Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Large raspberry aphidIdentification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:The large raspberry aphid (Amphorophora idaei) only feeds on raspberry and the apterae (see first picture below) are usually greenish white or pale yellow (cf. Amphorophora rubi which is darker green and feeds on blackberry). The antennal terminal process is usually more than seven times the length of the last two segments of the rostrum. The siphunculi are slightly swollen on the apical part and 2.1 to 2.6 times the length of the cauda. The cauda is short and triangular. The body length of Amphorophora idaei apterae is 2.7-4.1 mm.
The alate Amphorophora idaei (see second picture above) is of similar size but has a brown head and thorax, and has the distal half of the siphunculi darkened.
Blackman et al. (1977) separated this species from Amphorophora rubi by cytological studies, which showed that the chromosome complement of Amphorophora occurring on red raspberry in Europe differed from that of Amphorophora sampled from blackberry (2n = 18 and 20 respectively).
The clarified slide mounts below are of adult viviparous female Amphorophora idaei : wingless, and winged.
The large raspberry aphid has a sexual stage in its life cycle and does not host alternate. Oviparae and winged males appear in October-November. Amphorophora idaei feeds on the underside of leaves of raspberry (Rubus idaei) and is found throughout Europe.
Biology & Ecology:
McMenemy et al. (1976) has provided an excellent review of the biology of the European large raspberry aphid (Amphorophora idaei) and its role in virus transmission and resistance breakdown in red raspberry.
The overwintering eggs hatch in early March to give the fundatrices. The nymphal fundatrix is distinguishable from nymphs in later generations by the presence of two rows of dark spots and bristles on the dorsal surface. These spots fade in the third and fourth instars (Dicker, 1940 ).
The mature fundatrix produces large numbers of nymphs which feed at leaf tips before moving to the underside of the leaves (see picture below). The apterous nymphs and adults are very mobile and drop from the plant when they are disturbed (Converse, 1987 ).
These alatae begin to migrate to new canes on the host plant or colonize new plants. Oviparae and males begin to appear in October. Eggs are deposited near the base of the canes of the host plant from October right through until December, where they remain until the next March. The eggs are yellow-green when first laid but soon change to shining black.
Mitchell et al. (2007) looked at interactions between Amphorophora idaei and three common aphid parasitoids: Aphidius colemani, Aphelinus abdominalis and Aphidius ervi. Only Aphidius ervi successfully parasitized the aphid, but parasitism levels were low. Attack rates were significantly lower on resistant plants than on susceptible plants.
Damage and control
The European large raspberry aphid, which may carpet the undersides of the leaves of some raspberry varieties (see picture below), is the most important vector of viral diseases affecting commercially grown red raspberry (Rubus idaeus) in Northern Europe.
Amphorophora idaei transmits four known viruses: Black raspberry necrosis virus, Raspberry leaf mottle virus, Raspberry leaf spot virus and Rubus yellow net virus. All four of these viruses are believed to be naturally transmitted during feeding on infected plant tissue, with the virus being picked up by the aphid's stylet.
The most effective method of disease control is the planting of red raspberry cultivars genetically resistant to the aphids (McMenemy et al., 1976 ). To date, no gene has been identified in Rubus germplasm that can convey resistance to the virus itself, so management will depend on controlling the aphid vector. Until recently, this has been largely successful at controlling the spread of the viruses transmitted by Amphorophora idaei.
Unfortunately strong selection pressures have resulted in Amphorophora idaei overcoming genetic resistance in many raspberry cultivars, and most insecticides are now ineffective. The hope for the future is to combine host plant resistance with biocontrol agents such as parasitoids and predators (Birch et al., 1997 ). Hopefully these approaches will be facilitated by the development of new molecular and genetic tools, and the extensive use of polytunnels which will increase the effectiveness of parasitoids.