Pheromone communication among sexes of the garden cross spider Araneus diadematus

Chemical communication plays a fundamental role in many aspects of an animal’s life from assessing habitat quality to finding mating partners. Behavioural observations show that chemical communication likewise plays an important role in spiders, but the contexts and the substances involved are little explored. Here, we investigate the chemical communication in the garden cross spider Araneus diadematus (Clerck, 1757) between and within the sexes. Using choice trials, we demonstrate that males are attracted to odours of adult females, but not to those of subadult females. Our data further suggest that adult females avoid odours of conspecific adult females, possibly in order to reduce reproductive competition with other females. Cuticle and silk extracts as well as headspace samples of subadult and adult virgin females were analysed via GC–MS. Available candidate compounds for the female sex pheromone were tested via electroantennography on palps (electropalpography) of adult virgin females and on females in behavioural trials. We propose sulcatone (6-methyl-5-hepten-2-one) as a candidate substance for the female volatile pheromone and several long-chained alkanes and alcohols as candidates for contact pheromones. Apart from demonstrating that attraction of males to females depends on the latter’s developmental stage, our study suggests that pheromones can also play an important role between females, an aspect that requires further attention.

On the Biological Regulators of Bloodsucking Blackflies(Diptera:Simuliidae) of Mixed Forests of Belorussian and Ukrainian Woodlands

This article considers the natural regulators of blood-sucking Simuliidae subzone of mixed forests on the territory of Belarus and Ukraine. In the mixed forests, the major regulators of preimaginal phases of bloodsucking blackflies are microsporidia (Polidyspirenia simulii, Polidyspirenia sp., Thelohania fibrata, Amblyospora bracteata, A. varians), fungi and mermithides (Gastromermis boophthorae). Caddisfly larvae (Hydropsyche angustipennis, Neureclipsis bimaculata, Polycentropus flavomaculatus, Cyrnus flavidus, Oligostomis reticulata, Brachycentrus subnubilus and Rhyacophila nubila) and fishes (Scardinius erythrophthalmus, Rutilus rutilus, Carassius carassius, Gobio gobio) significantly reduce the number of blackflies larvae and pupae. Adult blackflies are eaten by spiders (Araneus diadematus) dragonflies, robberflies, wasps, frogs (Rana temporaria and Rana terrestris), and insectivorous birds (Delichon urbicum, Hirundo rustica, Apus apus). Bactolarvicid and BLP-2477 are among the most effective biological products.

Dynamic environments do not appear to constrain spider web building behaviour

Many laboratory experiments demonstrate how orb-web spiders change the architecture of their webs in response to prey, surroundings and wind loading. The overall shape of the web and a range of other web parameters are determined by frame and anchor threads. In the wild, unlike the lab, the anchor threads are attached to branches and leaves that are not stationary but move, which affects the thread tension field. Here we experimentally test the effect of a moving support structure on the construction behaviour and web-parameters of the garden cross spider Araneus diadematus. We found no significant differences in building behaviour between rigid and moving anchors in total time spent and total distance covered nor in the percentage of the total time spent and distance covered to build the three major web components: radials, auxiliary and capture spirals. Moreover, measured key parameters of web-geometry were equally unaffected. These results call for re-evaluation of common understanding of spider webs as thread tensions are often considered to be a major factor guiding the spider during construction and web-operation.

Microbial repellence properties of engineered spider silk coatings prevent biofilm formation of opportunistic bacterial strains

Bacterial infections are well recognised to be one of the most important current public health problems. Inhibiting adhesion of microbes on biomaterials is one approach for preventing inflammation. Coatings made of recombinant spider silk proteins based on the consensus sequence of Araneus diadematus dragline silk fibroin 4 have previously shown microbe-repellent properties. Concerning silicone implants, it has been further shown that spider silk coatings are effective in lowering the risk of capsular fibrosis. Here, microbial repellence tests using four opportunistic infection-related strains revealed additional insights into the microbe-repellent properties of spider silk-coated implants, exemplarily shown for silicone surfaces. Graphic Abstract

Where Have All the Spiders Gone? Observations of a Dramatic Population Density Decline in the Once Very Abundant Garden Spider, Araneus diadematus (Araneae: Araneidae), in the Swiss Midland

Aerial web-spinning spiders (including large orb-weavers), as a group, depend almost entirely on flying insects as a food source. The recent widespread loss of flying insects across large parts of western Europe, in terms of both diversity and biomass, can therefore be anticipated to have a drastic negative impact on the survival and abundance of this type of spider. To test the putative importance of such a hitherto neglected trophic cascade, a survey of population densities of the European garden spider Araneus diadematus—a large orb-weaving species—was conducted in the late summer of 2019 at twenty sites in the Swiss midland. The data from this survey were compared with published population densities for this species from the previous century. The study verified the above-mentioned hypothesis that this spider’s present-day overall mean population density has declined alarmingly to densities much lower than can be expected from normal population fluctuations (0.7% of the historical values). Review of other available records suggested that this pattern is widespread and not restricted to this region. In conclusion, the decline of this once so abundant spider in the Swiss midland is evidently revealing a bottom-up trophic cascade in response to the widespread loss of flying insect prey in recent decades.

Where have all the spiders gone? Observations of a dramatic population density decline in the once very abundant garden spider, Araneus diadematus (Araneae: Araneidae), in the Swiss midland

Aerial web-spinning spiders (including large orb-weavers) depend, as a group of insectivores, completely on flying insects as a food source. The recent widespread loss of flying insects across large parts of western Europe, both in terms of diversity and biomass, can therefore be anticipated to have a drastic negative impact on survival and abundance of this type of spiders. To test the putative importance of such a to date neglected trophic cascade, a survey of population densities of the European garden spider Araneus diadematus – a large orb-weaving spider – was conducted in late summer 2019 on twenty sites of the Swiss midland. The data from this survey were compared with published population densities for this species from the previous century. The study verifies above-mentioned hypothesis that this spider’s present-day overall mean population density has declined alarmly to densities much lower than can be expected from normal population fluctuations (0.7% of the historical densities). Review of other available records suggests this pattern is widespread and not restricted to this region. In conclusion, the here documented abundance decline of this once so abundant spider in the Swiss midland is evidently revealing a bottom-up trophic cascade in response to the widespread loss of flying insect prey in recent decades.

Urbanization-driven changes in web-building are decoupled from body size in an orb-web spider

In animals, behavioural responses may play an important role in determining population persistence in the face of environmental changes. Body size is a key trait central to many life history traits and behaviours. While behaviours are typically assumed to be highly plastic, size correlations may impose constraints on their adaptive value when size itself is subject to environmental changes.Urbanization is an important human-induced rapid environmental change that imposes multiple selection pressures on both body size and (size-constrained) behaviour. How these combine to shape behavioural responses of urban-dwelling species is unclear.Using web-building, an easily quantifiable behaviour linked to body size, and the garden spider Araneus diadematus as a model, we disentangle direct behavioural responses to urbanization and body size constraints across a network of 63 selected populations differing in urbanization intensity at two spatial scales.Spiders were smaller in highly urbanized sites (local scale only), in line with expectations based on reduced prey biomass availability and the Urban Heat Island effect. The use of multivariate mixed modelling reveals that although web traits and body size are correlated within populations, behavioural responses to urbanization do not appear to be constrained by size: there is no evidence of size-web correlations among populations or among landscapes. Spiders thus altered different components of their web-building behaviours independently in response to urbanization: mesh width and web surface decreased independently with urbanization at the local scale, while web surface also increased with urbanization at the landscape scale. These responses are expected to compensate, at least in part, for reduced prey biomass availability.Our results demonstrate that responses in typically size-dependent behaviours may be decoupled from size changes, thereby allowing fitness maximisation in novel environments. The spatial scale of the behavioural responses to urbanization suggest contributions of both genetic adaptation and plasticity. Although fecundity decreased with local-scale urbanization, Araneus diadematus abundances were remarkably similar across urbanization gradients; behavioural responses thus appear overall successful at the population level.

Diversity and Abundance of Natural Enemies of Helopeltis antonii in Cocoa Plantation Related with Plant Pattern and Insecticide Application

Natural enemy is an important factor in management of cacao pests. One way to increase its diversity and abundance is through agroecosystem management techniques that support. The study was conducted for one year from February 2014 to February 2015 in Banjarsari Plantation and a cocoa farm of Kaliwining Experimental Station, Jember, which applied different cropping patterns and use of insecticides. The purpose of this research was to study the effect of cropping pattern and use of insecticide on diversity and abundance of predators, parasitoids, abundance and intensity of Helopeltis antonii attack. Observation of pests and natural enemies was done visually, using sweep net, yellow pan traps, malaise trap and pifall trap. Intensity of the attack used Pedigo & Buntin equations. Diversity index used Shannon Diversity Index (H’) and Simpson’s dominance index (C). Differences in predator abundance, parasitoid, air temperature, relative humidity, light intensity and rainfall used Wilcoxon test. Results of this study showed that monoculture and intensive use of synthetic insecticides caused lower diversity and abundance of predators and parasitoids, while the abundance and intensity of H. antonii attacks were higher compared with polyculture without insecticide. Banjarsari cocoa plantation that applied monoculture and intensive use of synthetic insecticides, had lower diversity and abundance predators and parasitoids compared with cocoa plantation in Kaliwining that applied polyculture planting without using insecticide. Dominant predators in Banjarsari and in Kaliwining cocoa plantations were Dolichoderus thoracicus and Araneus diadematus, while dominant parasitoid in Banjarsari and in Kaliwining cocoa plantations was Araneus diadematus.