Carlo Polidori

Breaking up the wall: metal-enrichment in Ovipositors, but not in mandibles, co-varies with substrate hardness in gall-wasps and their associates.

The cuticle of certain insect body parts can be hardened by the addition of metals, and because niche separation may require morphological adaptations, inclusion of such metals may be linked to life history traits. Here, we analysed the distribution and enrichment of metals in the mandibles and ovipositors of a large family of gall-inducing wasps (Cynipidae, or Gall-Wasps) (plus one gall-inducing Chalcidoidea), and their associated wasps (gall-parasitoids and gall-inquilines) (Cynipidae, Chalcidoidea and Ichneumonoidea). Both plant types/organs where galls are induced, as well as galls themselves, vary considerably in hardness, thus making this group of wasps an ideal model to test if substrate hardness can predict metal enrichment. Non-galler, parasitic Cynipoidea attacking unconcealed hosts were used as ecological “outgroup”. With varying occurrence and concentration, Zn, Mn and Cu were detected in mandibles and ovipositors of the studied species. Zn tends be exclusively concentrated at the distal parts of the organs, while Mn and Cu showed a linear increase from the proximal to the distal parts of the organs. In general, we found that most of species having metal-enriched ovipositors (independently of metal type and concentration) were gall-invaders. Among gall-inducers, metals in the ovipositors were more likely to be found in species inducing galls in woody plants. Overall, a clear positive effect of substrate hardness on metal concentration was detected for all the three metals. Phylogenetic relationships among species, as suggested by the most recent estimates, seemed to have a weak role in explaining metal variation. On the other hand, no relationships were found between substrate hardness or gall-association type and concentration of metals in mandibles. We suggest that ecological pressures related to oviposition were sufficiently strong to drive changes in ovipositor elemental structure in these gall-associated Hymenoptera.

Development, Preimaginal Phases and Adult Sensillar Equipment in Aganaspis Parasitoids ~Hymenoptera: Figitidae! of Fruit Flies

Aganaspis daci and Aganaspis pelleranoi (Hymenoptera: Figitidae) are important parasitoids of fruit flies. Here we studied, with light and scanning electron microscopy, aspects of their morphology that could help with plans to mass rear and thus contribute to improved pest control (preimaginal phases) and to shed light on parasitoid-pest relationships (sensillar equipment). The two species present a stalked egg, eucoiliform first and second-instar larvae and hymenopteriform third instar and mature larvae. The first instar presents tegumental differentiations in the mesoma and first metasomal segment in A. daci, but not in A. pelleranoi, while unlike other figitids, neither species displays setae in the mesosomal processes. Second and third instar and mature larvae present tegumental differentiations in A. daci, but not in A. pelleranoi. The moniliform (female) and filiform (male) antennae of A. daci and A. pelleranoi harbor seven types of sensilla, four of them (sensilla campaniformia, sensilla coeloconica type II, and two types of sensilla trichoidea) described here for the first time in Cynipoidea. The largest sensilla were the multiporous placoid sensilla, which were smaller and more numerous in A. pelleranoi. Species also differed to some extent in morphology of sensilla coeloconica. Observations on the ovipositor revealed the presence of coeloconic sensilla on Valva I in both species.

Antennal sensillar equipment in closely related predatory wasp species (Hymenoptera: Philanthinae) hunting for different prey types.

Despite its potential value in phylogenetic and ecological studies, the morphology of antennal sensilla has rarely been compared quantitatively within the Apoidea. Here, through a scanning electron microscopy analysis, we provide an inventory of different types of antennal sensilla and compare their morphology across 10 species of predatory wasps (Crabronidae: Philanthinae) including species that hunt exclusively either on beetles or on bees to feed their larvae. A sensilla-free area was found on the apical flagellomer of all but two species, and its shape and size appear to be useful for separating Philanthini from Cercerini within the subfamily. A total of eight types of sensilla (sensilla placoidea, sensilla basiconica, two types of pit organs, sensilla coelocapitula and three types of sensilla trichoidea) were found in all species, and an additional rarer type (grooved peg sensilla) was found only in three bee-hunting species and for first time in the genus Cerceris. Certain morphological features confirmed the separation of the apoid wasps from the rest of the Apoidea (i.e., bees). A cluster analysis based on the sizes of the different types of sensilla suggested that, overall, sensilla morphology is not a useful taxonomic tool, and thus, other factors likely determine interspecific variability. One candidate factor is the prey type, given some differences in the presence, density, size and distribution of certain types of olfactory sensilla between beetle-hunters and bee-hunters. This hypothesis needs to be further tested quantitatively using a larger species set, more individuals per species, additional sensilla features, and a correction for phylogeny.

Diverse filters to sense: great variability of antennal morphology and sensillar equipment in gall-wasps (Hymenoptera: Cynipidae).

Comparative studies on antennal sensillar equipment in insects are largely lacking, despite their potential to provide insights into both ecological and phylogenetic relationships. Here we present the first comparative study on antennal morphology and sensillar equipment in female Cynipoidea (Hymenoptera), a large and diverse group of wasps, with special reference to the so-called gall-wasps (Cynipidae). A SEM analysis was conducted on 51 species from all extant cynipoid families and all cynipid tribes, and spanning all known life-histories in the superfamily (gall-inducers, gall-inquilines, and non-gall associated parasitoids). The generally filiform, rarely clavate, antennal flagellum of Cynipoidea harbours overall 12 types of sensilla: s. placoidea (SP), two types of s. coeloconica (SCo-A, SCo-B), s. campaniformia (SCa), s. basiconica (SB), five types of s. trichoidea (ST-A, B, C, D, E), large disc sensilla (LDS) and large volcano sensilla (LVS). We found a great variability in sensillar equipment both among and within lineages. However, few traits seem to be unique to specific cynipid tribes. Paraulacini are, for example, distinctive in having apical LVS; Pediaspidini are unique in having ≥3 rows of SP, each including 6–8 sensilla per flagellomere, and up to 7 SCo-A in a single flagellomere; Eschatocerini have by far the largest SCo-A. Overall, our data preliminarily suggest a tendency to decreased numbers of SP rows per flagellomere and increased relative size of SCo-A during cynipoid evolution. Furthermore, SCo-A size seems to be higher in species inducing galls in trees than in those inducing galls in herbs. On the other hand, ST seem to be more abundant on the antennae of herb-gallers than wood-gallers. The antennal morphology and sensillar equipment in Cynipoidea are the complex results of different interacting pressures that need further investigations to be clarified.

Hidden in taxonomy: Batesian mimicry by a syrphid fly towards a Patagonian bumblebee

Batesian mimicry has been repeatedly reported in syrphid flies (Diptera: Syrphidae), with noxious Hymenoptera identified as the models, including bumblebees (Hymenoptera: Aculeata). Despite the number of detailed studies of bumblebee mimics from the Holarctic, only minimal biological and ecological information is available for the same phenomenon in most other biogeographical regions. Here, we analyse in detail a case of Batesian mimicry by the syrphid fly Aneriophora aureorufa Philippi towards the bumblebee Bombus dahlbomii Guérin from Patagonia, a relationship only briefly noted previously in taxonomic studies. A. aureorufa possesses strikingly similar red tawny colouration to the highly hairy body of its model, and somewhat resembles it also in size. Cluster analysis suggests that the mimicry is more pronounced towards larger rather than smaller bumblebee workers. The mimicry is visually very good, but there was no evidence of a behavioural component. Foraging activity of both species seems to be largely restricted to the endemic plant Eucryphia cordifolia. The time spent on flowers was much higher in syrphid flies than in B. dahlbomii and other pollinators, and the time spent between flower visits largely overlapped between all the tested species. The endemic distribution, the apparent plant specialisation, and the invasion of alien bumblebees, make B. dahlbomii and A. aureorufa potentially threatened in some parts of the austral American forests, a priority conservation area.

Food load manipulation ability shapes flight morphology in females of central-place foraging Hymenoptera

BackgroundEcological constraints related to foraging are expected to affect the evolution of morphological traits relevant to food capture, manipulation and transport. Females of central-place foraging Hymenoptera vary in their food load manipulation ability. Bees and social wasps modulate the amount of food taken per foraging trip (in terms of e.g. number of pollen grains or parts of prey), while solitary wasps carry exclusively entire prey items. We hypothesized that the foraging constraints acting on females of the latter species, imposed by the upper limit to the load size they are able to transport in flight, should promote the evolution of a greater load-lifting capacity and manoeuvrability, specifically in terms of greater flight muscle to body mass ratio and lower wing loading.ResultsOur comparative study of 28 species confirms that, accounting for shared ancestry, female flight muscle ratio was significantly higher and wing loading lower in species taking entire prey compared to those that are able to modulate load size. Body mass had no effect on flight muscle ratio, though it strongly and negatively co-varied with wing loading. Across species, flight muscle ratio and wing loading were negatively correlated, suggesting coevolution of these traits.ConclusionsNatural selection has led to the coevolution of resource load manipulation ability and morphological traits affecting flying ability with additional loads in females of central-place foraging Hymenoptera. Release from load-carrying constraints related to foraging, which took place with the evolution of food load manipulation ability, has selected against the maintenance of a powerful flight apparatus. This could be the case since investment in flight muscles may have to be traded against other life-history traits, such as reproductive investment.

Galls of the Temperate Forest of Southern South America: Argentina and Chile

South American temperate forests are of special conservation concern due to their highly endemic flora and fauna, and the occurrence of unique plant-animal interactions. Yet, knowledge regarding gall inducers diversity is limited although increasing rapidly in the last two decades. Here, we performed a review of the literature, supplemented with field collected data by the authors, in order to provide the most up to date knowledge of gall inducers’ diversity associated with native woody species of the temperate forest of Chile and Argentina. We present data for 90 morphospecies of galls associated with 39 host-plant species (21 genera, 15 families), spanning insects and arachnids of at least 6 orders and nematodes. Most of this richness is associated to the best surveyed host-plant genus, Nothofagus, with up to 43 morphospecies of galls in just 8 dominant tree species. Moreover, we provide evidence that gall species richness across all woody host-plant species decreases with elevation, probably driven by decreased temperature and number of available host-plant species. However, this overall trend vary among host plant species and scales of observation. Overall, the study of gall diversity and the biotic and abiotic factors that shape their distribution in these austral forests offer an exciting and fertile field for future research. Besides emphasizing the need for more in depth taxonomic and diversity studies of the gall fauna of these forests, we propose several future lines of research that promise to further elucidate our understanding of the evolution of plant-gall interactions in these forests.

Stridulatory organ and distress call in males and females of a small velvet ant (Hymenoptera: Mutillidae)

Stridulation patterns and stridulatory organ were rarely investigated in the parasitoid family Mutillidae, and data still lack for any sex or species in many subfamilies. We described the morphology of stridulatory organ and the distress call of Myrmilla capitata (Myrmillinae), a small mutillid wasp in which both sexes are apterous. As in other mutillids, the stridulation is produced by rubbing a scraper on the gaster tergite II against a file on gaster tergite III and consists of sequences of pulse trains organized in two subunits (disyllabic chirps) characterized by pulses with opposite phase. Overall, sexes differed in few morphological and acoustical traits. In particular, females had wider and longer files (due to the larger tergite III), smaller ridge thickness, greater inter-ridge distance and produced sound with lower maximum frequencies. This is in accordance to the fact that individuals with wider files, and files with thicker and more separated ridges, tend to emit sounds reaching lower frequencies. Both sexes, on average, seemed to “use” about 50% of the ridges while stridulating, and the file is moved against the scraper with an average speed of about 6 mm/s. Syllable duration and pulse rate (number of pulses/s) were also affected by some morphological traits of the file. Thus, intra-specific variation in the morphology of the stridulatory organ affects stridulation features in this small velvet ant with relatively weak sexual dimorphism.

Morphological distance and inter-nest distance account for intra-specific prey overlap in digger wasps (Hymenoptera: Crabronidae)

Although inter-individual diet variation is common in predatory wasp populations, the factors accounting for such variation are still largely unknown. Here, we asked if paired diet dissimilarity in three species of digger wasps correlates with morphological distance and inter-nest distance, two factors previously linked to diet partitioning in vertebrates. Results sharply differed among species and generations. All sampled populations showed significant inter-individual diet variation for prey taxa, but only in half of the cases for prey size. In one generation of two species [Bembix zonata Klug and Stizus continuus (Klug)], similar-sized wasps had similar prey taxonomic spectra (and for S. continuus also similar prey size spectra), a phenomenon which probably reduces intra-specific competition. In addition, B. zonata females nesting closer to each other had more similar prey taxonomic spectra, suggesting that distant females probably hunt on different patches that harbour different prey species. For the females of a further species (Bembix merceti Parker), pairwise size difference and inter-nest distance did not affect prey dissimilarity. Both morphological distance and inter-nest distance are potentially important in shaping the overlap of individual resource use in wasps, though probably only in certain conditions such as a highly clumped distribution of nests and size-related constraints on prey selection.

Scramble competition by males of the velvet ant Nemka viduata (Hymenoptera: Mutillidae)

The mating systems of mutillid wasps have rarely been studied. Here we present information on the mating system of Nemka viduata. At a site in southern Spain, many males of this species were seen flying over host (digger wasp) nest aggregations while searching for females. Male activity was greatest in the early morning and late afternoon, when females were more active searching for hosts, and on days when relatively large numbers of females were active. Males were not territorial but instead attempted to find emerging females before their competitors. As many as six males might arrive at a receptive female more or less simultaneously. Struggles to control access to females continued until one male copulated with the female on the ground or carried it off in flight to a location away from rival males. Male size seems to affect the patrolling behaviour (number of patrolled sites), but there is little evidence of an advantage for larger males, as expected in a scramble competition mating system. Scramble competition mating systems often evolve in species in which large numbers of males compete for scarce receptive females, a factor that makes male territorial defence of large areas highly costly.