Treehoppers (Membracidae, Aetalionidae, and Melizoderidae)
are the nearest known relatives of leafhoppers (Cicadellidae). Traditionally,
the treehopper lineage has been considered to be a sister group to Cicadellidae.
However, recent molecular data suggest that treehoppers have derived
from within Cicadellidae (Dietrich et al. 2001). Go to C. H. Dietrich's treehopper site...
The integument of treehoppers has no brochosome
coat. Several authors have reported finding brochosomes on the integument
(Day 1993) or in the Malpighian tubules (Gouranton & Maillet 1967)
of certain Membracidae, but in neither case the evidence is substantial.
More extensive studies of the treehopper integument (Dietrich 1989) and
the Malpighian tubules (Rakitov unpublished) indicated that treehoppers
do not produce brochosomes. However, the structure of the Malpighian tubules
in Membracidae is almost identical to that in leafhoppers, comprising well
developed secretory segments. In both
immatures and adults, the cells of these segments synthesize and export
products distinct from brochosomes (like in certain leafhopper nymphs,
which produce secretory products other than
brochosomes). Also like leafhoppers, Membracidae display post-molt
anointing behaviors, releasing
the Malpighian tubule secretory products and spreading them over the new
integument (Rakitov, 1996). These behaviors have been observed so far only
in a few species from the tribes Centrotini, Heteronotini, and Platycotini.
It remains unknown whether they are characteristic of all membracids. Neither
the Malpighian tubules, nor post-molt behaviors have been studied in Aetalionidae
Anointing behavior in adults of Gargara genistae (F.)
(above) and Platycotis vittata (F.) (right).
Treehopper nymphs release
the Malpighian tubule secretion onto the plant surface and bathe in it
. This behavior is identical to the bathing
anointing behavior of certain leafhopper nymphs.
Above: anointing behavior in a nymph of Gargara genistae
(F.) (secretory fluid is shown with white arrows).
The function of anointing behaviors in Membracidae remains
completely unknown. The Malpighian tubule secretory products of treehoppers
do not form any particulate layer on the integument and apparently do not
make it water-repellent. Their chemical nature and properties have not
been investigated. The leg chaetotaxy in treehoppers is reduced, which
correlates with lack of the brochosome coat. According to a recent estimate
of the phylogeny, treehoppers must have lost the ability to produce
brochosomes secondarily (Dietrich et al. 2001). The ecological conditions
which might have favored these changes in the treehopper lineage remain
obscure. More extensive studies of the behaviors and the Malpighian tubule
secretions in all treehopper families (Membracidae, Aetalionidae, and Melizoderidae)
are needed to clarify the biological function and evolution of the Malpighian
tubule secretions in this lineage.