Insecta, Homoptera, Aphididae .
Description, Biology, Life Cycle, Damage, Common Names, Images
This aphid is heteroecious. Summer hosts are cultivated hop, wild hop (Humulus lupulus and Humulus japonicus), aphids also infesting the underside of leaves of greater nettle (Urtica dioica).
Winter hosts belong to the genus Prunus (*) , including damson (P. domestica), blackthorn (P. spinosa), bird cherry (P. padus), myrobalan plum (P. cerasifera), peach, P. pisardii, P. serotina.
P. humuli is a migrating species.
6 generations of fundatrigeniae succeed one another on the primary host. The 1st generation develops in 14-18 days. Alatae appear from the 3rd generation and migrate to a summer host. Each individual produces 21 offspring on average.
7-9 generations of apterae develop on the summer host. Each individual gives rise to about 30-80 descendants. Winged gynoparae move back to the winter host, males following them. Gynoparae deposit 7-15 nymphs on the underside of leaves. Oviparae emerge in the 2nd half of September, each of them laying 6-12 eggs.
Infestation of winter hosts may continue until July-August. 1st generation nymphs (fundatrices) hatch in March-April when Prunus is in blossom. A 2nd generation (fundatrigeniae) emerges and comprises apterae and the 1st winged migrants. The number of alatae increases after the 3rd generation owing to the deterioration of the nutritive substratum. Migration to hop gardens reaches a climax from mid-May to mid-June.
Exiles multiply on hop until the return migration occurs in the autumn.
Females appear in the 2nd half of September.
Egg-laying takes place in October (after mating) in protected areas, between buds and branches.
Damage to winter hosts is unimportant, the leaves becoming only slightly distorted, or curling downwards if infestations are heavier.
Aphids on summer hosts mostly gather on young and yellow-green leaves. Damaged hop leaves turn yellow, can be easily broken, curl downwards, sometimes withering completely. As the plants develop, aphids feed mainly at the base of bracts and upper parts of the flowers, the cone later becoming brown and atrophied.
Sooty moulds develop on the honeydew, which appears as a shiny and sticky layer on the upper side of leaves; photosynthesis is thus reduced.
Colonization of umbels of hop by P. humuli affects the quantity and the quality of the crop as well as the components necessary to beer brewing, the commercial value being reduced.
HYPPZ on line : Species (scientific name), Pests (common names), Glossary, Crops.