic process of signal perception involves transport to odorant receptors (ORs) by soluble secretory proteins, odorant binding proteins (OBPs), which form the first stage in the process of olfactory recognition and are analogous to lipocalin family proteins in vertebrates. Although OBPs involved in the transport of pheromones to ORs have been functionally identified in insects, there is to date no report for Coleoptera. Furthermore, there is a lack of information on olfactory perception and the molecular mechanism by which OBPs participate in the transport of aggregation pheromones. We focus on the red palm weevil (RPW) Rhynchophorus ferrugineus, the most devastating quarantine pest of palm trees worldwide. In this work, we constructed libraries of all OBPs and selected antenna-specific and highly expressed OBPs for silencing through RNA interference. Aggregation pheromone compounds, 4-methyl-5-nonanol (ferrugineol) and 4-methyl-5-nonanone (ferruginone), and a kairomone, ethyl acetate, were then sequentially presented to individual RPWs. The results showed that antenna-specific RferOBP1768 aids in the capture and transport of ferrugineol to ORs. Silencing of RferOBP1768, which is responsible for pheromone binding, significantly disrupted pheromone communication. Study of odorant perception in palm weevil is important because the availability of literature regarding the nature and role of olfactory signaling in this insect may reveal likely candidates representative of animal olfaction and, more generally, of molecular recognition. Knowledge of OBPs recognizing the specific pheromone ferrugineol will allow for designing biosensors for the detection of this key compound in weevil monitoring in date palm fields.

The genome of pest Rhynchophorus ferrugineus reveals gene families important at the plant-beetle interface

“…The red palm weevil is an invasive species and similar to other insects, it relies mostly on its olfactory system for food foraging and for mating. It uses resistance mechanisms for detoxification of plant secondary metabolites and xenobiotic 33 . We highlight some gene families that are expanded in this context.…”

“…Olfactory gene families are involved in pheromone and odorant detection. They allow R. ferrugineus to locate infected palm trees that emit volatiles in the air, as well as the male aggregate pheromone released to coordinate explosive attacks 33 . The R. ferrugineus genome contains 46 OBP:PBP odorant/pheromone binding proteins (PF01395) and 80 ORs (PF02949).…”

Red palm weevil (Rhynchophorus ferrugineus Olivier): Recent advances

“…Indeed, the very procedure of identification of pheromones such as 4-methyl-5-nonanol, the pheromone of R. ferrugineus, involves electroantennal detection in which the antennae are exposed to the effluent of a gas chromatograph and exhibit a specific response to the effluent when the pheromone is eluted. Recently, Antony et al (2016Antony et al ( , 2018 provided clear genetic evidence for the molecular basis of detection of the pheromone of R. ferrugineus by its antennae. As our first experiment showed (Figure 2), the present results provide field evidence that the mirrors in the "Internal Emission Chamber" may be removed without impairing the functioning of the Electrap.™.…”

“…According to the manufacturer vibrational radiation is emitted from the chamber which then is detected by the insect that is, in turn, attracted to the source of the radiation within the trap (Al-Saroj et al, 2017;Burr, 2002). Although the vibrational radiation theory has been disproven by overwhelming evidence of molecular interaction in insect olfaction (Antony et al, 2016(Antony et al, , 2018Block et al, 2015;Vosshall, 2015), Electrap™ was equivalent in capture to the standard side entry bucket trap used in area-wide Saudi Arabia for mass trapping R. ferrugineus and to a pheromone, kairomone and food baited Picusan™ trap (Al-Saroj et al, 2017;Dhouibi et al, 2017).…”

Expression profiling, phylogenetic, and structural analyses of a laccase gene from the red palm weevil, Rhynchophorus ferrugineus

“…Looking for possible alternative control methods, thus, synthetic biology approaches were proposed. Such as disruption of pheromone communication machinery that interrupts the weevil's olfaction to find host and mate, and finally interrupting its reproduction leading to population decline (Antony et al, 2016(Antony et al, , 2018Soffan et al, 2016). Additionally, cuticular proteins such as laccases and others also proposed as important targets for disruption since they function in cuticle hardening to protect insects from environmental stress and mechanical damage.…”