Data sheet lily leaf beetle
Latin name:
Galerucella nymphaeae (Linnaeus, 1758)
Distribution:
Europe and North America
Size (in cm:
5.2 to 6.5mm
age expectation:
1 year
behavior/stocking
Occurrence in the pond:
pest on water lilies
Dangerous?
Harmless to humans Andreas Rusch, Galerucella nymphaeae 1, CC BY-SA 3.0
key data
The lily leaf beetle Galerucella nymphaeae As a member of the leaf beetle family (Chrysomelidae), it belongs to a group with over 50,000 described species. All species are pure herbivores. The adult leaf beetles and their larvae feed on all parts of plant tissue.
The water lily leaf beetle can be found on the eponymous host plants in the pond. The infested floating leaves of the water lilies then show clearly visible signs of feeding which, due to their characteristic shape, point to the water lily leaf beetle.
Typical characteristics
imago
The imago of the lily leaf beetle is 5.2 to 6.5 mm long. The U-shaped thorax seen from above is colored dark brown. The distal part of the elytra contrasts with an ocher border. The head and legs are also ocher.
The center of the elytra is occupied by a bare and shiny, almost triangular area. The middle hips are separated and do not touch.
larva
The anthracite-colored larvae have a slightly flattened, almost cylindrical body that is largest in the head area. The larvae are about 3 mm long after hatching.
confusion
The water lily leaf beetle can be confused visually with two similar species. These are the swamp leaf beetle Galerucella aquatica and the swamp leaf beetle Galerucella sagittariae. In the wild, reliable differentiation in living objects is only possible by identifying the different host plants.
Occurrence and life in the pond
Egg packets, larvae and adult beetles are found on top of the floating leaves of water lilies they infest. The pest infestation occurs from May and is initially noticeable as cockroach damage, later as pitting.
The water lily leaf beetle has no real adaptation to an aquatic lifestyle, although the larva and beetle can survive briefly under water with the help of the air film that forms on the body surface. The body surface of the animals is water-repellent. This effect is supported by a cushion of adhesive hairs (setae) in the imagines.
feed and nutrition
Among the water lilies, the white water lily is often mentioned Nymphaea alba and the yellow water lily Nuphar lutea adopted as a host plant. The surfaces of the floating blades are preferred; other plant components are more rarely affected.
propagation
During the year, the lily leaf beetle develops two generations. Both generations are able to overwinter. In the spring, around April, the square egg packets, which have a diameter of around 2 mm, are laid on the floating leaves of the water lilies that are forming at this time.
From this clutch of about a dozen eggs, the finished beetle develops through the three larval stages of the beetle pupa. This creates the summer generation, which can mate until September. The development process of the spring generation is completed within four to six weeks. The oviposition of the overwintering generations takes place again in the following year.
combat
Larvae and adults of the water lily leaf beetle are not able to swim and drown after a short time if they get below the water level. To protect the water lilies, the water lily leaf beetle can therefore be controlled by simply rinsing or spraying the floating leaves. Infested lily pads that have been harvested should be dug up.
In order to support the resistance of water lilies in culture against the water lily leaf beetle, care must be taken to ensure sufficient fertilization for these heavy feeders. Affected water lilies react to the infestation of the water lily leaf beetle with the increased production of tannins. As a result of this defense reaction, the pond can turn brown and lead to undesirable acidification of the pond.
Leaf beetles in science
Galerucella nymphaeae as an evolutionary model for speciation
The water lily leaf beetle is very specific in its choice of host plants (oligophagy). In addition to the populations that attack water lilies, there are also those that have specialized in other families of pond plants. In addition to pond plants, land plants are also preferred by some populations. Among the cultivated plants, the garden strawberry is particularly important Fragaria × ananassa worth mentioning.
This intraspecific variability in the dietary specialization of the lily leaf beetle can thus be interpreted as a potential for incipient sympatric speciation through different food sources. Against this background, the species status of the North American population, which shows a different polypeptide composition in the eggshell, is under discussion.
Leaf beetles in bionic research
Due to their differently structured adhesive hairs, leaf beetles can stick to different surfaces. The adhesive forces are strongest on the disc-shaped Sedae, but the spoon-shaped and pointed adhesive hairs require far less force when detaching and can therefore be detached from the surface more quickly by the beetle.
The water lily leaf beetle thus forms a model for the technically possible realization of multiple detachable adhesive bonds with different tasks.