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Identification & Distribution

Adult apterae of Aphis genistae are black, and have a black cauda and siphunculi, but are quite thickly coated with wax meal. The hairs on antennal segment III are 0.8-1.3 times the basal diameter of that segment (cf. Aphis ononidis, which has shorter hairs on that segment - only 0.3-0.4 times the basal diameter of that segment). The dorsal abdomen has extensive dark sclerotisation (cf. Aphis fabae, which only has a few small dark spots anterior to the siphunculi). Their siphunculi are quite short, only 0.5-0.8 times as long as the cauda (cf. Aphis craccivora and Aphis cytisorum, which both have siphunculi 1.1-2.2 times the length of their cauda). The body length of adult Aphis genistae apterae is 1.4-2.6 mm.

Both images above by permission, copyright Claude Pilon, all rights reserved.

Aphis genistae alatae are black and heavily-waxed like their apterae, and have 4-8 secondary rhinaria on the third antennal segment.

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

Aphis genistae lives on various broom species such as petty whin (Genista anglica), winged broom (Genista saggitalis) and dyer's broom (Genista tinctoria) and on Spanish broom (Spartium junceum). Wink & Witte (1991) indicate a somewhat wider range of host plants including Laburnum, Cytisus, Petteria, Sophora. Aphis genistae colonies are sometimes attended by ants. This species remains on broom all year, with no host alternation. Oviparae and alate males in develop in September. Aphis genistae is native to Europe, eastward to Ukraine and Turkey. It has also been present in North America for many years, having been first recorded in Massachusetts in 1925 (Foottit et al., 2006).

 

Biology & Ecology

Defense mechanisms

Somewhat unusually, Aphis genistae combines three defence mechanisms against predators: Firstly, the aphids are covered in wax meal, which undoubtedly protects the aphids from some predator groups. Secondly, the aphids are often attended by ants, which will drive away or kill many predatory arthropods. In addition, all Genista species contains quinolizidine alkaloids (Wink et al., 1982). The aphids are able to store these alkaloids, so making themselves toxic to predators. Wink &Witte (1991) identified 52 quinolizidine alkaloids in the plants, 21 of which were present in Aphis genistae. Alkaloid contents were up to 4 mg/g (=0.4%) fresh weight. Feeding tests of predators subsequenly proved this unpalatability using Macrosiphum albifrons, another aphid that consumes alkaloids, although the feeding tests have yet to be carried out using Aphis genistae as prey. It is unknown whether these secondary compounds affect their attendant ants.

 

Other aphids on the same host

Aphis genistae occurs on 7 species of broom (Genista anglica, Genista germanica, Genista humifusa, Genista radiata, Genista saggitalis, Genista scorpius, Genista tinctoria), and on Spanish broom (Spartium junceum) - and, according to Blackman & Eastop, possibly on Cytisus sp..

Acknowledgements

We are especially grateful to Claude Pilon for pictures of Aphis genistae (for more of her excellent pictures see).

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 species 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).

Useful weblinks

References

  • Foottit, R.G., Halbert, S.E., Miller, G.L., Maw, E. and Russell, M. (2006). Adventive aphids (Hemiptera:Aphididae) of America north of Mexico, with notes on intercepted species. Proceedings of the Entomological Society of Washington 108(3), 583-610. Full text

  • Wink, M. & Witte, L. (1991). Storage of quinolizidine alkaloids in Macrosiphum albifrons and Aphis genistae (Homoptera: Aphididae). Entomol. Gener. 15(4), 237-254. Full text

  • Wink, M. et al. (1982). Interrelationships between quinolizidine alkaloid producing legumes and infesting insects: Exploitation of the alkaloid-containing phloem sap of Cytisus scoparius by the broom aphid Aphis cytisorum. Z. Naturforsch. 37, 1081-1086. Full text