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

28
Laboratory results
Several alkaloids from native ladybird species: adaline, calvine, precoccinelline, propyleine
(Figure 1), were unambiguously detected in fourth instar larvae of H. axyridis that had
ingested one first instar larva of Adalia bipunctata (L.), Adalia decempunctata (L.), Calvia
quatuordecimguttata (L.), Coccinella septempunctata L. or Propylea quatuordecimpunctata
(L.), respectively.
Adaline Calvine Precoccinelline Propyleine
Figure 1. Various alkaloids detected in H. axyridis according to the coccinellid prey
consumed.
The alkaloid quantity of a single first instar larva, as a prey, is the smallest amount of
exogenous alkaloid that can be fed and detected in H. axyridis; it is inferior to that of a single
egg (Figure 2). The method is sensitive enough to detect all instars. In addition, when the
predator larva has had a contact with a prey but without biting, the quantity of alkaloid
detected is significantly lower (4000x) than when consumption has occurred (Figure 3). The
risk of false positives is thus very limited. After feeding, the exogenous alkaloid concentration
in the predator decreases over time. However, when a first instar A. bipunctata larva was
consumed by fourth instar H. axyridis larvae, the alkaloid was detected in the predator larvae
during 96 h; traces were still detected later on, when the fourth instar H. axyridis larvae had
become pupae and adults. Alkaloid traces were found in the exuviae as well (Figure 4).
Adaline (µg) ± S.E.
2.5
2
1.5
1
0.5
0
egg 1st instar larva
(n=5)
t 6= -3.13; p= 0.020
Figure 2. Adaline in H. axyridis larvae after consumption of one A. bipunctata egg or one 1st
instar larva.
(n=10)