Eur. J. Entomol. 92 (4): 623-631, 1995
Medium term effects of early season defoliation on the colonisation of bird cherry (Prunus padus) by insect herbivores
Severe defoliation of Prunus padus saplings in spring 1987 significantly affected growth and nutrient characteristics for the next five years. Trees that experienced 50% or greater defoliation at age 2 and 3 years were significantly smaller than the controls for up to three years after experimental defoliation had ceased. After five years, trees that had experienced the most severe defoliation were still significantly smaller than those trees that had experienced less severe defoliation regimes. Trees that had experienced high levels of defoliation had significantly higher total leaf nitrogen levels and significantly lower calcium levels two years after defoliation than lightly defoliated trees. Four years after the initial defoliation treatments the situation was reversed, nitrogen levels were higher and calcium levels lower in the controls and lightly defoliated treatments than in the heavily defoliated treatments.
The colonisation of the trees by insect herbivores was significantly affected by the initial defoliation treatments. The number of overwintering eggs of the specialist bird cherry feeding aphid Rhopalosiphum padi were significantly greater on the control and lightly defoliated treatments from 1987-1990. Only in 1991 were egg numbers not significantly different between treatments, and in that year populations overall were extremely low. In addition, damage by mid-season generalist herbivores was significantly lower on those trees that had experienced severe initial defoliation. In all other years bar 1989 and 1991, damage levels were significantly higher on those trees. Colonisation by the other bird cherry specialist, the small ermine moth Yponomeuta evonymellus, did not occur until 1991. All trees colonised were from the severe defoliation treatments. These results are discussed in relation to the probable effects on the population dynamics of the two bird cherry specialists.
Keywords: Herbivory, plant mediated competition, Rhopalosiphum padi, Yponomeuta evonymellus, defoliation, plant growth, foliar nitrogen, Prunus padus
Accepted: February 3, 1995; Published: November 30, 1995