Ann Cloarec

Cockroaches as carriers of bacteria in multi-family dwellings

The potential risk of bacterial dissemination due to the presence of cockroaches (Blattella germanica, Blattellidae) in low-income flats was investigated. Cockroaches can carry a great variety of bacterial species; we identified 30 different species from 52 different flats. Klebsiella oxycytoca, K. pneumoniae and Enterobacter cloacae were the most frequently found. Pathogenic and potentially pathogenic bacteria represented 54% of all the bacterial identifications. Bacteria were carried either on the cuticle or in the gut. Contamination through external contact is sufficient to insure bacterial diffusion. There was a very low level of overlap estimated by Piankas index (a) between the bacterial flora of neighbouring blocks of flats, and (b) between bacterial flora of different flats in the same block.

Cuticular extracts inducing aggregation in the German cockroach, Blattella germanica (L.).

German cockroaches Blattella germanica (L.) are gregarious insects. An aggregation pheromone contributes to the maintenance of aggregates. Choice experiments checked the efficiency of different solvents, i.e. dichloromethane, methanol and pentane, in extracting attractive substances and compared the attractiveness of extracts of different parts of the body. Dichloromethane and pentane were the most efficient solvents tested for extracting the attractive substances. Methanol whole body extracts appeared inefficient to induce aggregation. The proportion of larvae attracted to conditioned papers decreased in relation to the size of cuticular surface washed, from whole body to half-body and again to a section of the body cut in three. Attractive substances appear to be present on all parts of the body. Chemical analysis by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) showed that the active extracts contained only cuticular hydrocarbons. In addition to behavioural tests, differences between the composition of methanol extracts and that of the extracts for the other two solvents were revealed by GC. These results indicated that the cuticular hydrocarbons operate as an aggregation pheromone in Blattella germanica.

Bacterial Load of Cockroaches in Relation to Urban-Environment

Sanitation is an important problem in relation to the control of pests in urban environments. This investigation analysed the potential risk related to the presence of cockroaches and their capacity for disseminating bacteria in six different types of buildings: hospital nursing area and out-patient area, swimming-pool pool-side and toilet area, low-income flats and food-handling places. Fifty-six species of bacteria were identified from 157 samples, 14 of these have previously been reported as potentially pathogenic for man and vertebrates. Similarities were found between samples collected in (a) the hospital out-patient area and food-handling establishments and (b) the hospital nursing area and flats. Pool-sides possessed a poorer bacterial flora. There was a greater bacterial specific diversity in food-handling establishments, flats and swimming-bath toilet area. Enterobacter cloacae. Klebsiella pneumoniae and Klebsiella oxytoca were dominant species in flats and the hospital nursing area. Therefore, cockroaches can play a role in disseminating bacteria, which they can carry passively on their cuticle.

Comparative genetic diversity of parasites and their hosts: population structure of an urban cockroach and its haplo-diploid parasite (oxyuroid nematode).

Few studies have investigated the genetic structure of both host and parasite populations at a level of populations and at a level of individuals. We investigated the genetic structure of the urban cockroach Blattella germanica and its oxyuroid parasite Blatticola blattae. Random amplified polymorphic DNA (RAPD) markers were used to quantify genetic diversity between and within four populations (from two cities in France) of the host and its parasite. Diversity based on phenotypic frequencies was calculated for each RAPD marker using Shannon‐Wiener’s index. We used multivariate analyses to test the significance of genetic differentiation between host and parasite populations. Analysis of molecular variance was also used. Both methods gave similar results. Diversity between pairs of individuals was estimated by Nei & Li’s index. Genetic diversity was higher within host or parasite populations (80% and 82%, respectively, of explained diversity) than between host or parasite populations (20% and 18%, respectively, explained diversity). The genetic distances between pairs of parasite populations (or individuals) were not correlated with the genetic distances between the corresponding pairs of host populations (or individuals).

Genetic population structure of the German cockroach, Blattella germanica: Absence of geographical variation

The genetic structure of 31 populations of the German cockroach, Blattella germanica (L.), located in two French cities 900 km apart, was estimated by enzyme gel electrophoresis. A set of 41 loci was analysed. Eight loci (4 Est, 3 Lap and 1 Got) were polymorphic. Diversity was estimated at different geographical levels: the overall population, between cities and within a city. Hierarchical F‐statistics indicated significant genetic differentiation between all populations and among populations within each city, but no differentiation between cities. FST values for populations within each city and for the overall sample were substantially dissimilar. In addition, a cluster analysis did not separate populations according to their geographical origin but according to the predominance of either of the two alternative Est‐4 alleles. The results of this analysis point to the absence of genetic differentiation on a large geographical scale: no large‐scale geographical distance effect was detected. However, we evidenced strong genetic substructuring on a local scale, within cities.

Exploitation of food resources by the cockroach Blattella germanica in an urban habitat

The exploitation of food resources by the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae) was investigated experimentally in relation to distance from shelters and depletion of neighbouring food patches. In addition, the dynamics of exploitation of a patch were analysed. Observations were made after dark in a public swimming baths building and each one lasted 3 h. Food patches were placed in rows, at different distances from the shelters. The number of cockroaches in food dishes, in a 20 cm diameter circle round each food dish and in a 60 cm diameter circle round this first circle were recorded.

Factors influencing the choice of predatory tactics in a water bug, Diplonychus indicus Venk. & Rao (Heteroptera : Belostomatidae)

The tropical water bug Diplonychus indicus is a highly versatile predator that alternates quickly from active foraging to ambushing. The influence of hunger level, the presence of prey and environmental complexity on swimming, diving resting and foraging by adult males was investigated at the individual level, in a factorial experiment with three main treatments. There were simple relationships between these factors and the water bugs behaviour, and interactions between these three factors also affected foraging. The general distribution of foraging tactics between active search and ambushing was significantly influenced by the presence of perching sites (vegetation), but not by hunger levels although hungry bugs as well as bugs in the absence of perching sites were significantly more active than well-fed subjects or bugs in the presence of perching sites. In the presence of vegatation, predatory attempts included fewer dives and more attempts from ambush including preliminary orientations. Hunger level, however, did influence the distribution of ambush predatory tactics; the attempts by hungry subjects included more preliminary orientations. Capture efficiency was not affected by hunger level, but it was affected by the presence of perching sites. Under these experimental conditions the bugs appeared to be capable of modifying, to a certain extent, their predatory tactics in relation to the environment. Nevertheless, the choice of a predatory tactic did not appear to be taken on an all or none basis.

Age-related changes in foraging in the German cockroach (Dictyoptera: Blattellidae)

The dynamics of exploitation of standard experimental food sources by the German cockroach, Blattella germanicaL. (Blattellidae), were analyzed in an urban habitat in relation to developmental stage. The data presented here stress differences in foraging capacities between small (first-and second-instar) larvae and animals of other developmental stages. The first animals to arrive in a food patch presented a developmental-stage distribution significantly different from that of the general population. Adults and large larvae (fifth and sixth instars) were the first to find food sources and, in particular, before small larvae. Significant differences appeared between developmental stages concerning givingup time and the time animals left a patch. Small larvae were significantly underrepresented in a patch just before food exhaustion but they were significantly more numerous than expected just after depletion. Small larvae remained in the vicinity of a depleted food dish longer than animals of other developmental stages. Adults left patches as soon as these were depleted, long before small larvae did. Developmental stage influenced rate of departure. These observations indicate that cockroaches improve their foraging performance as they grow larger.

Variations of foraging tactics in a water bug, Diplonychus indicus

The predatory behaviour ofDiplonychus indicus Venk. & Rao (Heteroptera: Belostomatidae), a tropical water bug, appeared to be highly versatile. Male adultD. indicus alternated from active foraging to ambushing during the same observation. The predatory movements described here were divided into 7 different categories. Five include ambushing and no active search: simple capture, strike, lunge and strikes following a preliminary vertical or horizontal orientation. Two include active search: dive and swimming bout.Success rates of capture varied with predatory movement category and with predatorprey distance. Attempts including lunges had the highest success rate. Attempts including short lunges, small vertical or horizontal turns or short dives were less likely to be successful than attempts including relatively longer lunges, larger vertical or horizontal turns or longer dives.

Development of the compound eyes of the water stick insect, Ranatra linearis

ABSTRACT. Relationships between estimation of predator‐prey distance prior to a capture attempt and some features of the compound eye are investigated at all stages of post‐embryonic development. Interommatidial angles increase gradually from the anterior and the dorsal regions to the posterior and ventral regions. Facet diameters vary only slightly over the eye surface but increase with age. New ommatidia appear around the borders of eye after each moult. The older ommatidia are pushed away from the border. From one instar to another ommatidia change their direction of view from between 10d̀ to 30d̀ relative to the body axes. This change in direction far exceeds the calculated changes in direction that would be optimal if ommatidia were to continue viewing the same relative directions in space. This suggests a high degree of plasticity of the underlying neuronal networks.