Influence of the egg parasitoidPlatytelenomus busseolae [Hym.: Scelionidae] on the population ofSesamia nonagrioides [Lep.: Noctuidae] in central greece

The egg parasitoid,Platytelenomus busseolae (Gahan) (Hymenoptera: Scelionidae) was recorded from egg masses of the corn stalk borer,Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae) on maize in the area of Istiaea, Central Greece. Natural parasitism was studied during the years 1986, 1987. A total of 3,382 egg masses, containing 205,227 eggs, was collected from corn fields. Parasitized eggs were found from end July to mid-October. In 1986. 76.2% of the egg masses and 42.8% of all eggs were parasitized, while in 1987, respective values were 27.6% and 12.9%. The inferior performance of the parasitoid in 1987 may be due to the unfavorable winter and summer conditions. Parasitism decreased when the host population was at its peak, but it increased again within 1 to 3 weeks. A small percentage of egg masses was completely parasitized (9.5% and 4.7% for the 2 years respectively). In 1987, the sex ratio, ♀♀/♂♂ was 1.5: 1 and 26.2% of the egg masses produced only ♂♂. Mated ♀♀ produced 3 times more ♀♀ than ♂♂. It seems that the parasitoid, under favorable weather conditions, can play a significant role in the control of the corn stalk borer.      

Behaviour in usurpers and late joiners ofPolistes biglumis bimaculatus (Hymenoptera,Vespidae)

Summary During the late pre-emergence phase, a foundress of the paper waspPolistes biglumis bimaculatus may be expelled by a conspecific female from her own nest (usurpation) or, less frequently, joined by another female of the same species (late association). The behaviour of femalePolistes biglumis bimaculatus, when usurping a conspecific colony or joining another foundress, is compared with that of foundresses on non-usurped colonies. The most conspicous difference is the intense abdomen stroking behaviour the usurper performs over the comb surface on the first days after usurpation. As observed in otherPolistes species, once usurpers and joiners arrive on a strange nest they will destroy most of the immature brood of the previous nest owner. Although host workers are not aggressive towards the intruder females, reproductive success of usurpers and joiners is low compared with that of legitimate foundresses. The same behaviours observed on usurped colonies are found in the obligate social parasites ofPolistes. These behaviours are therefore discussed in the context of the evolution of intra- and inter-specific parasitism.     

Variation in pea aphid population development in three different habitats

Abstract.

• 1 Seasonal population growth rates for the pea aphid, Acyrthosiphon pisum Harris, were determined in three different host plant habitats; alfalfa, Medicago sativa (L.), clover, Trifolium pratense (L.), and peas, Pisum sativum (L.); over four years and eight places. It was possible to estimate a common intrinsic rate of increase for each host plant habitat.
• 2 An analysis of the relative influence of temporal, spatial and host plant habitat variation showed that the host plant habitat was most important in determining the growth rates of the populations, both in rate of build-up and decline.
• 3 Patterns of alate production in the three different habitats differed substantially between the annual peas and the two perennial legumes. During the summer, alate production was large and rapid in peas and remained low and constant in clover and alfalfa
• 4 Parasitism was highest in peas. The species composition of parasitoids differed between crops.
• 5 Aphids in annual peas had a higher intrinsic rate of increase and a faster rate of decline than in the two perennial legumes. This explains the presence of both migratory and sedentary forms among pea aphids.

     

Factors regulating predation by first-instar spined assassin bugs [Sinea diadema (Fabricius)] (Hemiptera: Reduviidae)

Selected nutritional and developmental factors regulating the predatory behavior of first-instar spined assassin bugsSinea diadema (Fabricius) (Hemiptera: Reduviidae) were investigated. The longevity of unfed nymphs provided with free water, bean pod sections, or glucose solutions was not significantly greater than that of unfed nymphs which were not provided with a source of water. First-instarS. diadema that were provided with larvae ofEphestia kuehniella Zeller (Lepidoptera: Pyralidae) as prey began feeding 1.9 (±0.9) days after hatching. In contrast, first-instarS. diadema that were provided with conspecifics of the same age did not begin feeding until they were 3.9 (±0.9) days old. These results suggest that the potential nutritional benefits to be gained from feeding equal or outweigh the risk of attacking prey capable of effective self-defense only when nymphs have not fed for 4 days after hatching. Providing the nymphs with water or glucose solutions significantly delayed the onset of conspecific predation. Additional data are presented which demonstrate that first-instarS. diadema are not restrained from preying on siblings by kin recognition.     

A morphological study and hybridization analysis of Caloglossa leprieurii (Ceramiales, Rhodophyta) from Japan, Singapore and Australia

Morphological and hybridization experiments were performed on Caloglossa leprieurii (Montagne) J. Agardh collected from Japan, Singapore and Australia in order to evaluate taxonomic characters of this species. Within C. leprieurii at least four mating groups were recognized from the Indo-Pacific region. These mating groups could be characterized by the blade width at the inter-node and the cell-row numbers on the opposite side derived from the first axial cell at the main axis, though these properties showed a certain variability even in the same plant under both field and culture conditions. The phylogenetic relationship and geographic distribution of the four mating groups are discussed.     

HISTORICAL BIOGEOGRAPHY AND CONTEMPORARY PATTERNS OF MITOCHONDRIAL DNA VARIATION IN WHITE-TAILED DEER FROM THE SOUTHEASTERN UNITED STATES

Mitochondrial DNA (mtDNA) was used to characterize patterns of geographic variation among white-tailed deer (Odocoileus virginianus) populations in the southeastern United States. Fifteen restriction enzymes were employed to survey and map 99 restriction sites in 142 deer from 18 localities in five southeastern states. Phylogenetic analysis revealed three primary groups of haplotypes: (1) southern Florida and the Florida Keys, (2) the remainder of peninsular Florida northward to South Carolina, and (3) the Florida panhandle westward to Mississippi. Geographical heterogeneity in haplotype frequencies suggests that stochastic lineage sorting or isolation by distance are not important determinates of mtDNA differentiation among deer populations. The pattern of mtDNA variation in white-tailed deer is concordant spatially with those observed in unrelated taxa suggesting the common influence of historical biogeographic events. The data (1) support previous hypotheses that relate contemporary patterns of intraspecific phylogeography in northern Florida to the physiogeographic history of the region; and (2) suggest that genetic differentiation in southern Florida may be attributable to episodes of Pleistocene dispersal. Despite potentially high vagility and human intervention, ecological and demographic characteristics of deer have effectively preserved the historical pattern of intraspecific mtDNA differentiation.     

GEOGRAPHIC DISTRIBUTION OF MITOCHONDRIAL DNA VARIANTS AND THE HISTORICAL BIOGEOGRAPHY OF THE SPOTTED SALAMANDER,AMBYSTOMA MACULATUM

I analyzed geographic partitioning of mitochondrial DNA (mtDNA) restriction-site variants in the spotted salamander, Ambystoma maculatum. Two highly divergent and geographically separate genetic lineages were identified that differed by a minimum of 19 restriction sites (6% sequence divergence). One of the lineages has a disjunct distribution with very closely related haplotypes occurring in Missouri, Arkansas, North Carolina, and Virginia. The other lineage is found in Michigan, Illinois, and Alabama. The geographic separation of highly divergent mtDNA haplotypes, a pattern that was predicted based on the sedentary nature of these salamanders, is evidence for long-term barriers to gene flow. In contrast, the large-scale disjunction of very similar haplotypes suggests recent, long-distance gene flow and does not match the phylogeographic expectation for a small terrestrial vertebrate. I explain this potential contradiction in the level of importance assigned to gene flow by a scenario in which historical barriers to gene flow account for the two divergent mtDNA assemblages, but stochastic sorting of ancestral polymorphism is responsible for the large-scale geographic disjunction. Ten of 16 populations collected in the Ozark Highlands were fixed for the same haplotype. I attribute this lack of detectable variation to recent colonization of this area, a hypothesis that is supported by paleoecological data and demonstrates the potential benefits of combining data from paleobotany, geology, and other disciplines to reconstruct the historical biogeography of a species.     

Equiproportional temperature-duration responses and thermal influences on distribution and species switching in the copepods Metadiaptomus meridianus and Tropodiaptomus spectabilis

The temperature-dependence of development was studied in two ecologically divergent freshwater calanoids, Metadiaptomus meridianus (Douwe) and Tropodiaptomus spectabilis (Kiefer). Egg durations were determined between 10 and 35 °C, and food satiated post-embryonic development times between 12 and 32 °C. All responses were basically inverse monotonic functions of temperature, adequately described by Blehrádek's equation. M. meridianus generally developed faster than T. spectabilis. Its egg development was faster at all temperatures, and while its naupliar durations were shorter only up to ± 15 °C, its overall post-embryonic development was more rapid up to ± 24 °C in females and ± 28 °C in males. Relatively speaking, however, T. spectabilis is clearly more warm-adapted than M. meridianus. The respective distributions (warm subtropical lowlands vs cooler uplands) of these copepods in the southern African subcontinent, as well as reversible switches between these species observed in two Natal impoundments are consistent with their contrasting thermal responses, although additional considerations apply in respect of the species alternations. T. spectabilis was replaced by M. meridianus in L. Midmar in spring 1981 and 1989, and in L. Albert Falls in spring 1990. Reciprocal replacements occurred in Midmar in autumn 1984, and in Albert Falls in late summer 1991. Both spring switches in Midmar coincided with cool spring temperatures, although the consequent shifts in growth rate advantage predicted from the measured temperature-duration responses only partly explain the switches in this warm-temperate reservoir. Parasitism of T. spectabilis by an ellobiopsid was observed during both switching events in Midmar, and perhaps augmented the change, although its effects on the host are indeterminate. Both species showed exactly parallel temporal changes in fecundity during the recent switches in both reservoirs, indicating closely similar trophic niches in the adults at least, and mitigating the possibility of trophic influences as determinants of the replacement. A dramatic but inexplicable increase (around 50% at 20 °C) in the development time of T. spectabilis was noted between 1988 and 1990, and perhaps contributed too.The protracted historical dominance of T. spectabilis in thermally suboptimal conditions in Midmar is ascribed to a general competitive superiority presumed from its K-selected attributes, in contrast to the r-selection evident in M. meridianus. This alternation between species with contrasting life styles is of fundamental ecological interest. Studies on Albert Falls, commenced in 1989, suggest an even greater competitive superiority of T. spectabilis, in keeping with the warmer conditions in this larger sister reservoir below Midmar.     

Intraspecific cleaning behaviour in Cyprinus carpio in aquaria

Intraspecific cleaning behaviour of diseased juvenile Cyprinus carpio L, in experimental tanks in Wuxi, China has been observed and is described.     

The influence of environmental manipulations on inter– and intra–individual variation in food acquisition and growth performance of Arctic charr, Salvelinus alpinus

Repeated measurements of food intake made on juvenile Arctic charr, Salvelinus alpinus , held under different rearing conditions enabled examination of the effects of environmental manipulations on both intra– and inter–individual variations in food intake to be made. This permitted the assessment of the influences of differential food acquisition on individual growth rates and biomass gain. When charr were held in isolation individual fish showed relatively little day–to–day variability in food intake and inter–individual differences in intake were small ('base–fine' values). All fish exhibited positive rates of growth and the overall range was narrow. Nevertheless, there was a highly significant positive correlation between food intake and growth, indicating that those individuals that consumed the greatest quantities of food were also those that had the highest rates of weight gain. The rearing of charr in groups led to increases in both intra– and inter–individual variations in food intake to levels considerably above 'base–line'. This increased variability in food intake was reflected in rates of weight gain being more variable amongst the charr reared in groups, with fish that lost weight often being recorded. Manipulation of the rearing environment had marked influences upon intra–individual variability in food intake, inter–individual differences in food acquisition and rates of weight gain. High stocking densities and exposure of the fish to moderate water currents were most effective in reducing levels of variability to approach those observed under 'base–line' conditions.