Life cycle

The commonest species on apple, Edwardsiana crataegi, overwinters as eggs laid in the autumn beneath the bark of twigs or small branches of fruit trees.

• Eggs hatch in April to early May.
• Nymphs feed until mid-summer.
• New adults appear in late July and August, laying eggs in or near the mid-vein on the undersides of leaves.
• Second generation nymphs occur from August onwards and become adults in the autumn.

Edwardsiana rosae has a similar life cycle but overwintering eggs are laid on rose.

• Apple orchards are invaded by a migration of adults to summer hosts in June.
• There is a return migration of second generation adults to rose to lay eggs in the autumn.

Pest status

Leafhoppers are minor pests of apple and pear but they have increased in abundance in apple orchards in recent years and have become troublesome in some orchards.

Other hosts

• The commonest species in apple orchards currently, Edwardsiana crataegi, infests fruit trees including apple, pear, cherry, damson and plum.
• Hawthorn is its main wild host but it also occurs on a wide range of other rosaceous plants.
• The second most common leafhopper, Edwardsiana rosae, also has a similarly wide host range including fruit trees, gooseberry, blackberry, raspberry, strawberry, hop and nut.
• The leafhopper Alnetoidia alneti occurs on alder windbreaks and also infests apple, cherry and plum.

Varietal susceptibility

There are considerable differences in the susceptibility of apple varieties but these have not been adequately quantified. Some of the newer desert varieties seem particularly susceptible.

Distribution

The main species, Edwardsiana crataegi, is widespread and abundant in apple orchards.

Damage

Leafhoppers feed on the non-vascular leaf tissue (mesophyll cells), puncturing the cells and withdrawing the sap.

• This causes white speckling of the leaves visible from above and below.
• Damage is usually most intensive on older leaves in the centre of the tree.
• When populations are very high, leaves of apple trees can become bleached by the end of the season.
• The photosynthetic activity of the tree is reduced as the chlorophyll content of cells is removed.
• This can adversely affect tree vigour and return bloom.
• Fruit surfaces below leaves which are fed on can become contaminated by numerous small brown spots of excrement.
• This contamination is fairly easily washed away by water, including by rain, during post-harvest drenching or grading.
• Some leaf hoppers transmit diseases.
• The leafhopper Fieberiella flori is a vector of the phytoplasma disease that causes apple proliferation disease. The vector does not occur in the UK.

Recognition

• Leafhoppers that occur on apple in the UK are small (mostly 3-5 mm long) slender insects, usually green or yellow in colour (though some species are brightly coloured), found mainly on the undersides of leaves associated with the speckling damage they cause to foliage.
• They are active insects and jump and fly readily especially in warm conditions.
• The various species that occur on fruit trees are generally similar in appearance though some have characteristic markings on their body or wings.

Adult
The commonest species are 3-4 mm long, pale yellow with a yellow abdomen.

Nymph
Nymphs are like adults but smaller and are without fully developed wings.

Monitoring

Leafhopper populations are best monitored by visual inspection for the characteristic speckling damage which occurs initially on older leaves in the centre of the tree, and for the leafhoppers themselves which are often present on the undersides of damaged leaves.

• When populations are high, brushing the foliage or shaking the tree will cause large numbers of adults to leap from the tree and make a short flight before re-settling.
• In cool conditions, leafhopper populations can be estimated by beat sampling. However, in warm conditions most individuals simply fly away and do not fall into the beating tray.
• Another approach is to use yellow or white sticky traps.
• Economic thresholds have not been developed.
• However, damage is only likely to be significant if a large proportion of the leaf surface becomes bleached in mid or late summer.

Forecasting

Useful forecasting methods have not been developed for the leafhopper pests of apple.

Chemical control

A spray of an approved insecticide should be applied in summer against adults and nymphs if leaf damage starts to become unsightly and is increasing.

• Acetamiprid (Gazelle), though only specifically recommended by the manufacturer for control of aphids, may give incidental control of leafhoppers.
• A full approval for spirotetramat (Batavia) on apples for the control of sucking insect pests will control leafhoppers, but growers may prefer to reserve its use for more difficult to control pests such as woolly aphid or rosy apple aphid. It must be applied after flowering and works best when pests are moving from brown wood to green tissue. It will prevent population build-up but does not offer pest ‘knockdown’.
• A recent EAMU for Flipper (fatty acids) has increased the available options should growers wish to reserve other insecticides for control of pests later in the season. Although recommended for control of aphids, mites and blossom weevil, it is expected to offer incidental control of leafhoppers when applied for these pests. It is known to complement the use of Batavia as it provides quick ‘knockdown’.
• Synthetic pyrethroids are also effective but they are harmful to the orchard predatory mite Typhlodromus pyri and many other natural enemies and should only be used as a last resort where no alternative can be used.

Cultural control

There are few cultural control approaches for this pest. Spatial isolation of orchards from wild alternate hosts may be beneficial, especially for species that have an obligate alternative host (e.g. Edwardsiana rosae).

• Avoiding using broad-spectrum insecticides to allow parasites and other natural enemies to flourish will help.
• However, leafhoppers are often very abundant on unsprayed apple trees.

Natural enemies

Predatory insects and spiders
Leafhoppers appear to have few natural enemies. They are preyed on by nabid bugs and spiders.

Parasitic flies and wasps
Parasitic flies and wasps are the most important natural enemies of leafhoppers.

• Pipunculid parasitic flies in the genus Chalarus lay their eggs singly into the abdomen of third to fifth instar leafhopper nymphs.
• The larva of the parasites have two instar stages, the second only occurring in the adult host.
• The parasite larva consumes most of the host’s tissues and emerges through its skeleton. Up to 20% parasitism has been recorded.

Dryinid parasitic wasps in the genus Aphelopus also inject their eggs singly into the abdomen of leafhopper nymphs.

• The egg hatches when the nymphs are mature or when they reach adulthood.
• Dryinid parasitic wasps have five larval instars but only for the first two instars is the body of the parasite entirely within the host’s body.
• The late second and subsequent instars are semi-external.
• The parasites head and part of its tail remain inside the host but the remainder is external and curves between the attachment points in an arc.
• The external parts contain a brown/black sack, which contains moulted skins.
• Development takes about six weeks.
• The larvae then splits the sack with the head remaining attached to the host while the parasite consumes it.
• The larva then moves away and spins a cocoon in which it pupates. Aphelopus species can cause up to 20% parasitism.

Another group of parasitic wasps, the mymarids known as fairy flies (Anagrus, Anaphes, Gonatocerus and Polynema species), are egg parasite and can sometimes cause high levels of parasitism.

Biological control

Biological control approaches for leafhoppers on apple have not been developed.

• Inundative releases of parasitic wasps that parasitise eggs have been use to effect to control other leafhopper species on other crops in other countries.
• However, this approach is likely to be uneconomic.

Biotechnological control

Biotechnological control measures have not been developed.

 

Further reading

Charles, J. G., Walker, J. T. S. & White, V. 1994. Resistance of Froggatt’s apple leafhopper Edwardsiana crataegi Douglas, to azinphos-methyl. Proceedings of the Forty Seventh New Zealand Plant Protection Conference, 333-336.

Jay, C. N. & Cross, J. V. 1996. Survey of leafhopper damage to apple 1996. Report of APRC project SP106 issued 3 January 1997, 14pp.

Krczal, G. Krczal, H & Kunze, L. 1989. Fieberiella flori (Stal.), a vector of apple proliferation agent. Acta Horticulturae 235, 99-106.

MacNeil, J. D., Hikichi, M. & Downing, R. S. 1987. An investigation of the effects of seasonal changes, leaf maturity, nitrogen deficiency and leafhopper injury on the chlorophyll content and diffuse reflectance spectroscopic properties of orchard leaves. International Journal of Environmental Analytical Chemistry 31, 52-62.