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Tulip-tree aphidIdentification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:Illinoia liriodendri apterae are spindle shaped and pale green, lightly dusted with wax (see first picture below). There are also yellowish and pink-red forms. The antennae are black except at the bases, and are 1.2-1.6 times as long as the body. The legs are pale green except for black apices to the tibiae and tarsi. The siphunculi are black except at the base, and are 2.3-2.9 times as long as the cauda. They are slightly swollen on the distal half, sometimes bent outwards, and with reticulation on the apical one-tenth to one-eighth. The cauda is pale greenish-yellow and is elongate. The body length of an adult Illinoia liriodendri aptera is 1.7-2.5 mm.
The Illinoia liriodendri alate (second picture above) has a brown thorax, a greenish-yellow abdomen and black antennae and legs except for the bases of the femora. The clarified slide mounts below are of adult viviparous female Illinoia liriodendri : wingless, and winged.
The tulip-tree aphid feeds on undersides of the leaves of tulip tree (Liriodendron tulipifera). Dense populations can build up resulting in large deposits of honeydew on the leaves. Sexual forms occur in autumn. Illinoia liriodendri is native to North America, but in 1998 was found in France. It has since been reported in other European countries and in Japan.
Biology & Ecology:
The host of Illinoia liriodendri is the tulip tree (Liriodendron tulipifera) (see pictures below of leaves and flower), a tree which is native to eastern North America but is the most popular American tree grown in Europe, mostly in parks and gardens. The aphid Illinoia liriodendri was introduced to Europe along with the tree.
The aphids are restricted to the undersides of the leaves where early in the season the clusters of the nymphs can be found behind each of the adult viviparous females (see the picture below).
The colour of the aphid is usually pale green (see first picture below) or yellowish (see second picture below).
A reddish-pink form also occurs, although we have yet to find this form in southern England. The colour of the yellow/green and pink genotypes depends on the relative amounts of different carotenoid pigments present (Andrewes et al., 1971 ).
Illinoia liriodendri overwinters as eggs laid in the autumn, primarily in bark crevices near the buds. In spring the eggs hatch when the leaves begin flushing. Populations build up rapidly on the leaves during the spring and summer.
In southern England we have found Illinoia liriodendri in a number of locations, and it can probably be found wherever its host occurs.
In Wales Baker (2009) recorded Illinoia liriodendri on Liriodendron tulipifera trees at Romilly Park, Barry and Cardiff Bay. In 2008, additional populations were observed on Liriodendron at Roath Park, Cardiff. Populations achieved very high levels in late summer, such that leaves were shiny with honeydew which was foraged by Vespula vulgaris and other insects.
We have found rather few natural enemies attacking the tulip tree aphid in Sussex, although there were a few rather voracious syrphid larvae (see first picture below). There were also a number of predatory anthocorid bugs on the undersides of the leaves which we assume were consuming Illinoia (see second picture below).
Zuparko & Dahlsten (1993) reported twelve primary and 14 hyperparasitoid species of Illinoia liriodendri in Northern California from 1988 to 1990. The most common primary parasitoid was Aphidius polygonaphis which was imported from the eastern United States in the 1970s. The most common hyperparasitoid species were the pteromalids Pachyneuron aphidis and Asaphes californicus. Chrysoperla species were efficient predators when present naturally.
In France Plantagenest & Le Ralec (2007) noted that various European natural enemies appear to attack Illinoia liriodendri. They felt that the introduction of some American parasitoids may be useful for control purposes. In Wales Baker (2009) noted predation by Harmonia axyridis and Syrphus ribesii larvae. Also a few aphids on trees in Cardiff Bay and Romilly Park were parasitized in 2008 by a species of Praon. During damp summer weather, some aphids died after apparent colonisation by fungal pathogens. Bozsik (2012) in Hungary found that natural enemies adequately controlled populations at Debrecen so chemical control was not necessary. Aphid colonies were attacked by Harmonia axyridis adults and larvae and an unknown parasitoid (an Aphelinus spp.).
Damage and control
The main symptoms of damage by Illinoia liriodendri are mildly distorted buds and foliage, and sooty mould on the leaves of host plants due to honeydew build-up. There is also the nuisance caused by honeydew dripping on pavements and parked cars. The attraction of wasps to the honeydew and the resultant stings can cause problems with allergies. In Italy Jucker et al. (2008) reported that attacked tulip trees showed leaf discoloration, sometimes premature defoliation and heavy honeydew accompanied by sooty moulds.
Chemical pesticides were used to control tulip tree aphid in the USA in the late 1980s. Organophosphate insecticides (acephate and diazinon) and insecticidal soaps were initially recommended (Dreistadt & Dalsten, 1988 ), but more recently a range of (possibly) less environmentally damaging control measures have been used (see Bozsik (2012) for a brief review).