Differential susceptibility to variable plant phenology and its role in competition between two insect herbivores on oak

Abstract. 1. The population dynamics of Tortix viridana L. (Lepidoptera: Tortricidae) and Operophtera brumata L. (Lepidoptera: Geometridae) on the pedunculate oak Quercus robur L. are driven by the degree to which larval hatch coincides with oak budburst in spring.
2. Experiments with first instar larvae demonstrate that T. viridana has a much narrower dietary breadth, is less inclined to disperse from closed oak buds, and can resist starvation for longer periods than the polyphagous O.brumata.
3. As a result of its specialist foraging strategy, T. viridana may be less susceptible to mortality associated with colonization of oak in spring than O.brumata. This may explain why T. viridana populations are, on average, higher.
4. These results are discussed in the light of previous work which described the competitive advantage of O. brumata in field cage experiments. Stochastic mortality factors, which drive population change in both species independently of competition, favour T.viridana larvae, and over-ride the competitive superiority of O.brumata.     

Accelerating Strawberry Seed Germination by Fungal Infection

Germination of strawberry seed was accelerated by natural andartificial infections of Ulocladium charatarum and other fungi,including the Arthrinium state of Apiospora montagnei and aCladosporium sp. Germination was variously promoted by fungiboth in light and darkness, on damp filter paper, water andmalt agar plates and on horticultural compost. Germinated seedlingswere apparently undamaged by these infections, although whencultured on malt agar the seedlings were overgrown by the fungus.Several other fungi promoted germination, but three of themlater killed the seedlings. Germination of seed of all threecultivars that were tested was promoted by fungal infectionwhich probably promoted germination by hastening breakdown ofthe seed coat. Strawberry, Fragaria ananassa Duch., germination, fungus