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Forschung

© Universität Bielefeld

Forschung

The current research of the Biological Collection focuses on the chemical defense mechanisms of insects, especially of stick and leaf insects (Phasmatodea).

These insects are well known for their astonishing ability to imitate twigs, leaves or bark. In addition to this and other defensive strategies, many phasmatodean species use prothoracic repellent glands to spray defensive chemicals when disturbed by predators or parasites. These glands are considered as a derived autapomorphic trait of the Phasmatodea and are widely distributed among these insects.

Figure 1: Phenotypical diversity and defensive strategies of stick and leaf insects: A: Stick masquerade in Sigaruphasma bouladoui (Cladomorphinae, Dominican Republic). B: Leaf masquerade in Cryptophyllium sp. (Phylliidae, China). C: Cryptic coloration and thorns in Brockphasma spinifemoralis (Necrosciinae, Vietnam). D: Cryptic coloration in Onchestus rentzi (Lanceocercata, North-East Australia). E: Aposematic coloration in Oreophoetes peruana (Diapheromerinae, Peru). F: Startle Display with red hind wings in Diapherodes jamaicensis (Cladomorphinae, Jamaica).

We investigate the (functional) anatomy and the chemical substances by use of µCT scans, histology, electron microscopy and gas chromatography combined with mass spectrometry. The size of the glands varies considerably among the species. For instance, in Carausius morosus, they are remarkably small, measuring just 0.5 mm in length. In contrast, the glands in species such as Anarchodes annulipes reach lengths of nearly 13 mm. The chemical components of the repellent secretion are also unexpectedly diverse. To date, at least 31 different substances have been identified in 27 phasmatodean species. The majority of species produces monoterpenes, but also other substances such as heteroaromatics, spiroketals and pyrazines were found in different taxa.

Our research provides coherent surveys of the phasmatodean defensive glands that combine anatomy and chemistry in comparative approaches across all major lineages of this group of insects, aiming to uncover the anatomical and chemical diversity of this elaborate defensive system.

Figure 2: Histological section of repellent glands in Lamachodes sp. (Necrosciinae, Vietnam). A: Cross section with repellent glands (rg) and digestive system (ds). B: Enlarged image of one repellent gland from A. cu = cuticle, gc = glandular cell, ge = glandular epithelium, mu = musculature. Scale bars: 0.5 mm (A), 0.2 mm (B). Histological sections were made according to Beckers et al., 2022.
Figure 3: Prothoracic repellent glands of stick and leaf insects. A: Dorsal view on the repellent glands in situ (arrowheads) of a female Lamachodes sp. (Necrosciinae, Vietnam), tergal plates removed. B: Repellent gland opening (arrowhead) of a male Spinohirasea bengalensis (Necrosciinae, Vietnam). C: Male (left) and female Anisomorpha paromalus (Pseudophasmatidae, Mexico) emitting the repellent secretion against the attacker.
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