8. Treehoppers
 
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 More extensive studies of the treehopper integument (Dietrich 1989) and the Malpighian tubules (Rakitov unpublished) indicated that treehoppers do not produce brochosomes.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 and Melizoderidae.

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).
Research problems
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.
More about evolution...

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