This study focuses on the regulation of synchronization between the life cycle of the oligophagous whitefly, Trialeurodes lauri (Signoret), and its evergreen host tree Arbutus andrachne in Mediterranean chaparral. Whitefly infestations vary considerably among trees. The adults of the univoltine (one generation per year) whitefly emerge en masse during April and May and oviposit on the new spring foliage. Following approximately one month of development to the early fourth instar, the nymphs enter nine-month diapauses, terminating in February. This diapause is induced and maintained by the plant and can be experimentally avoided (in the case of developing young nymphs) or terminated (in the case of diapausing fourth instars), if whitefly-bearing branches are severed from the tree and placed in water under laboratory conditions. This study is the first report of a whitefly diapausing through both summer and winter seasons. The role of the host plant in the process is discussed.

We investigated the effect of seasonality on tree phenology in the tropical montane rain forest of southern Ecuador and analysed possible triggering factors. Two hypotheses were tested: (1) Interspecific synchronization of flowering and fruiting phenology is higher at study sites with pronounced rainfall seasonality compared with sites within perhumid forests. (2) Proximate causes for flowering in closely situated seasonal and perhumid sites are either photoperiodicity or climatic factors. Two nearby study sites with contrasting precipitation patterns were selected at the same altitude east and west of the western Cordillera. Eighty trees from 13 species were observed over a 2.5-y period. Three species were common to both study sites. Phenological and climate data were collected and cross-correlated by conducting a time-series analysis. At the perhumid site, very clear annual patterns of phenological behaviour could be observed for most of the selected rain-forest tree species, but with a poor interspecific synchronization. On the nearby seasonal site in contrast, most species showed high synchrony in their phenological behaviour coinciding with the dry season. There is strong evidence that flowering is induced not by one factor alone: we identified photoperiodic control, radiation and precipitation as possible proximate causes for both sites. Our results confirm studies which state that these factors are closely linked to each other in the tropics.

Leafing, flowering and fruiting of the 24 most representative species of trees and shrubs in Sudanian savannas and fallows near Bondoukuy (Burkina Faso) were studied for 2 y (May 1992 to June 1994). The period of defoliation was generally brief, and leaf flushing, flowering and fruiting occurred mostly in the dry season. The phenological behaviour varied nonetheless across species and individuals. A classification taking into account synchrony/asynchrony and duration in foliation, flowering, fruit ripening and seed dispersal phases allowed comparison of species' phenological plasticity. Species were distributed along a scale of increasing plasticity, from trees to shrubs. Along this scale, species of the Leguminosae appeared to be separated from those of the Combretaceae, the latter being generally considered as characterising fallow farming systems. These results provide new evidence about the effect of phylogenetic constraints on the phenological behaviour of the woody species of the Sudanian savannas.

RÉSUMÉ. La feuillaison, la floraison et la fructification des 24 espèces d'arbres et d'arbustes les plus représentatives des jachères et savanes soudaniennes de la région de Bondoukuy (Burkina Faso), ont été étudiées pendant 2 ans (mai 1992 à juin 1994). La défeuillaison est généralement brève et l'émergence des feuilles, la floraison et la fructification se produisent principalement pendant la saison sèche. Les comportements phénologiques varient cependant entre les individus et entre les espèces. Une classification prenant en compte le degré de synchronisme ainsi que la durée de la feuillaison, de la floraison, de la maturation des fruits et de la dispersion des graines a permis de comparer la plasticité phénologique des espèces. Celles-ci sont distribuées selon un gradient de plasticité croissante des arbres aux arbustes. Sur ce gradient les Légumineuses se dissocient des Combrétacées, espèces qui sont par ailleurs généralement considérées comme caractéristiques des jachères. Ces résultats sont une nouvelle illustration de l'effet des contraintes phylogénétiques sur le comportement phénologique des espèces ligneuses des savanes soudaniennes.