What digestive adaptations permit herbivorous nonruminant mammals to sustain much higher metabolic rates than herbivorous lizards, despite gross similarity in digestive anatomy and physiology? We approached this question by comparing four herbivorous species eating the same diet of alfalfa pellets: two lizards (chuckwalla and desert iugana) and two mammals (desert woodrat and laboratory mouse). The mammals had longer small and large intestines, greater intestinal surface area, much higher (by an order of magnitude) food intake normalized to metabolic live mass, and much faster food passage times (a few hours instead of a few days). Among both reptiles and mammals, passage times increase with body size and are longer for herbivores than for carnivores. The herbivorous lizards, despite these much slower passage times, had slightly lower apparent digestive efficiencies than the mammals. At least for chuckwallas, this difference from mammals was not due to differences in body temperature regime. Comparisons of chuckwallas and woodrats in their assimilation of various dietary components showed that the woodrat's main advantage lay in greater assimilation of the dietary fiber fraction. Woodrats achieved greater fiber digestion despite shorter residence time, but possibly because of a larger fermentation chamber, coprophagy, and/or different conditions for microbial fermentation. We conclude with a comparative overview of digestive function in herbivorous lizards and mammals, and with a list of four major unsolved questions.

1. The brown planthopper, Nilaparvata lugens (Stil), is a major pest of rice in Asia. It is known to make wind-assisted migratory flights each year to colonize the summer rice growing areas of China, Japan and Korea.2. Modelling windborne displacements between rice growing areas in Asia requires migratory behaviour and flight duration t o be established for this insect.3. Field and laboratory observations suggest that N.Zugens take-off at dusk and that some continue flying for u p to 24-26 h if the temperature is 2 17°C. 4. Trajectories for 10 ni above ground level and 1.5 km above mean sea level are used to identify possible sources and, hence, to estimate the flight times of Nlugens caught in nets on ships on the East China Sea in 1973 and 1981.5. Estimated flight times between the sources and the ships ranged from about 9 t o 30 h.6. Results suggest that long-distance migration can occur in surface winds, when they are strong, but that long-distance migration is more likely at 1.5 km.7. When simulating windborne displacements of Nlugens, it can be assumed that in areas and a t heights where the temperature is > 17"C, some migrants will fly downwind for up t o 30 h after a dusk take-off. Others will fly for shorter periods, giving the population as a whole the opportunity to colonize all the rice crops flown over.

Radar, aerial netting and ground sampling were used to study the autumn migration of Nilaparvata lugens (Stal) in Jiangsu Province in east central China. Emigration of macropterous adults increased from late August until late September as the main rice crop matured and was harvested. In early and mid September, the resulting windborne migrations carried the planthoppers mainly towards the west, although the migration directions ranged (within the western sector) from south to north. By late September, however, displacements were predominantly to the south-west on the then prevailing north-east monsoon winds: migration was particularly rapid when the north-easterlies were reinforced by typhoons. Although in late September such movements to more southerly latitudes are essential for the survival of the planthoppers' progeny, we found no definite evidence for preferential emigration on winds blowing towards the south. There were, however, indications that when winds towards the north occurred, the duration of migratory flight was curtailed. Irrespective of any possible preference for migration on northerlies, a large proportion of the N. lugens population would normally be carried in an adaptive southwards direction, because the advent of the north-east monsoon occurs at a time when the number of flight-ready planthoppers approaches its peak.

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