Role of plant volatiles and hetero-specific pheromone components in the wind tunnel response of male Grapholita molesta (Lepidoptera: Tortricidae) to modified sex pheromone blends

Different Binding Affinities of Three General Odorant-Binding Proteins in Grapholita funebrana (Treitscheke) (Lepidoptera: Tortricidae) to Sex Pheromones, Host Plant Volatiles, and Insecticides

Insect general odorant-binding proteins (GOBPs) play irreplaceable roles in filtering, binding, and transporting host odorants to olfactory receptors. Grapholita funebrana (Treitscheke) (Lepidoptera: Tortricidae), an economically important pest of fruit crops, uses fruit volatiles as cues to locate host plants. However, the functions of GOBPs in G. funebrana are still unknown. Three GOBP genes, namely, GfunGOBP1, GfunGOBP2, and GfunGOBP3, were cloned, and their expression profiles in different tissues were detected by the method of real-time quantitative PCR (RT-qPCR). The binding properties of recombinant GfunGOBPs (rGfunGOBPs) to various ligands were investigated via fluorescence binding assays. The three GfunGOBPs were mainly expressed in the antennae of both male and female moths. All these three rGfunGOBPs could bind to sex pheromones, while having varying affinities toward these pheromones. The three rGfunGOBPs also displayed a wide range of ligand-binding spectrums with tested host odorants. The rGfunGOBP1, rGfunGOBP2, and rGfunGOBP3 bound to 34, 33, and 30 out of the 41 tested odorants, respectively. Three rGfunGOBPs had overlapping binding activities to β-myrcene, (-)-α-phellandrene, and ethyl isovalerate with the Ki less than 3.0 μM. The rGfunGOBP1 and rGfunGOBP3 could selectively bind to several insecticides, whereas rGfunGOBP2 could not. Three rGfunGOBPs had the dual functions of selectively binding to sex pheromones and host odorants. Moreover, the rGfunGOBP1 and rGfunGOBP3 can also serve as 'signal proteins' and bind to different insecticides. This study contributed to elucidating the potential molecular mechanism of the olfaction for G. funebrana, and thereby promotes the development of effective botanical attractants or pheromone synergists to control G. funebrana.

Comparison of Sex Pheromone and Kairomone-Enhanced Pheromone Lures for Monitoring Oriental Fruit Moth (Lepidoptera: Tortricidae) in Mating Disruption and Non-Disruption Tree Fruit Orchards

Oriental fruit moth, Grapholita molesta (Busck), populations were monitored using standard sex pheromone lures (OFM L2) and kairomone-enhanced lures to aid the interpretation of trap captures with enhanced relative to conventional lures. Initially, comparison of 10 different lures showed that a10X load of OFM pheromone, codlemone, terpinyl acetate, and acetic acid were key components of the most attractive lures (TRE11034 and 1123). Subsequent trapping studies in mating disruption and non-disrupted orchards in the United States and Spain compared trap captures with TRE1123 and OFM L2 lures. Compared to the OFM L2 lure, the TRE1123 lure captured more moths in mating disruption and non-disrupted orchards, caught female moths, improved the precision of mean population estimates, and led to greater resolution of generational flights. Suppression of trap captures in mating disruption versus non-disrupted orchards was similar with both lures. There were significant linear correlations between weekly trap captures with the two lures in the majority of mating disruption and non-disrupted orchards across locations and years. Furthermore, regression of the slopes of trap capture regressions (i.e., attractiveness of enhanced lures relative to sex pheromone lures alone) versus moth density (as measured by mean cumulative moth capture with TRE1123 and OFM L2 lures) exhibited a significant positive relationship in non-disrupted orchards, indicating enhanced lures were relatively more attractive under high population densities. This relationship was not significant in mating disruption orchards, likely due to the density independent, non-competitive mechanism of mating disruption for oriental fruit moth when using high-dose reservoir dispensers.

Extremely low neonicotinoid doses alter navigation of pest insects along pheromone plumes

The prevailing use of neonicotinoids in pest control has adverse effects on non-target organisms, like honeybees. However, relatively few studies have explored the effect of sublethal neonicotinoid levels on olfactory responses of pest insects, and thus their potential impact on semiochemical surveillance and control methods, such as monitoring or mating disruption. We recently reported that sublethal doses of the neonicotinoid thiacloprid (TIA) had dramatic effects on sex pheromone release in three tortricid moth species. We present now effects of TIA on pheromone detection and, for the first time, navigational responses of pest insects to pheromone sources. TIA delayed and reduced the percentage of males responding in the wind tunnel without analogous alteration of electrophysiological antennal responses. During navigation along an odor plume, treated males exhibited markedly slower flights and, in general, described narrower flight tracks, with an increased susceptibility to wind-induced drift. All these effects increased in a dose-dependent manner starting at LC0.001 - which would kill just 10 out of 106 individuals - and revealed an especially pronounced sensitivity in one of the species, Grapholita molesta. Our results suggest that minimal neonicotinoid quantities alter chemical communication, and thus could affect the efficacy of semiochemical pest management methods.

Structural Insights into Two Representative Conformations of the Complex Formed by Grapholita molesta (Busck) Pheromone Binding Protein 2 and Z-8-Dodecenyl Acetate

Grapholita molesta is a notorious fruit borer globally, causing severe damage to fruit production. To control the pest, one commonly used mean is pheromone-mediated management. As an important sex pheromone, Z-8-dodecenyl acetate (Z8-12: Ac), is often coformulated with other active ingredients to regulate the behavior of G. molesta. To uncover its interactions with G. molesta pheromone binding protein 2 (GmolPBP2) is used to help develop insect attractants. During 200 ns molecular dynamics simulations, two representative conformations of the GmolPBP2-Z8-12: Ac complex are selected. Conformation II at the time of 14-106 ns is dominantly maintained by the hydrophobic interactions and hydrogen bond. In Conformation I, which lasts from 106 to 200 ns, the hydrophobic interactions are enhanced while the hydrogen bond is quite weakened, due to the formation of a more sophisticated hydrophobic binding pocket and the enlargement of hydrogen bond distance. Taking the two conformations as a whole, the affinity between GmolPBP2 and Z8-12: Ac is crucially determined by three hot-spots including Phe11, Trp36, and Ile51. These results would provide a basis for the discovery, optimization, and design of leading compounds potentially active to attract G. molesta.