Density Independent Gall Dispersion in a Willow Complex

Abstract

Galls are complex plant-parasite interactions in which plants encapsulate and house the attacker, providing food and shelter space in a structure called a gall (Mani, 1992). Plant galls are common and widespread and can be found on all the different organs of plants (Mani, 1992). The plant grows abnormally at the site where it is wounded by the parasite, forming the gall by its own cell growth (Darlington, 1968). Insects are the most significant cause of plant galls. Despite the diversity of orders of galling insects, 80% of all galling insects belong to just two families, the Cecidomyiidae (Fig.1) and the Cynipidae, galling midges and galling wasps respectively (Hartley, 1992). Adult midges lay eggs on a host plant. Secretions of larval salivary enzymes and physical damage to the plant cells caused by feeding larvae changes the physiology and cytology of the plants. In a dramatic interplay between the plant’s defensive response and the insect’s specialized adaptation, the developing larvae take control of the affected plant cells’ development and proliferation. The affected plant cells then differentiate into tissues which the larvae feed on (Harris, 1994). The mature gall encapsulates the larvae providing food throughout development (Dreger-Jauffret, Mani 1992) The galls that insects cause vary widely in shape and are specific to the insect that causes them. Galling insect parasites are often easier identified by the shape of the galls they induce than by their own physiology. (Resh, Carde, 2003)