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Pheromones for conservation

Odour-based methods for monitoring threatened saproxylic insects

The research program aims to integrate chemical ecology research into conservation biology, using saproxylic insects as focal group. Insects living on dead or dying deciduous trees represent a diverse assemblage, which is today threatened all over Europe due to habitat loss and fragmentation. There is thus a serious need for reliable data on present occupancy of these species to select areas with the highest conservation value, but the currently available monitoring methods are both labour-intensive and time-consuming.

Just like other insects, saproxylic beetles and moths rely heavily on olfactory cues during both habitat and mate search. Identifying behaviour-modifying odours and develop odour-based trapping methods may thus facilitate monitoring and improve conservation of these insects.

The research program is focused on three model systems:

  1. The scarab beetle Osmoderma eremita Scopoli, and its larval predator, the click beetle Elater ferrugineus L. living in wood mould in old deciduous trees.
  2. The beetles Harminius undulatus, Peltis grossa, and Upis ceramboide, and their vulnerability to modern forestry management.
  3. Threatened saproxylic species of the moth families Tineidae and Sesiidae.

The hermit beetle Osmoderma eremita lives exclusively inside hollow deciduous trees. It is dependent on large amounts of wood mould, i.e. rotten, loose wood mixed with insect fragments, fungi, and old bird nests. It is today threatened throughout its range in Europe because its habitat has become increasingly fragmented in the modern agricultural landscape. Due to its status as indicator species of the diverse insect fauna associated with hollow trees, it has high conservation priority according to the European Union's Habitat Directive.

The hermit beetle is known for its fruity plum-like scent, which can be perceived by the human nose at distances of tens of meters. We have identified this odour as (R)-(+)-γ-decalactone, and shown that it is released exclusively by males and functions as a sex pheromone for attraction of conspecific females. The odour is emitted in large amounts and can be detected inside hollow trees with traditional headspace sampling techniques.

We have shown that O. eremita beetles are equipped with olfactory receptor neurones (ORNs) that are specific to the (R)-enantiomer of γ-decalactone, and they lack ORNs for detection of the opposite enantiomer. As the racemic mixture of this compound is much cheaper to purchase compared to the pure (R)-enantiomer, the blend can be used for cost-effective monitoring of this species.

We are also using radio telemetry to track movements of O. eremita females to study their dispersal capacity, and how vulnerable they are to habitat fragmentation. A miniature tag is attached to a beetle that has been captured in a pheromone trap, i.e., is dispersing, and its subsequent movements are recorded. Using mark-release-recapture data and radio telemetry, and pheromone-baited traps suspended from oak branches to capture beetles during their dispersal, we hope to get more robust estimates on dispersal distances and population sizes of this threatened species.

An old oak
An old oak, the habitat for many threatened saproxylic beetles, with Lindgren funnel traps for non-destructive trapping. Photo: Glenn Svensson.

Chemical communication in the larval predator Elater ferrugineus

The larvae of the threatened click beetle Elater ferrugineus prey upon larvae of other saproxylic beetles, including Osmoderma eremita. We have shown that females of this predator eavesdrop on the sexual communication of their prey, and use (R)-(+)-γ-decalactone as a kairomone to facilitate location of O. eremita habitats.

Odour traps are much more efficient than pitfall traps in capturing female E. ferrugineus. In fact, the number captured in odour-baited traps during the field season 2006 almost equalled the total number of specimens (147) documented in Swedish collections until 1993.

A female-produced sex pheromone in E. ferrugineushas now been identified, which is highly attractive to male beetles. Thus, two complementory odour systems are now available to monitor this rare species.

Below is a film clip about how to use pheromones for other purpose than fighting pest insects (the film is in Swedish).

More films about research at Lund University

Recent publications

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Hermit beetle
Hermit beetle, Osmoderma eremita. Photo: Glenn Svensson.

People involved

Hermit beetle with radio tag
A female Hermit beetle, Osmoderma eremita with radio tag. Photo: Glenn Svensson.

Collaborators

Click beetle
The click beetle Elater ferrugineus. Photo: Glenn Svensson.