Growth and development of larvae and galls of Urophora cardui (Diptera, Tephritidae) on Cirsium arvense (Compositae).

The tephritid fly Urophora cardui induces a large multi-chambered gall within the stems of Cirsium arvense. Three distinct phases of gall development have been identified as initiation, growth, and maturation. During initiation the insect gains control of tissue development and during the gall's growth phase parenchyma cells proliferate rapidly surrounding the larvae with thick layers of cells. Patches of primary nutritive cells appear along the surface of larval chambers during the growth phase but few of these cells are consumed. In the gall's maturation phase, thick layers of secondary nutritive cells appear around the surface of larval chambers and the remaining gall parenchyma lignifies. Secondary nutritive cells are the primary food of U. cardui.The gall expands rapidly during the growth phase then abruptly slows at the beginning of the maturation phase. Rate of gall growth is dependent upon the number of larvae per gall but the number of larvae does not affect duration of this phase.Larvae remain in the second instar throughout the growth phase and grow slowly. Once the gall enters the maturation phase and the secondary nutritive cells appear, the larvae moult to the third instar and grow quickly. Larvace attain over 98% of their final weight during the maturation phase and consume all secondary nutritive cells.It is postulated that larvae do not feed extensively on primary nutritive cells since these cells play a key role in gall morphogenesis. The appearance of secondary nutritive cells stimulates larval feeding at a time when gall growth and development is finished.

Accumulation of Cu and Ni in successive stages of Lymantria dispar L. (Lymantriidae, Lepidoptera) near ore smelters at Sudbury, Ontario, Canada.

The accumulation of Cu and Ni in successive life stages of the gypsy moth (Lymantria dispar), feces, and foliage near an ore smelter at Sudbury, Ontario and a control site was investigated. Higher concentrations of Cu and Ni were found in all larval stages collected at Sudbury than in those from the control site indicating that elevated levels of these metals in the Sudbury environment is an important factor influencing body burdens. These differences were associated with higher metal concentrations in the foliage of host trees from this site. However, differences between sites became less significant for pupae and adult stages. At the Sudbury site, concentrations of Cu (microg g(-1) dry wt) decreased in successive instars and then increased in tissues of pupae and adults. In contrast, Cu content (microg/individual) increased during larval development and then decreased in pupae and adults. The pattern of Ni concentration and content in larvae from the Sudbury site was similar to that of Cu. Patterns of Cu and Ni concentration and content throughout the life stages are explained by changes in weight resulting in a dilution effect in early stages, and a concentrating effect in later stages. Differences in Cu and Ni concentration and content between Sudbury and control populations became less significant following the pupal stage suggesting metal elimination with the exuviae and meconium. This study also illustrates the importance of sampling all stages in an insect's development when measuring accumulation of metals. Fecal and foliar concentrations of Cu and Ni from Sudbury were not significantly different suggesting that metal assimilation is low. Even though gypsy moths from Sudbury contain elevated levels of Cu and Ni, metal burdens in their tissues do not represent a significant route through the food chain. However, the conversion of foliage with high metal content to feces implies that other ecosystem consequences should be investigated.

Gall Formation on Cirsium arvense by Ditylenchus dipsaci.

Ditylenchus dipsaci was found to cause gall formation on the stems of Cirsium arvense. The galls were characterized by extensive hypertrophy and hyperplasia, differentiation of nutritive tissue, nuclear modification, and a central cavity containing nematodes. These findings emphasize the importance of host response in investigations of host-parasite interactions and suggest that D. dipsaci may be evolving a host race by reproductive isolation within the confines of a plant gall.