Guy Josens

Impact of three aquatic invasive species on native plants and macroinvertebrates in temperate ponds

Biological plant invasions pose a serious threat to native biodiversity and have received much attention, especially in terrestrial habitats. In freshwater ecosystems impacts of invasive plant species are less studied. We hypothesized an impact on organisms from the water column and from the sediment. We then assessed the impact of three aquatic invasive species on the plants and macroinvertebrates: Hydrocotyle ranunculoides, Ludwigia grandiflora and Myriophyllum aquaticum. Our research on 32 ponds in Belgium indicated that the reduction in the native plant species richness was a common pattern to invasion. However, the magnitude of impacts were species specific. A strong negative relationship to invasive species cover was found, with submerged vegetation the most vulnerable to the invasion. Invertebrate richness, diversity and abundance were measured in sediments of invaded and uninvaded ponds along a gradient of H. ranunculoides, L. grandiflora, and M. aquaticum species cover. We found a strong negative relationship between invasive species cover and invertebrate abundance, probably due to unsuitable conditions of the detritus for invertebrate colonization. Taxonomic compositions of aquatic invertebrate assemblages in invaded ponds differed from uninvaded ponds. Sensitive benthos, such as mayflies were completely absent in invaded ponds. The introduction of H. ranunculoides, L. grandiflora, and M. aquaticum in Belgian ponds has caused significant ecological alterations in the aquatic vegetation and the detritus community of ponds.

Relation between termite numbers and the size of their mounds

This article provides a meta-analysis of quantitative data available in literature regarding the relation between termite numbers and the volume of their mounds for 24 species belonging to 13 genera. The leading question behind this analysis is: “how do the respiratory gas exchanges regulate the size of termite mounds?” This question is answered through the analysis of the log–log regression between the volume of the mound and the number of inhabitants. The most confident data support the hypothesis of a respiratory regulation that can be achieved through a relation between the termite numbers and (1) the volume of their mounds (slope of the regression near 1, Noditermes), (2) the surface of the outer walls of their mounds (slope of the regression near 0.67, Termitinae and Nasutitermes) or (3) a compromise between the surface of the outer walls of their mounds and some linear structures of their nests (slope of the regression between 0.67 and 0.33, Trinervitermes and Macrotermes). The way this is achieved is linked with the architecture of the mound. A confident relation was found between the number of individuals and the epigeal volume of their mounds for 18 species for which the most reliable data were provided. Three more accurate models are proposed for estimating the termite population based on the nest material and architecture and on the size of the termites.

DEVELOPMENT OF ISSORIA LATHONIA (LEPIDOPTERA: NYMPHALIDAE) ON ZINC- ACCUMULATING AND NONACCUMULATING VIOLA SPECIES (VIOLACEAE)

The larvae of Issoria lathonia L. feed in natural conditions on several Viola spp., among which are the zinc-accumulating Viola calaminaria (Gingins) Lej. and the nonmetal-accumulating Viola tricolor L. To examine how I. lathonia caterpillars cope with the naturally high foliar zinc concentration of V. calaminaria, we compared the growth of caterpillars reared on leaves varying in zinc concentration. Larvae were fed in controlled conditions with V. calaminaria and V. tricolor grown on noncontaminated soil (i.e., two low-Zn diets) and with V. calaminaria grown on zinc-enriched soil (i.e., one high-Zn diet). Larvae had a higher growth rate when fed with noncontaminated V. calaminaria compared to zinc-enriched V. calaminaria, suggesting that zinc slows down larval growth. However, larvae consumed more leaves of zinc-enriched V. calaminaria (+45%; estimated from fecal mass) compared with noncontaminated V. calaminaria, suggesting that zinc accumulation would not be advantageous to plants. Caterpillars reared on high-zinc leaves regulate their internal zinc concentration through excretion of highly metal-concentrated feces. When kinetics of growth on both low-zinc diets were compared, it appeared that larval development was faster on noncontaminated V. calaminaria than on V. tricolor. This suggests that more nutrients or less feeding inhibitors in V. calaminaria account for fastest growth. Developmental rates on V. tricolor and on zinc-enriched V. calaminaria were similar, despite the high leaf zinc concentration of the latter species. Together with the abundance of V. calaminaria on calamine soils, this may explain why the largest populations of I. lathonia develop on V. calaminaria in Belgium.

Growth and demography of Cubitermes speciosus mounds (Isoptera, Termitidae)

The growth and demography ofCubitermes speciosus mounds were studied in an equatorial forest ecosystem near Kisangani, Zaïre. The mounds were censused and measured on eight occasions from June 1985 to January 1993 on 25 plots of 100 m2.Mounds were found to grow in two ways: either they were enlarged sporadically, leading to a correlation between age and size; or they were no longer enlarged after a 2-year period of initial growth, which means that both large and small mounds can be old.The number of living mounds was fairly constant: it varied between 112 and 152 ha−1 with an average of 139 ha−1, and about a quarter of them were renewed each year. However, a clear tendency was observed over our 7.5-year observation period: the average size of the mounds increased regularly and was 2.7 times larger in 1993 than in 1985.Monthly birth and death rates were estimated using a model of continuous growth. Life expectancy at the age of 3 months was estimated from a survivorship curve at 3.5 years.

Diterpene composition of defense secretion of four west AfricanTrinervitermes soldiers

The diterpene composition of the defensive secretions of minor and major soldiers is described for four sympatricTrinervitermes from the Ivory Coast. The degree of intra- and interspecific similarity between the secretions is assessed and related to available information on soldier behavior. A significant chemical dimorphism is observed between minor and major soldiers ofT. geminatus andT. togoensis. Both species build extensive foraging trails in the open air. During these excursions, the workers are protected by numerous minor soldiers, but only a few major ones. Internest comparison inT. geminatus suggests that the differences between minor and major soldiers is as large within a nest as between different nests. By, contrast, inT. trinervius andT. oeconomus both types of soldiers produce very similar secretions. The foraging habits of those species are far more cryptic. The first species builds earthen tunnels, and the second one forages in close proximity to its nest under cover of vegetation.

Lenticular mounds in the African savannahs can originate from ancient Macrotermes mounds

AbstractSmall lenticular soil mounds are scattered in several African savannahs. At Lamto, Côte d’Ivoire, most of these lenticular mounds house nests of Odontotermes aff. pauperans which have to date been thought to have built them. However, repeated observations made in 2000 and 2015 supply several arguments in favour of another hypothesis, namely that after a nest of Macrotermes has been abandoned and eroded, it could be colonized by O. aff. pauperans and subsequently maintained, stabilized, by this latter species or possibly recolonized by another Macrotermes society.

Laboratory measurements of consumption and growth in Abax ater

The consumption and growth of Abax ater Villers were measured over the whole life cycle under summer conditions in the laboratory.

Molecular systematics of Simulium squamosum, the vector in the Kinsuka onchocerciasis focus (Kinshasa, Democratic Republic of Congo)

Human onchocerciasis (‘river blindness’) is a vector-borne, anthroponotic disease that is predominantly endemic to sub-Saharan Africa, where about 99% of all cases occur. Its causative agent, the spirurid filaria Onchocerca volvulus, is transmitted by haematophagous Simulium blackflies, mainly by S. damnosum s.l. (Diptera: Simuliidae). Simulium damnosum s.l. comprises a complex of about 50 sibling species, roughly half of which are vectors (Vajime and Gregory, 1990; www.nhm.ac.uk/research-curation/ projects/blackflies). So far, the discrimination and identification of these species have mostly relied on the cytotaxonomic analysis of larval polytene chromosomes, although morphotaxonomic and molecular markers have also been found useful (Krueger, 2006). One of the known vector sibling species is Simulium squamosum. This has a wide distribution in the forest and savannah zones of West and Central Africa and has also been identified from onchocerciasis foci near the River Congo and some of its tributaries (Elsen et al., 1988; Henry and Meredith, 1990) in Kinshasa (Democratic Republic of the Congo) and Brazzaville (Republic of the Congo). Further east can be found a distinct subspecies — S. s. kitetense, from the eastern Democratic Republic of the Congo (Elsen and Post, 1989) — and the related ‘Kagera’ cytoform, on the Ugandan–Tanzanian frontier (Dunbar, 1966). To the north, S. squamosum occurs in Cameroon (Traore-Lamizana et al., 2001; Mustapha et al., 2004) and, represented by the ‘Bioko’ cytoform of the closely related species S. yahense, on the island of Bioko (Post et al., 2003). Other potential vectors of the S. damnosum complex have, however, been identified, by morphology, in and around Kinshasa, namely S. damnosum s.s. and S. sirbanum (Elsen et al., 1988). In addition, several morphospecies were described in former Zaire, most of which, unfortunately, do not have cytological correlates (Fain and Elsen, 1980; Elsen et al., 1983). In their short overview of the onchocerciasis focus at the village of Kinsuka, on the western outskirts of Kinshasa, Henry and Meredith (1990) provided the first and, as yet, only conclusive data on the identity of the local vector, which were based on cytotaxonomy. Until the 1940s, the biting nuisance caused by blackflies in this area was immense and sufficient to trigger some of the first blackfly-control measures ever implemented. Since then, for unknown reasons, the biting-fly population has never reached such a nuisance level. Although the Simulium species causing the biting nuisance 60 or 70 years ago was never identified, Henry and Meredith (1990) unequivocally identified S. squamosum in the Kinshasa region. Certain sex-differentiating features of the Kinshasa flies resembled, however, those of the cytotypes A, B, C, and D that were subsequently described from Cameroon and Nigeria (Traore-Lamizana et al., 2001; Mustapha et al., 2004). The primary goal of the present study was to re-establish the cytotaxonomic background for the Kinsuka population of S. squamosum. In a second step, based on the studies of Annals of Tropical Medicine & Parasitology, Vol. 101, No. 3, 275–279 (2007)

Factors influencing respiration in Abax ater

Respiration of Abax ater Villers was measured in a Gilson differential respirometer under various conditions. The main factors influencing respiration were found to be temperature, food consumption, and locomotor activity. Circadian rhythm played a minor role, and metabolic acclimation was absent under most conditions.