Dysaphis pyri

Identification & Distribution:

Micrographs of clarified mounts by permission of Roger Blackman, copyright AWP all rights reserved.

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

Life cycle

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.

Natural enemies

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:

Primary hosts

Dysaphis pyri has been recorded from 8 Pyrus species.

• Blackman & Eastop list 53 species of aphid as feeding on common pear (Pyrus communis) worldwide, and provide formal identification keys (Show World list).

  Of those aphid species, Baker (2015) lists 29 as occurring in Britain (Show British list).

Secondary hosts

• Blackman & Eastop list 22 species of aphid as feeding on hedge bedstraw (Galium mollugo) worldwide, and provide formal identification keys (Show World list).

  Of those aphid species, Baker (2015) lists 16 as occurring in Britain (Show British list).

• Blackman & Eastop list 24 species of aphid as feeding on cleavers (Galium aparine) worldwide, and provide formal identification keys (Show World list).

  Of those aphid species, Baker (2015) lists 18 as occurring in Britain (Show British list).

• Blackman & Eastop list 9 species of aphid as feeding on squincywort (Asperula cynanchica) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 5 as occurring in Britain (Show British list).

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.

Acknowledgements Our particular thanks to Ian Barton for allowing us to reproduce some of his images, shown above, and to Roger Blackman for images of his clarified slide mounts. Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made 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 Alford, D.V. (2000). Pest and Disease Management Handbook. Blackwell, Oxford. Cross, J.V. et al. (1999). Biocontrol of pests of apples and pears in Northern and Central Europe: 2. Parasitoids. Biocontrol Science and Technology 9, 277-314. Full text Evans, K. et al. (2008). A new gene for resistance to Dysaphis pyri in pear and identification of flanking microsatellite markers. Genome 51(12), 1026-1031. Abstract Rakauskas, R. (2004). Recent changes in aphid (Hemiptera, Sternorrhyncha: Aphididae) fauna of Lithuania: an effect of global warming. Ekologija 1, 1-4. Full text Rojo, S. & Marcos-Garcia, M.A. (1997). Syrphid predators (Dipt.: Syrphidae) of gall forming aphids (Hom.: Aphididae) in Mediterranean areas: Implications for biological control of fruit trees pests. Entomophaga 42(1/2), 269-276. Full text Sauphanor, B. et al. (1993). Mean term effects of pesticides on beneficials in pear orchards: a field trial evaluation. Journal of Applied Entomology 116(5), 467-478. Abstract Savary, A. (1953). Le puceron cendre du poirer (Sapaphis pyri Fonsc.) en Suisse romande. Landwirtschaftliches Jahrbuch der Schweiz 67, 247-314.