Science Facing Aliens - Invasive Alien Species in Belgium - Belgian ...

Detection of intraguild predation by Harmonia axyridis on native
cocccinellids by alkaloids
Louis HAUTIER 1 , Jean-Claude GRÉGOIRE 2 , Jérôme DE SCHAUWERS 3 , Gilles SAN MARTIN 3,4 ,
Pierre CALLIER 3 , Jean-Pierre JANSEN 1 & Jean-Christophe DE BISEAU 3
1 Département Lutte biologique et Ressources phytogénétiques, Centre wallon de Recherches
agronomiques , Rue de Liroux, 2, B-5030 Gembloux, Belgium
2 Lutte biologique et Ecologie spatiale, Université Libre de Bruxelles, CP 160/12, Av. F.D.
Roosevelt 50 - 1050 Brussels, Belgium
3 Eco-Ethologie évolutive, Université Libre de Bruxelles, CP 160/12, Av. F.D. Roosevelt 50 -
1050 Brussels, Belgium
4 Present address: Écologie comportementale et conservation de la biodiversité , BDIV ,
Université catholique de Louvain, Croix du Sud 4 B-1348 Louvain-la-Neuve, Belgium
Introduction
In laboratory conditions, the invasive ladybird Harmonia axyridis Pallas is well known as an
intraguild predator of ladybird species (Pell et al. 2008, Ware & Majerus 2008) but also of
other aphidophages (Koch 2003). However, the real impact of H. axyridis intraguild predation
(IGP) on native coccinellids is poorly known in natural conditions, where multiple prey
species occur and where prey has the opportunity to escape. To follow predator - prey
interactions, several techniques have been developed (Harwood & Obrycki, 2005): analysis of
food remains by gut dissection (Triltsch, 1999), use of monoclonal antibodies (Hagler, 2006)
and molecular analysis with detection of species-specific DNA sequences (Hoogendoorn &
Heimpel, 2001). Molecular techniques have been used successfully to detect IGP in
coccinellids, however, with some limitations regarding detection time as a result of the rapid
digestion of prey DNA (Gagnon et al., 2005). A new method to monitor IGP of coccinellids
in natural conditions is based on alkaloid detection by gas chromatography - mass
spectrometry (Hautier et al., 2008). As many ladybird species use alkaloids as a chemical
defence (Daloze et al., 1994), these compounds can be used as predation tracers. To apply this
approach, we firstly developed a laboratory alkaloid detection technique for H. axyridis
larvae. Next, the influence of several factors on the detection efficiency was studied under
laboratory conditions: prey instar, risk of false positives and time of detection. Finally, the
method was validated by testing it on H. axyridis larvae sampled in potato fields.
Alkaloid detection
H. axyridis larvae were crushed in 200 µl of methanol and soaked during 10 minutes. The
extracts were subsequently filtered on cotton wool and the filtrate was concentrated under
nitrogen. The residues were dissolved in methanol and an aliquot was analysed by gas
chromatography - mass spectrometry. Analysis conditions are fully described in Hautier et al.
(2008).
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