Close, but not too close: social interactions among mother treehoppers
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Insectes Sociaux
EDITORIAL
Close, but not too close: social interactions among mother treehoppers M. H. Richards1 Published online: 4 September 2020 © International Union for the Study of Social Insects (IUSSI) 2020
Treehoppers (Membracidae, Hemiptera) may be best known for their sometimes bizarre morphology and colouration, but they also exhibit interesting and varied maternal care. Eggs and juveniles are prime targets for predators and parasitoids, whereas adults have effective defenses, and many treehopper species exhibit substantial maternal care. Mothers often lay egg masses in slits that they cut into the underside of a leaf on their favoured host plant, inserting the eggs and then covering them with a secretion from their accessory glands. These simple structures are functionally equivalent to bird nests. In subsocial species, juveniles remain with their mother after hatching, and maternal care can be quite sophisticated. In many species, the pronota of adult females are modified as large shields under which their offspring can hide, and some of the baroque humps, bumps, and other extensions on their backs likely help to fend off aerial predators. Mothers facilitate larval feeding by cutting slits in plant tissues to make it easier for juveniles to suck up plant juices. Mothers even herd their offspring, calling stray juveniles back to the safety of the group (an interesting view of this behaviour: https://www.youtube.com/watch?v=Y0oZk GGIe0I). When juveniles of treehoppers or other insects remain together or with their mother for prolonged periods of time, this sets the evolutionary stage for further social evolution. Recent studies on the treehopper, Alchisme grossa, in forests of the Andes have helped to delineate what these next possible steps in social evolution might be (Torrico-Bazoberry et al. 2014). Alchisme grossa mothers prefer to oviposit on host plants in the Solanaceae. Multiple mothers may oviposit on the same plant, but usually only a single mother oviposits on a leaf. Mothers remain with their offspring for varying amounts of time, with juveniles dispersing as early as the * M. H. Richards [email protected] 1
Biological Sciences, Brock University, St. Catharines, ON, Canada
third larval instar to as late as the fifth (and final) larval instar. When two females find themselves in close proximity, this creates opportunities for social interactions between families. Sometimes groups of juveniles coalesce. When this happens, one female may abandon her brood, and the other may end up guarding a mixed group that includes unrelated juveniles. Observations like these raise fascinating questions about the evolutionary significance of such behaviour. Is group formation simply an accident of proximity or is there some important adaptive function such as enhanced predator protection? Are neighbouring mothers related? Are juvenile herds composed of kin or do they also include non-kin? To answer such questions requires detailed behavioural observations and genetic analyses of relatedness. In
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