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Macrosiphum coryliAmerican hazelnut aphidOn this page: Identification & Distribution Other aphids on the same hostIdentification & DistributionAdult apterae of Macrosiphum coryli (see first two pictures below) have a reddish-brown head and thorax. Their abdomen is greenish in the mid-dorsum, but is suffused with dark reddish-brown pigment laterally and posteriorly (cf. Macrosiphum pseudocoryli in North America, and Macrosiphum skurichinae in Siberia, which both have the abdomen wholly pale green). The antennae are mainly brown and 1.5 times the body length. Their dorsal body hairs are short, not capitate and not borne on tubercles (cf. Corylobium avellanae, which have long, thick and slightly capitate dorsal hairs arising from large tubercles). The dorsal cuticle of Macrosiphum coryli is smooth, and not sclerotic (cf. Macrosiphum vandenboschi in California, which has the dorsal cuticle very wrinkled and strongly sclerotized). The hind tibiae have a paler middle section (cf. Macrosiphum corylicola in Japan, which has the hind tibiae wholly black). The siphunculi are long and tapering, more than three times as long as the cauda, and with subapical polygonal reticulation. The siphunculi are entirely black, contrasting with the pale cauda (cf. Myzocallis coryli, which has very short pale siphunculi). The cauda is finger-shaped, and the anal plate is entire (=not divided). The body length of adult Macrosiphum coryli apterae is 1.6-2.2 mm.
Images above by permission, copyright Claude Pilon, all rights reserved. The alate of Macrosiphum coryli (not pictured) has a brown head and thorax, and a light green abdomen suffused with darker pigment around and posterior to the siphunculi. As with the aptera, the siphunculi of the alate are entirely black contrasting with the pale cauda. Very young immatures are mostly green (see first picture below), but third instars and above have some areas of reddish brown suffusion (see second picture below).
Images above by permission, copyright Claude Pilon, all rights reserved. Macrosiphum coryli is not thought to host alternate, feeding only on the shoot tips and undersides of young leaves of the American hazelnut (Corylus americana) and beaked hazelnut (Corylus cornuta). Hottes & Frison (1932) note this aphid prefers hazelnut growing in somewhat shaded situations; it is rather solitary in habit and not as gregarious as many species of the genus. It is assumed that sexuales develop in autumn, but they have yet to be described. Macrosiphum coryli is mainly found in the more northerly states of the USA and across Canada. Other aphids on the same hostMacrosiphum coryli is recorded to feed on just two species of hazelnut (Corylus americana, Corylus cornuta).
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