Development of the sugar beet cyst nematode, Heterodera schachtii, was studied in growth chambers at 20, 25, 29, 32 and 35 ± 1 oC on Beta vulgaris cv. Saccharifera. The optimum temperature for reproduction appeared to be 32 oC, at which the life cycle, from second-stage juvenile (J2) to J2, was completed in 16-19 days; at 35 oC, 20-21 days were required. Juveniles emerged from eggs within 29 da...

Numerous molecular studies have identified morphologically cryptic, freshwater invertebrate species, but have not suggested possible mechanisms for their phenotypic stasis. The amphipod crustacean genus Hyalella contains numerous morphologically cryptic species in the H. azteca complex, as well as a small number of morphologically very divergent, narrowly endemic taxa. One such taxon, Hyalella ...

The mature visual system possesses mechanisms that enable invariant perception of the contrast of an object and its features as the object undergoes changes in distance. This phenomenon, which has been called contrast constancy, obtains at suprathreshold contrasts only. Some models of contrast constancy assume the presence of narrowband spatial-frequency channels. An implication of M.S. Banks, ...