Melaphis rhois species group
Melaphis rhois & Melaphis asafitchi

In spring sexuparae (see first picture below) of the Melaphis rhois species group migrate from their secondary host - mosses - to their primary host - sumac (Rhus typhina). The eyes of the winged sexuparae are huge and their abdomen is very short compared to the thorax. On the sumac the sexuparae produce male and female nymphs (future sexuales). These nymphs do not feed, but moult four times over a few days to give males and oviparae, both wingless. These sexual females mate under the growing stems of sumac and two to three weeks later, each female lays a single egg, which immediately hatches to give the first instar fundatrix (these unusual sexual females are known as ovoviviparous). Each immature fundatrix moves to the end of a stem and waits, sometimes for a few days, for a leaf to begin unfolding. It then feeds on the top of the leaf and induces a gall, on the leaf underside. This gall is initially green, hairy, and speckled with red (see second picture below). The base of the gall is not located on a leaf vein but nearby, with the opening on the side of the aphid. The fundatrix and her offspring live and feed in the gall.

Note: The staghorn sumac aphid was first described by Asa Fitch in 1866 under the name Byrsocrypta rhois. It was subsequently moved to the genus Melaphis. More recently, Footit & Maw (2018) used molecular and morphometric analysis to show that there are at least three sympatric cryptic Melaphis species in America which have previously been dealt with under the name Melaphis rhois. We cover two of these on this page: Melaphis rhois (Fitch) and Melaphis asafitchi Footit & Maw. Apart from the first three pictures on this page, all the pictures on the primary host are of Melaphis asafitchi. Those on the secondary host can only be identified to Melaphis rhois species group.

Images above by permission, copyright Claude Pilon, all rights reserved.

When mature the galls (see picture below) are globular to pyriform, largely mottled reddish-pink in colour in exposed locations, but usually with pale yellow to yellow-green areas on the side protected from the sun. Pale areas are more extensive in shaded locations. The gall surface is often irregular to weakly lobed. The galls are up to 50mm in length and up to 45mm at their greatest diameter.

Image above by permission, copyright Claude Pilon, all rights reserved.

Each fundatrix gives rise to a series of parthenogenetic generations which greatly increase the number of aphids present in their gall. The first picture below shows the aphids present in a gall in summer (early August). All the adults are apterous - even the late instar immatures show no sign of developing wing buds. These aphids are rather lightly clothed in wax. The second picture below shows two adult apterae.

Images above by permission, copyright Claude Pilon, all rights reserved.

The second-generation adult aptera (fundatrigenia) in the gall on Rhus is bright yellow, globular, smaller than the fundatrix and with appendages relatively longer. The antennae have four to six segments, usually five. The terminal process of the ultimate antennal segment is 0.15 times the base of that segment. The trochanter is fused with the femur without obvious demarcation. There are wax glands aggregated into facetted plates on all or most of the body segments. The cauda bears 2-4 setae (usually four). Recent research by Footit & Maw (2018) enables us to distinguish between two of the species in the Melaphis rhois species group (Melaphis rhois and Melaphis asafitchi) when they are on the primary host. For Melaphis rhois the length of the apical rostral segment (RIV+V) of adult apterae on Rhus is > 68 µm long (cf. Melaphis asafitchi on Rhus, which has RIV+V of adult apterae < 68 µm long). Footit & Maw also give thresholds and discriminating functions for distinguishing other morphs of those two species.

By late summer, an increasing proportion of nymphs develop, not to apterous adults, but to winged adults (see pictures below). In mid-September the gall splits open, and these emigrant alatae migrate to mosses, often by simply dropping to moss-covered ground in the vicinity of their sumac bush. The emigrant alata has antennae with five to six (usually five) segments and a body length of 1.2 mm.

Images above by permission, copyright Claude Pilon, all rights reserved.

On the moss where they have flown, the emigrants give birth to grey wax-covered nymphs which, once adult, produce a second generation of yellow-coloured exules which live enveloped in filamentous wax (see pictures below).

Images above by permission, copyright Claude Pilon, all rights reserved.

Their life cycle on mosses is not fully known. Given the protracted period during which emigrant alatae leave the gall, one possible sequence of events is that early-born exules mature in the autumn and produce larvae that diapause and develop into the sexuparae in the following spring. These sexuparae then migrate to sumac and produce the sexual forms. The development of later-born exules on moss is delayed, and they overwinter as early instars which mature and produce summer moss generations. This is but one of five possible 'trajectories' proposed by Footit & Maw (2018) for the part of their life cycle on mosses.