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Hazel aphid, Filbert aphidIdentification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:Winged adult viviparae of Myzocallis coryli (see first picture below) are pale yellow to yellowish white. Their antennae are ringed with black, with a terminal process that is 2.05-2.55 times the length of the basal part of antennal segment 6. The forewing has a black spot at the base of the pterostigma. The body length of Myzocallis coryli alates is 1.3-2.2 mm.
Immature morphs (see second picture above) have the body hairs, and sometimes a few basal antennal hairs, capitate and very much longer than those of adult viviparae. Myzocallis coryli oviparae are orange-yellow in colour, but when examined in alcohol they appear quite pale. Like the immatures, the oviparae have long capitate hairs.
The hazel aphid lives on the undersides of leaves of hazel (Corylus species). Like Myzocallis carpini, it may become abundant when its host is used for hedging. Myzocallis coryli is found in Europe, south-west Asia, north Africa, Japan, New Zealand, western North America, and South America.
Biology & Ecology:
Myzocallis coryli lays its eggs in October on two or three year old twigs and branches of hazel.
The eggs are mostly positioned singly in crevices, on leaf scars around the buds (see picture above) and under the bark scales of hazel trees (El Haidari, 1959 ). Their eggs are elongate-oval in shape and are pale yellow when first laid, but soon turn shiny black.
The eggs hatch to give nymphs which initially feed on the swelling buds, and then on the undersides of the leaves. These mature to winged adult fundatrices in 2 to 3 weeks, and then give birth to large numbers of future viviparae.
The summer viviparae feed on the undersides of the leaves (see picture below) as well as on young stems and the developing nuts.
In the US El Haidari (1959) working in Oregon, USA, found that numbers peaked early in the year in May and June. By late July numbers had usually dropped dramatically. Tuncer et al. (1997), in Turkey, found that their population rapidly increase until the end of June, then declined, but showed a brief increase in early November when the sexual forms occurred. Similarly Yarahmadi & Rajabpour (2012), in Iran, found that the population peaked at end of May or beginning of June (albeit this was just two years data). In Britain, Naeem & Compton (2000) found numbers peaked in June in forest plots, but in late July in agroforestry tree rows.
With the approach of autumn the viviparae give birth to sexuparae (aphids which give birth to the sexual generation of males and egg-laying females - known as oviparae). The sexual forms feed on the underside of the old senescing leaves before developing to winged males and wingless oviparae. The sex ratio is approximately 5 to 1 in favour of females. The oviparae are whitish, yellow or orange yellowish (see pictures below), and are elongated at the posterior end.
Myzocallis coryli shares hazel as a foodplant with another host specific aphid, Corylobium avellanae (see picture below), but there is usually a clear cut niche-separation. Myzocallis coryli mainly feeds on the leaves, whilst Corylobium avellanae mainly feeds on the young shoots.
Only rarely can one get both species in the same photograph. In the picture above the single pale green nymph is Myzocallis coryli, and Corylobium avellanae is apple-green.
We have observed very few predators attacking populations of Myzocallis coryli in seminatural mixed woodland, although we have found anthocorid bugs predating Corylobium avellanae on hazel (known as 'filbert' in USA).
However, the apparent low number of predators most likely results from Myzocallis coryli populations normally being maintained at low levels by natural enemies.
Messing & AliNiazee (1986) studied the impact of predaceous insects on populations of Myzocallis coryli in Oregon, USA by chemical and mechanical exclusion methods. Filbert trees from which predators were excluded had significantly higher aphid populations than trees with predators. The feeding potential of one coccinellid, Adalia bipunctata, and three mirids, Deraeocoris brevis, Heterotoma meriopterum and Compsidolon salicellum was determined in the laboratory. Predators consumed from 5 to 65 aphids daily, with the coccinellid consuming more than the mirids. The data showed that the predator complex is an important factor regulating aphid populations in filbert orchards of Oregon. Aguilera & Pacheco (1995) surveyed the natural enemies of Myzocallis coryli on hazelnuts in Chile. Four species of coccinellids, the syrphid Allograpta pulchra, the cecidomyiid Aphidoletes sp. and the hemerobiid Hemerobius sp. were found.
Damage and control
Messing et al. (1988) found some worrying positive responses of Myzocallis coryli populations to carbaryl treatment. Field applications of carbaryl and other insecticides against the Myzocallis coryli in hazelnut orchards of western Oregon resulted in initial population reductions for all chemical treatments. However, significant resurgences occurred on carbaryl treated trees. In some orchards the aphids rebounded to levels well above those on untreated trees. Other insecticides were as toxic to aphidophagous predators as carbaryl, indicating that natural enemy mortality was not the only factor leading to carbaryl-induced resurgence. Laboratory tests showed that aphids exposed to low dose leaf residues of carbaryl produced significantly greater numbers of offspring than did untreated aphids. Tuncer & AliNiazee (1998) looked at the acute and chronic effects of neem on Myzocallis coryli.
Messing & AliNiazee (1989) used classical biological control for Myzocallis coryli in Oregon, USA. Hazelnut orchards in Spain, France, and Italy were searched for parasitoids of the filbert aphid, Myzocallis coryli. A biotype of Trioxys pallidus Haliday was found to parasitize the aphid throughout western Europe. Wasps were imported, quarantined, mass-reared, and released in Oregon orchards. The wasp successfully attacked and completed its development on Oregon populations of the filbert aphid. A greenhouse culture of the parasitoid was maintained continuously for over 50 generations, and approximately 30,000 adult wasps were released in western Oregon. Overwintering survival has been documented in at least 12 different locations. In 3 commercial hazelnut orchards, the parasitoids proved capable of reducing aphid population peaks by 33-48%.
AliNiazee (1997) reviewed integrated pest management for hazelnut cultivation. Insect pests are a major detriment to hazelnut cultivation throughout the world. Damage estimations vary form 20-50% depending upon the cultural practices, treatment efficacy, and environmental conditions. Most growers depend on the application of harsh, broad-spectrum pesticides to control these pests. This causes disruption of natural enemies, development of resistance in target pest, secondary pest, secondary pest outbreaks, deposition of residues on treated products and massive environmental contamination. If undisturbed, the biological control is effective against most hazelnut insects. Development and utilization of integrated pest management (IPM) programs based on ecologically compatible approaches including microbial, biological and chemical controls with improved utilization of insect monitoring programs have been adapted in many hazelnut growing countries of the world.