The black bean aphid, Aphis fabae, is polyphagous and its life cycle involves seasonal migration between summer and winter host plants. The aphids are regularly tended by honeydew-collecting ants. This study investigates whether differences exist in honeydew production and honeydew sugar composition for A. fabae subspecies feeding on various host plants and whether such differences reflect differences in the intensity of ant-atttendance (Lasius niger).
A. f. fabae feeding on the perennial summer host, Tanacetum vulgare, produced twice the amount of honeydew (ca. 110 µg per aphid . h-1) than when feeding on the annual host plants Vicia faba or Chenopodium album. Honeydew production of A. f. cirsiiacanthoides feeding on the creeping thistle Cirsium arvense was the highest measured in this study (ca. 150 µg per aphid . h-1). Total sugar concentration in the honeydew of A. f. fabae did not differ when feeding on various summer hosts, whereas the honeydew of A. f. cirsiiacanthoides on C. arvense contained a significantly higher amount of total sugars. The trisaccharide melezitose was the dominant sugar in all the honeydew samples, except for the honeydew of A. f. fabae and A. f. evonymi feeding on the woody winter host plant Evonymus europaeus. The highest proportion of melezitose (80% of total sugars) was found in the honeydew of A. f. cirsiiacanthoides feeding on C. arvense. In this subspecies, the intensity of ant-attendance was also highest. The results confirm our hypothesis, that the sugar richness of the honeydew (rate of honeydew secretion × total sugar concentration) along with the presence of the attractant sugar melezitose are the critical factors in determining the extent of ant-attendance.
In A. f. fabae feeding on the spindle tree E. europaeus, the total sugar concentration of the honeydew as well as the sugar composition differed significantly between generations.
The ladybird Coccinella magnifica is typically considered to be myrmecophilous, and primarily associated with the Formica rufa group of wood ants. It is regularly associated with ants of the F. rufa group in north-western Europe. The very limited data on the habitat preference of C. magnifica in the southern and eastern parts of its range indicate that its ant-associations change and that it may even be non-myrmecophilous in this region. C. magnifica might consist of geographically restricted species or semispecies, on the basis of its geographical variation in ant-association. Laboratory and field observations on north-western myrmecophilous populations C. magnifica appear to indicate it is a generalist predator of aphids. Coccinella magnifica's potential dietary breadth is similar to that of its congener Coccinella septempunctata, which has been used as a model of C. magnifica's non-myrmecophilous ancestor in evolutionary studies.