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Genus Mindarus [Mindarini]
Wingless Mindarus forms have a fused head and pronotum and well well-developed wax glands which produce a covering of wax wool. Their antennae are short. The siphunculi are pore-like and the cauda is bluntly triangular. Winged forms have forewings with an elongate pterostigma, tapering to a point at the wing apex. Oviparae and males are wingless and reduced in size.
There are 8 or more Mindarus species worldwide, feeding on the growing tips and young cones of spruces or firs. They have a sexual stage in the life cycle, but there is no host alternation and Mindarus aphids are not attended by ants.
Mindarus abietinus (balsam twig aphid)
The wingless viviparae of Mindarus abietinus are yellowish green and covered with wax powder and long tendrils of accumulated wax (cf. Prociphilus fraxinii and Prociphilus bumeliae, which are also wax covered, but feed on the roots of Abies). The antennae and legs are distinctly darker. Wax pore plates are almost always absent from the prothorax and abdominal tergites I & II, and only constantly present on abdominal tergites VI & VII (cf. most other Mindarus species feeding on Abies, which have wax pore plates on the prothorax and often also on abdominal tergites II-VII). The body length of apterae is 1.7-2.0 mm.
The winged viviparae of Mindarus abietinus (see second picture above) have dark dorsal abdominal cross-bands. Antennal segment III has 12-27 rhinaria in a single row, mostly extending across the complete segment width. The alate body length is 1.5-2.7 mm.
The balsam twig aphid is found on young shoots of fir (Abies species) especially silver fir (Abies alba) and Nordmann fir (Abies nordmanniana). Eggs hatch in spring and there are then three generations. Small apterous sexual forms are produced in June and the females lay eggs which hatch the following spring. Mindarus abietinus is found throughout Europe, as well as the Middle East, Pakistan and possibly India and parts of the Far East. It may cause serious damage or kill young shoots, or cause deformation and loss of needles. There is also some evidence that infestations affect susceptibility to spruce budworm.
Mindarus obliquus (waxy spruce aphid)
Adult apterae of Mindarus obliquus are yellowish green, but appear whitish due to their covering of wax wool (see pictures below). The eyes of Mindarus obliquus usually have several facets in addition to the triommatidia (cf. Mindarus abietinus, which has eyes consisting only of triommatidia). The apical rostral segment (RIV+V) is about 0.5 times as long as the base of antennal segment VI. Marginal wax pore plates are usually present on abdominal tergites I-VII or II-VII, but spinal and pleural wax pore plates are reduced or absent except on their most posterior tergites. Small siphuncular pores are present in the apterous morph and the embryo, but not in the fundatrix (cf. Mindarus abietinus, which has no siphuncular pores in either the aptera or embryo). The body length of the Mindarus obliquus aptera is 1.2-1.9 mm.
Two images above by permission, copyright Claude Pilon, all rights reserved.
The winged viviparae of Mindarus obliquus have dark dorsal abdominal cross-bands. They have 7-13 secondary rhinaria on antennal segment III, and 1-4 rhinaria located near the distal end of segment IV (cf. Mindarus abietinus, which has 14-27 rhinaria on segment III and usually only one rhinarium on segment IV). Antennal segment III is 0.23-0.32 mm long, and usually less than 0.31 mm (cf. Mindarus abietinus, where that segment is 0.31-0.49 mm long, but usually more than 0.31 mm). Alatae usually have the media of their forewing once-branched. The body length of alate Mindarus obliquus is 1.0-1.6 mm (cf. the alate of Mindarus abietinus, which is larger, having a body length of 1.5-2.7 mm).
Mindarus obliquus is known to feed on several species of spruce especially Engelmann spruce (Picea engelmannii), white spruce (Picea glauca), and Sitka spruce (Picea sitchensis), but not on any firs (Abies spp.) which supposedly only host Mindarus abietinus. However, the molecular methods used to identify these aphids also indicated Mindarus obliquus for several samples from firs in Quebec, Canada (these specimens are not pictured above) - which suggests we have much more to learn about the host preferences of Mindarus species. Mindarus obliquus is thought to have originated in the Nearctic region given it does not feed on Palaearctic spruces such as Norway spruce (Picea abies). It feeds between the needles on new shoots in spring, but it does not deform the needles. The life cycle is holocyclic with small apterous sexuales developing in June-September. Mindarus obliquus is found in Canada and Alaska (and possibly some other northern U.S. states), plus Europe, east to Turkey (and possibly China).