Antennal sensory organs and glands of the harlequin ladybird, Harmonia axyridis

Abstract

Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is a sub-cosmopolitan species. Native to Asia, it has been released during the 20th century for classical and augmentative biological control of several herbivorous insects, mostly aphids and coccids. Despite its recognized positive impact on biological control, H. axyridis is now considered among the most dangerous invasive species in Europe and in most places where it has established. This is mostly due to its ability to reduce the populations of native predatory species of the same trophic guild. When exploring a new area, H. axyridis adults use semiochemical cues to acquire information about the habitat. Presumably, these cues are perceived by the sensilla located on the antennae. Surprisingly, in spite of the huge literature existing on H. axyridis, the antennal sensory organs have been poorly characterized. Here, we used scanning and transmission electron microscopy (SEM, TEM) techniques to study H. axyridis antennae, with focus on the various types of sensilla and their distribution in male and female individuals. The presence of various classes of antennal sensilla belonging to the main types described in insects (chemoreceptors, mechanoreceptors, and thermo-hygroreceptors) was highlighted, as well as the widespread presence of antennal glands. The investigations showed some peculiar characteristics not known in Coccinellidae, such as the concentration of sensory structures at the level of the distal part of the apical antennomere and the discovery of antennal glands associated with it. No sexual dimorphism was revealed, neither for the general structure of the antenna (similar number of antennomeres and presence of modifications), nor for the total length and width of the antenna, the relative size of the antennomeres, the types of antennal sensilla, of their distribution and abundance. The potential relevance of these sensory structures and antennal glands, reported for the first time in Coccinellidae, is discussed in the context of intra-and interspecific communication.

Antennal Transcriptome Analysis and Identification of Candidate Chemosensory Genes of the Harlequin Ladybird Beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)

“…Most chemosensory genes did not exhibit sex-specific nor sex-biased expression. This is consistent with recent description of antennal morphology that did not reveal relevant sexual dimorphism in H. axyridis , neither for the antennal general structure, nor for the types of sensilla and their abundance [ 33 ]. However, this does not preclude that the significance of the perceived odors may differ between males or females.…”

“…Behavioural and electrophysiological experiments demonstrated that H. axyridis responds to volatile semiochemicals [ 1 , 31 , 32 ]. Additionally, various types of antennal chemoreceptor sensilla (notably basiconica, chaetica, and grooved peg) have been recently characterized [ 33 ]. Therefore, understanding the molecular basis of H. axyridis chemosensory reception, in particular olfaction, is likely to provide new information to increase the efficacy of this predator in biological control or to reduce its populations in those areas where H. axyridis has become a concern for local biodiversity [ 34 ].…”

Antennal transcriptome analysis and identification of candidate chemosensory genes of the harlequin ladybird beetle,Harmonia axyridis(Pallas) (Coleoptera: Coccinellidae)

“…Although it is thought that ladybird maxillary palps are the most adequate structures for the perception of nonvolatile molecules [100], our results suggest a possible role of antennal contact in sugar detection. Possibly, the long sensilla chaetica that are positioned in H. axyridis at the tip of the antenna may be involved in the perception of such nonvolatile molecules [33]. Our analysis also revealed the presence of candidate receptors for CO 2 in H. axyridis antennae.…”

“…Sensilla basiconica are responsible for carbon dioxide detection in D. melanogaster [12]. These sensilla are present and abundant in male and female H. axyridis antennae [33]. Although this kind of sensilla is known to be involved in the detection of a plethora of molecules in insects, including volatile molecules, it is possible that CO 2 detection is mediated by such sensilla in H. axyridis .…”

Entomophagous insects – an introduction

“…The chemical ecology of entomophagous insects is addressed focusing both on the functional morphology of antennal sensilla and on the exploitation of semiochemicals to improve predator efficacy. Sevarika et al (2021) investigated the antennal sensilla of Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) using scanning and transmission electron microscopy. Various types of sensilla (chemoreceptors, mechanoreceptors, and thermo‐hygroreceptors) and their distributions are described.…”