Alessandro Cini

Tracking the invasion of the alien fruit pest Drosophila suzukii in Europe

Biological invasions are a leading threat to native wildlife, human health and food production worldwide. Understanding the invasion history helps identifying introduction pathways and organizing integrated management strategies especially aimed at avoiding multiple reintroductions. We coupled a recently developed spatial analysis (Geographic profiling) with trade flows quantification to identify the most likely spreading centre of a recent invader of Europe, the spotted wing drosophila, Drosophila suzukii. This polyphagous vinegar fly recently colonized western countries, where it is heavily threatening fruit production causing severe economic losses. Characterized by a rapid spread and a huge impact, the invasion of this pest has a few precedents and it is becoming a model in invasion biology and pest management. Thanks to our spatial approach based on data presence of D. suzukii in European countries in the very first years of it spread, we update the current knowledge of a first spread in Spain and Italy, suggesting on the contrary that the South of France may be the most likely spreading centre of D. suzukii in Europe. Estimates of propagule pressure (fresh host fruits importation) support this finding as imports from contaminated South East Asian countries are higher in France than in Spain or Italy. Our study provides a first step in the comprehension of invasion history of this pest species and emphasizes geographic profiling as an efficient technique to track down invaders colonization patterns.

A quantitative threshold for nest-mate recognition in a paper social wasp

Nest-mate recognition is fundamental for protecting social insect colonies from intrusion threats such as predators or social parasites. The aggression of resident females towards intruders is mediated by their cuticular semiochemicals. A positive relation between the amount of cues and responses has been widely assumed and often taken for granted, even though direct tests have not been carried out. This hypothesis has important consequences, since it is the basis for the chemical insignificance strategy, the most common explanation for the reduction in the amount of semiochemicals occurring in many social parasites. Here we used the social wasp Polistes dominulus, a model species in animal communication studies and host of three social parasites, to test this hypothesis. We discovered that different amounts of cuticular hydrocarbons (CHC) of a foreign female evoke quantitatively different behavioural reactions in the resident foundress. The relation between CHC quantity and the elicited response supports the idea that a threshold exists in the chemical recognition system of this species. The chemical insignificance hypothesis thus holds in a host–parasite system of Polistes wasps, even though other explanations should not be discarded.

Cuticular Hydrocarbons Rather Than Peptides Are Responsible for Nestmate Recognition in Polistes dominulus

A colony of social insects is like a fortress where access is allowed only to colony members. The epicuticular mixture of hydrocarbons has been widely reported to be involved in nestmate recognition in insects. However, recent studies have shown that polar compounds (mainly peptides) are also present, mixed with hydrocarbons, on the cuticle of various insects, including the paper wasps of the genus Polistes. As these polar compounds are variable among Polistes species and are perceived by the wasps, this cuticular fraction could also be involved in nestmate recognition. Through MALDI-TOF (Matrix-Assisted Laser Desorption Ionization Time of Flight) mass spectrometry analysis, we assessed, for the first time, the intercolonial variability of the cuticular polar fraction of Polistes dominulus in order to evaluate its reliability as source of nestmate recognition cues. We then tested through behavioral assays the importance of the 2 isolated fractions (apolar and polar) in nestmate recognition by presenting them separately to colonies of P. dominulus. Our results showed that the cuticular polar compounds are not colony specific and they are not used by paper wasps to discriminate nestmates from non-colony members. On the contrary, we confirmed that the isolated cuticular hydrocarbons are the chemical mediators prompting nestmate recognition in paper wasps.

Social parasitism and the molecular basis of phenotypic evolution

Contrasting phenotypes arise from similar genomes through a combination of losses, gains, co-option and modifications of inherited genomic material. Understanding the molecular basis of this phenotypic diversity is a fundamental challenge in modern evolutionary biology. Comparisons of the genes and their expression patterns underlying traits in closely related species offer an unrivaled opportunity to evaluate the extent to which genomic material is reorganized to produce novel traits. Advances in molecular methods now allow us to dissect the molecular machinery underlying phenotypic diversity in almost any organism, from single-celled entities to the most complex vertebrates. Here we discuss how comparisons of social parasites and their free-living hosts may provide unique insights into the molecular basis of phenotypic evolution. Social parasites evolve from a eusocial ancestor and are specialized to exploit the socially acquired resources of their closely-related eusocial host. Molecular comparisons of such species pairs can reveal how genomic material is re-organized in the loss of ancestral traits (i.e., of free-living traits in the parasites) and the gain of new ones (i.e., specialist traits required for a parasitic lifestyle). We define hypotheses on the molecular basis of phenotypes in the evolution of social parasitism and discuss their wider application in our understanding of the molecular basis of phenotypic diversity within the theoretical framework of phenotypic plasticity and shifting reaction norms. Currently there are no data available to test these hypotheses, and so we also provide some proof of concept data using the paper wasp social parasite/host system (Polistes sulcifer—Polistes dominula). This conceptual framework and first empirical data provide a spring-board for directing future genomic analyses on exploiting social parasites as a route to understanding the evolution of phenotypic specialization.

Visual Recognition in Social Wasps

Social recognition, i.e. the ability to recognize and assign individual membership to a particular and relevant class, such as caste, dominance status, gender or colony, shapes the amazing organization of insect societies. Traditionally, it has been assumed that social recognition in social insects is mainly governed by chemicals. However, social insects also share information via many other sensory channels, and it has been recently demonstrated that visual signals can mediate several types of social recognition in some species of social wasps. Primitively social wasps, such as paper wasps of Polistes genus, are suitable models to investigate visual communication because their combs lack of envelops allowing light to produce visual cues, their colonies are small, they have a good vision, they show a remarkable individual within-colony colour variation and, finally, they show an intense social life based on social recognition. In this chapter we reviewed the role of visual cues in social recognition inside and outside social wasp colonies focusing both on the intraspecific and interspecific recognition contexts.

Just phoresy? Reduced lifespan in red palm weevils Rhynchophorus ferrugineus (Coleoptera: Curculionidae) infested by the mite Centrouropoda almerodai (Uroactiniinae: Uropodina)

Abstract Invasive species usually act as carriers of their associated organisms like parasites and symbionts. This phenomenon has also occurred with the recent colonization of the red palm weevil, Rhynchophorus ferrugineus, in the Mediterranean area: this introduced pest is strictly associated with several species of mites (mainly belonging to the suborder Uropodina). In this paper, we document the high rate of infestation of Central and Southern Italian red palm weevil populations by the mite Centrouropoda almerodai. This mite species was found in all five investigated regions and infested the large majority of individuals (from 57 to 95%) by settling preferentially under the first pair of wings. Although this mite–weevil association is usually considered as a phoretic relationship, i.e. without impact on hosts, our study revealed that infested individuals have a significantly reduced lifespan (by one-third) in comparison with those not infested. Our study provides evidences that C. almerodai imposes a cost on its carrier host, at least under laboratory conditions, leading us to believe that the R. ferrugineus–C. almerodai relationship is also not phoretic in the wild.

The chemical basis of host nest detection and chemical integration in a cuckoo paper wasp.

SUMMARY Insect social life is governed by chemicals. A great number of studies have demonstrated that the blend of hydrocarbons present on the cuticle (CHCs) plays a pivotal role in intra- and inter-specific communication. It is not surprising, therefore, that social parasites, specialized in exploiting the costly parental care provided by host workers, exploit the host chemical communication system too. Throughout their life cycle, social parasites intercept and break this CHC-based code. Recently, however, several polar compounds (mainly peptides) have been found in addition to CHCs both on the cuticle and on the comb surface of social insects, and their semiochemical role has been demonstrated in some circumstances. In the present study, we used the paper wasp social parasite–host system Polistes sulcifer (Zimmerman)–Polistes dominulus (Christ) to evaluate the relative importance of the CHCs and polar compounds in two different steps of the host exploitation process: host nest detection by the pre-usurping parasite and parasite chemical integration into the host colony. After separating the polar and apolar fractions of the host nest as well as those of pre- and post-usurpation parasites, we carried out laboratory assays based on the binary choice model. Our results show that nest polar compounds neither are used by the parasite to detect the hosts nest nor play a role in parasite chemical integration into the host colony. In contrast, we demonstrate that CHCs are fundamental in both steps, thus confirming their primary role in social insect life and consequently in social parasite–host interactions.

Computer-aided photographic identification of Rosalia alpina (Coleoptera: Cerambycidae) applied to a mark-recapture study

Assessing the conservation status of protected species needs quantitative population data, generally obtained using Capture‐Mark‐Recapture methods (CMR). The exploitation of natural marking (e.g. individual morphological traits) offers an interesting alternative, based on image analyses, which may result in a less manipulation of protected species compared to the typical artificial marking method. In our 2‐year CMR study, we tested for the first time in the natural setting the feasibility and the application of the computer‐aided photographic identification method of Rosalia alpina using the individual elytral spots as the natural marking. The I3SC software was used for the photographic analysis. Data were collected from populations of two National Parks of central Italy during July–August in 2014 and 2015. We developed a standard procedure in order to optimise the image acquisition in the field and to acquire clear and comparable images, facilitating the I3SC screening process. The results demonstrated that the computer‐aided photographic identification of natural markings can be implemented in a CMR population study of R. alpina. Our image processing approach showed that using only the elytral central spot contours made the tracing contour process less time‐consuming obtaining reliable results. Furthermore, I3SC output scores were used to identify a threshold value for the identification of new individuals or recaptures, facilitating the final identification proposed by operators. Finally, we assessed the possibility of performing the methodology using a Citizen Science approach.

Sterile Rhynchophorus ferrugineus males efficiently impair reproduction while maintaining their sexual competitiveness in a social context

The red palm weevil Rhynchophorus ferrugineus, recently spreading from its native range throughout the world, is one of the most dangerous pests for several palm species. The sterile insect technique (SIT) is a promising environmentally friendly approach for the management of this pest. An essential prerequisite of the SIT is that irradiated males released in nature are as sexually competitive as their wild counterparts. Here we evaluated the potential use of the SIT in red palm weevil males by investigating the sexual competitiveness of gamma-irradiated (Cobalt 60 source, dose 80 Gray) males in the laboratory in a natural-like social context with a balanced sex ratio and by testing their efficacy in impairing female reproduction. Our results showed that irradiation did not affect any of the mating behaviour parameters. However, the male reproductive potential was drastically reduced, as fertility was markedly decreased in females mated with irradiated males. Therefore, an 80 Gray irradiation dose is a promising option for the SIT in the control of the red palm weevil, producing sterile but sexually competitive males when tested in a natural-like mating context.

Social biology of Parischnogaster striatula (Hymenoptera: Stenogastrinae)

The social biology of the wasp Parischnogaster striatula has been studied in Peninsular Malaysia. This species shows the main characteristics of hover wasps (Vespidae, Stenogastrinae) which set them aside from the other social Vespidae. These include the use of an abdominal secretion in brood rearing, the three-phase egg deposition and the presence of only four larval instars. Colonies are invariably small sized and on average 1.92 females on the nests present developed ovaries. Colony life revolves around a dominant female, which has developed ovaries and spends most of her time on the nest. Since visual cues were recently found in two different species of Liostenogaster (Stenogastrinae), we also looked for a possible badge of status in these wasps but with negative results.