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Eriosomatinae : Fordini : Melaphis
 

 

Genus Melaphis

Melaphis aphids

On this page: Melaphis rhois, asafitchi

Melaphis [Fordini]

Melaphis are gall-forming aphids. Antennal tubercles are undeveloped and the front of the head is convex. Compound eyes are absent in the aptera; triommatidia are present in aptera and alate. The antenna of alatae are 6-segmented, with a short terminal process. The primary rhinaria have ciliate margins. Secondary rhinaria are present in alatae, consisting of narrow annuli on antennal segments III-VI. The rostrum is 4-segmented; the apical segment is conical, with apex rounded. The head and prothorax are fused in the aptera, not fused in the alate. The prothorax is without marginal tubercles. The fore wing has reduced venation; the media vein is unbranched, and the branches of the cubitus are close together at the base, then divergent. The abdomen is without pigment except on the last two abdominal tergites. Siphunculi are absent. The cauda is arc-shaped and the anal plate is entire.

The genus Melaphis currently has two named species in North America, but a third species is believed to be present. They host alternate from sumac to moss.

 

Melaphis rhois & Melaphis asafitchi (Staghorn sumac aphid)

Molecular and morphometric analysis have recently been used 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 and Melaphis asafitchi, although the pictures below only represent Melaphis asafitchi.

In spring winged sexuparae of the Melaphis rhois species group migrate from their secondary host - mosses - to their primary host - sumac (Rhus typhina). 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. 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. The fundatrix and her offspring live and feed in the gall. When mature the galls (see first 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. 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.

Each fundatrix gives rise to a series of parthenogenetic generations which greatly increase the number of aphids present in their gall. The second-generation adult aptera in the gall on Rhus is bright yellow, globular, lightly clothed in wax, smaller than the fundatrix and with appendages relatively longer (see second picture below). The antennae have four to six segments, usually five, with a short terminal process. There are wax glands aggregated into facetted plates on all or most of the body segments. The cauda bears 2-4 setae (usually four).

It is possible 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).

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

By late summer, an increasing proportion of nymphs develop, not to apterous adults, but to winged adults (see third picture above). 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. 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.

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.

Both of these Melaphis species accept either smooth sumac (Rhus glabra) or staghorn sumac (Rhus typhina) as their primary host. The ranges of these plant species overlap in the northeastern USA, but Rhus typhina tends to be more northeastern, and is the only species in Canada, and northern New England in the USA. Rhus glabra is widely distributed in the USA south of the Great Lakes east of 100° longitude. There appears to be a similar situation with Melaphis, with Melaphis asafitchi common in the northeastern parts of the combined range, while Melaphis rhois extends further south and west. Melaphis rhois and/or Melaphis asafitchi have also been found on moss as introduced anholocyclic populations in Britain and Sweden.

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Acknowledgements

We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and sp accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

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References

  • Blackman, R.L. & Eastop, V.F. (2006). Aphids on the world's herbaceous plants and shrubs. Vols 1 and 2. John Wiley & Sons.