Abstract
Simple SummaryParasitic wasps are the major natural enemies of many organisms, and therefore they are broadly used in the biological control of numerous agricultural and horticultural pests. For example, Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is a tiny natural egg parasitoid of various agricultural pest insects, including Plutella xylostella, Helicoverpa armigera, Spodoptera frugiperda and Ectomyelois ceratoniae. However, how T. pretiosum seek and localise host insect eggs is still not clear. The olfactory system is critical in guiding insect behaviours, including mating, feeding and oviposition, which play pivotal roles in the interactions between parasitoid wasps and their hosts. This project aimed to investigate T. pretiosum major olfactory tissue (antennae) and the olfactory genes, including odorant binding proteins (OBPs) and odorant receptors (ORs). T. pretiosum adult antennae were examined under scanning electron microscopy, and four types of olfactory sensilla were observed. Using T. pretiosum genome, 22 OBPs and 105 ORs were identified, which were further compared with olfactory genes of other Hymenoptera insect species. The expression patterns of OBPs between T. pretiosum male and female adults were examined to identify female- or male-specific OBPs. This study enriches our knowledge of T. pretiosum olfactory system and will help better use it in the integrated pest management (IPM) for many insect pest species.Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is a tiny natural egg parasitoid of several agricultural pest insects, which has been widely used in the biological control for Plutella xylostella, Helicoverpa armigera, Spodoptera frugiperda and Ectomyelois ceratoniae. However, limited studies have been conducted on T. pretiosum olfactory system, which is critical in regulating insect behaviours. In this study, T. pretiosum adult antennae were investigated under ascanning electron microscopy (SEM). Four types of olfactory sensilla were observed, including chaetica sensilla (CS), trichoid sensilla (TS), faleate sensilla (FS) and placoid sensilla (PS). Using T. pretiosum genome, 22 putative odorant binding proteins (OBPs) and 105 odorant receptors (ORs) were identified, which were further compared with olfactory genes of Apis mellifera, Nasonia vitripennis and Diachasma alloeum. The expression patterns of OBPs between T. pretiosum male and female adults were examined by quantitative real time PCR (qRT-PCR) approaches. Three female-specific OBPs (TpreOBP19, TpreOBP15 and TpreOBP3) were identified, which may play crucial roles in T. pretiosum host-seeking and oviposition behaviours. This study enriches our knowledge of T. pretiosum olfactory genes and improves our understanding of its olfactory system.
Highlights
Insect behaviours, including mating, foraging, host-finding and oviposition, are guided by their olfactory systems [1]
The flagellum is differentiated into basal anelli, funicle and apical club (C), which are all apparent in the female antenna (Figure 1a,c)
Three types of sensilla were recognised from male adult antennae, and they are chaetica sensilla (CS), trichoid sensilla (TS) and placoid sensilla (PS) (Figure 1e,f)
Summary
Insect behaviours, including mating, foraging, host-finding and oviposition, are guided by their olfactory systems [1]. Hair-like olfactory sensilla distributed over the surface of antennae are utilised by insects to detect chemical signals from the environment [2,3,4]. Various gene families have been reported to play pivotal roles in the dynamics, selectivity and sensitivity of insect olfactory systems, including odorant binding proteins (OBPs) [5], odorant receptors (ORs) [6,7], ionotropic receptors (IRs) [8], sensory neuron membrane proteins (SNMPs) [9] and odorant-degrading enzymes (ODEs) [5,10]. ORs are localised on the dendritic membrane in insect olfactory sensilla, detecting odorant compounds and transducing olfactory signals to insect brains to regulate behaviours [13]. ODEs can degrade the odorant compounds after they activate ORs, which clean the olfactory system for the new cycle of detection [5,10,14]
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