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Pear-bedstraw aphidOn this page: Identification & Distribution Biology & Ecology Life cycle Natural enemies Other aphids on the same host Damage & Control
Identification & Distribution:
Dysaphis pyri induce yellowed pseudogalls on Pyrus (pear) in spring (see first picture below) (cf. the similar yellowed or reddened pseudogall of Melanaphis pyraria which rolls the leaves of pear transversely or diagonal to the mid-rib). Adult apterae of Dysaphis pyri are medium to rather large globe-shaped, light brownish-red (see second picture below) to dark grey-brown aphids (see third picture below), thickly coated with grey wax meal . The antennae are pale yellow near the base, but darker towards the apex. The first 5 abdominal tergites have a double row of small dark sclerites (cf. Dysaphis plantaginea which has no small dark dorsal sclerites). Hemispherical marginal tubercles are usually present only on abdominal tergites I-V. The siphunculi are black and perpendicular to the body, and are more than 0.3 mm. in length ( cf. Dysaphis plantaginea which has longer siphunculi, greater than 0.3 mm. in length). The siphunculi are 3.4-4.1 times their diameter at midpoint, and longer than the cone-shaped cauda. The adult Dysaphis pyri aptera has a body length of 2.1-3.2 mm.
Very young Dysaphis pyri are a pale yellowish brown, with reddish suffusion around the bases of their siphunculi (see first picture below). Spring migrant alates have the abdomen brownish-red with a black dorsal patch. They have 23-36 secondary rhinaria on antennal segment III, 2-10 on segment IV and 0-1 on segment V.
The micrograph below shows an adult aptera dorsal view in isopropyl alcohol.
The primary host of Dysaphis pyri is common pear (Pyrus communis). Leaves and shoots are yellowed and distorted to form a pseudogall. After about three generations on pear, alatae are produced which migrate to the secondary hosts. These are bedstraws, especially hedge bedstraw (Galium mollugo) and cleavers (Galium aparine) and sometimes squincywort (Asperula cynanchica). Dysaphis pyri may form colonies on the roots and prostrate stems, where it is attended by ants. Dysaphis pyri is found throughout Europe, the Middle East, North Africa and Central and South Asia, and has been introduced into the USA.
Biology & Ecology
Savary (1953) studied the life history and population biology of Dysaphis pyri in Switzerland.
The pseudogall of Dysaphis pyri (see picture below) is rather similar to that of Melanaphis pyraria, but is usually only slightly yellowed and not reddish.
Dysaphis pyri sometimes 'shares' its pseudogalls with other aphids. The picture below shows a mixed colony of Dysaphis pyri and Rhopalosiphum oxyacanthae - the latter are the small green aphids. Mixed species colonies are quite often found in aphid galls, with other species taking advantage of the improved nutrition and protection within the gall.
The aphid below appears to be an aberrant specimen of Dysaphis pyri which has not developed its wax coating. The smaller aphids are its nymphs.
After about 3 generations on pear, Dysaphis pyri produces alate emigrants which colonise the roots and prostrate stems of bedstraws, such as hedge bedstraw (Galium mollugo) and sweet woodruffe (Galium odoratum), where it is usually attended by ants. The picture below shows a colony on the runners of sweet woodruffe in October.
Image above copyright Ian Barton, all rights reserved.
The only predators we have so far found attacking Dysaphis pyri within the pseudogall are syrphid larvae such as the one shown below.
Rojo & Marcos-Garcia. (1997) looked at syrphid predators of pear tree aphid pests. Larvae of the pipizine syrphid Heringia heringii were more abundant than those of other syrphid species. More than 40% of Heringia heringii larvae were collected on Dysaphis pyri colonies.
Rakauskas (2004) reported the appearance of large numbers of Dysaphis pyri necessitating chemical control in Lithuania in 2002. Aphids could not be found on the summer host Galium. so it was concluded these were probably airborne summer migrants, possibly the result of global warming.
Other aphids on same host:
Dysaphis pyri has been recorded from 8 Pyrus species.
Damage and control
Dysaphis pyri is the most important aphid pest of pear causing severe direct feeding damage to both shoots and fruits. Growing shoots and leaves are distorted and yellowed, and heavy infestations check plant growth. Large quantities of honeydew are produced, further affecting growth.
Insecticide treatment is still the primary method of control. Alford (ed) (2000) recommends application of insecticides if any Dysaphis pyri are detected before flowering. From petal fall onwards, a suitable threshold is if 1% of trees is infested. Suitable insecticides include the organophosphates chlorpyrifos and dimethoate, the pyrethroid cypermethrin, the alkaloid insecticide nicotine, soap concentrate containing fatty acids and rotenone. A tar oil winter wash can be used against overwintering eggs.
Sauphanor et al. (1993) carried out a field trial to test the nontarget effects of pesticides on beneficial insects in a pear orchard near Avignon, France. The treatments were applied in April and May to affect the first generation of another pest, Dasineura pyri. Observations were carried out for 15 days after each of the treatments (amitraz, diazinon and pyrethrins + rotenone) to study the effect on Psylla pyri, Dysaphis pyri, and the main natural enemies present. It was concluded that earwigs (Forficula auricularia) play a major role in the regulation of Psylla pyri populations.
So far no resistant varieties of pear have been developed, although Evans et al. (2008) has identified a new gene for resistance to the aphid.
Cross et al. (1999) reviewed biocontrol of pests of apples and pears by parasitoids in central and northern Europe. Only Ephedrus persicae, a species specialising in leaf-curling aphids in trees, is recorded as attacking Dysaphis pyri and then only at a low level of effectiveness. The authors suggested that host plant alternation may diminish the effectiveness of parasitoids for Dysaphis pyri.