摘要:

Abstract.1. Populations of creosote bush (Larrea tridentata(DC) Coville), were studied in Arizona to determine whether associated gallformers (Cecidomyiidae:Asphondyliaspp.) were more abundant on water‐stressed or nonstressed plants. Gall densities were measured along a steep elevational gradient that extended from mesic, higher elevations to lower elevations in the desert; and in the Grand Canyon where severely water‐stressed and relatively unstressed plants occurred adjacently. At the Grand Canyon site, the responses of creosote bush to water stress were also studied.2. The number and densities ofAsphondyliaspecies increased both at lower elevations and locally on water‐stressed plants in the Grand Canyon, indicating that climatic and local conditions influence gallformer abundance in the same way.3. Five of the eightAsphondyliaspecies studied at the Grand Canyon site were more abundant on stressed plants, two species were more abundant on nonstressed plants and one species showed no preference for either plant type.4. Densities of most species on stressed plants were positively correlated with the number of meristematic terminals per branch, which were more numerous on stressed plants, due to a bushier architecture. Flower gallformers were more abundant on nonstressed plants, which produced more flowers. Gall densities did not correlate with chemistry measurements, although these parameters also varied with level of stress.5. These results suggest that gallforming species respond variably to plant stress, even within a closely‐related lineage, and that there are effects of stress on plants, including architectural changes, that may be more important to herbivores than biochemical effects emphasized by White (1984) and

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00787.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. The leaf‐cutting antAtta cephalotes(L.) in a Costa Rican tropical moist forest showed diel changes in foraging activity. In most colonies studied, foraging was primarily nocturnal, although in a few colonies it was primarily diurnal.2. In all colonies studied, mean forager mass was larger at night than during the day.3. At night, most foragers carried freshly cut leaf fragments, whereas during the day a large proportion carried dried fragments and other vegetable matter collected from along their trail.4. Along one trail, where foraging was primarily nocturnal, the match between ant mass and load mass was compared for laden ants at night and during the day. Laden ants at night were larger, carried relatively heavier loads, and showed a higher degree of matching between their mass and load mass than those foraging during the day.5. A comparison of load masses of ants coming down a local tree and of ants picking up marked fragments from along their trail suggested that the diel difference in load mass and in the match between ant mass and load mass were related to the greater proportion of ants carrying freshly cut leaf fragments at night. Fresh fragments weighed more due to higher water content, and the match between ant mass and load mass was greater for ants cutting fresh fragments than for ants picking up abandoned fragments from along their trail.6. Possible explanations for the diel changes in forager size and activity are discusse

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00788.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.1. Polyphagous predator densities were manipulated in a wheat crop using polythene exclusion barriers.2. The rates at which aphids fell to the ground and subsequently climbed and returned to the crop canopy were measured.3. Peak aphid density was highest when polyphagous predator density was lowest.4. Similar rates of aphid fall‐off were measured in each plot, but aphid climbing rate was highest when predator densities were lowest.5. It was concluded that ground‐zone predators reduced the rate at which aphids return to the crop can

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00789.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00790.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0307-6946    

DOI:10.1111/j.1365-2311.1990.tb00791.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY