Ants, aphids and Black Currants

ANTS, APHIDS AND BLACK CURRANTS ERIC PARSONS

My wife and I are both keen gardeners and we grow vegetables and soft fruits in addition to cultivating a formal garden. More than five years ago we decided to stop using pesticide sprays, partly because we obtained as much interest from the pests as f r o m the crops themselves.

Generally aphids do not have an unacceptable impact on our garden crops today and we like to think that this is the result of natural regulation by predators like ladybirds, lacewings and hover flies. The exception is the Black Bean Aphid, Aphis fabae Scop., populations of which erupt prolifically, particularly on Broad Bean, Viciafaba, where the pods are often affected before they can form. It has been our experience that this species needs to gain an early foothold to cause significant damage. Other plants in the garden can be affected. These include, strangely enough, Rhubarb, Rheum rhaponticum, infusions of which are widely used as an 'organic' aphicide spray (see footnote). The black aphids proliferate mostly on the growing point and developing shoots, and the technique well known to gardeners of pinching out these vulnerable parts on Broad Bean plants as soon as the aphids are seen has been effective for us in controlling these insects.

Black Ants, Lasius nigerL., are atracted to the extra-floral nectaries found at the black spots on the stipules of Broad Bean plants, as they are to Common Vetch, Vicia sativa L. The ants are also attracted to the Black Aphids, feeding on the 'honeydew' they excrete, and the ants may provide early protection to invading Black Aphids. The activity of Black Ants on plants has come to suggest the presence of aphids to us and the need for closer inspection of our garden.

We have a bed of soft fruits containing 3 Black Currants, Ribes nigrum, 3 Red Currants, R. sativum, and 2 Gooseberries, R. grossularia, in addition to some cane fruits, on the garden's light, sandy soil. Over the years the relatively low yield of the Black Currants in comparison with the other bushes has been a puzzle, which might have been resolved earlier if we had been more observant. It had been clear from an early stage that the potential number of fruits was never reached, with an unacceptable number of 'blind' stalks at harvest.

We thought this to be the outcome of poor pollination of the Black Currant flowers, which appeared earlier in the spring than those of the Red Currants.

We therefore tried to establish artificial nesting sites for both bumble and solitary bees. The Tawney Mining Bee, Andrena armata, is particularly in evidence at the right time to pollinate when there are only a few emergent Footnote: E v e n m o r e unlikely f o o d plants f o r s o m e aphids are Nicotiana spp., tobacco plants. T h e y not only contain nicotine, an e x t r e m e l y effective aphicide, b u t are o f t e n c o v e r e d by sticky, glandular hairs. In spite of this, Nicotianas can be heavily infested with a p h i d s , which f e e d on tissue (the p h l o e m ) which is f r e e f r o m nicotine.

(Editor)

Trans. Suffolk Nat. Soc. 24

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bumble bee ( B o m b u s spp.) queens working. Over 3 years solitary bees have rejected short lengths of bamboo cane mounted in bundles on the posts of the fruit cage, and bumble bees have shown little interest in partly buried flower pots containing artificial mouse nests, but we continue to explore ways of providing hospitality for these useful and attractive insects.

However, we now think that the problem with the Black Currants is due to Blackbirds taking the immature, green berries, and not to the flowers failing to set. The Black Currant fruit develop on the new wood and are much more conspicious than those of the Red Currant, which are on the old wood where they are obscured by foliage, Nets will go up much earlier on the fruit caee in 5 1988!

Aphids found feeding on the bushes last year were identified as Currant Aphids, Aphis grossulariae Kaltb., They are a deep, light green, with antennae shorter than the body, cylindrical cornicles with dark tips, and blunt, paired lateral tubercles on the abdomen. They attack Red, Black and White Currants, Gooseberry and the Guelder Rose, Viburnum opulus. They can be very abundant and damaging on Ribes spp., where they are found in dense clusters on the apical leaves and the young wood of the tips of the shoots from May to July and again in the Autumn.

Like all other aphids, the Currant Aphid excretes honeydew, and it is attended by the Black Ants which are prevalent throughout our garden. In mid-July 1987 the ants constructed curious earth cells round the Currant Aphids that were feeding on one of the Black Currant bushes. The aphids were entirely enclosed in the earth cells, which were up to 1 cm across, but were still being attended by the ants, which were commuting up and down the branches. They must have carried the earth up the bush, making cells about 80 cm f r o m the ground on the leading shoots of new wood rising from the cenre of a bush 120 cm high. When the cells were found the weather was dry and warm, in a summer which had been mainly cool and wet.

Eric Parsons 41 Dover Road, Ipswich, IP3 8JQ

Trans. Suffolk Nat. Soc. 24