Maurice Hullé

The significance of the sub-Antarctic Kerguelen Islands for the assessment of the vulnerability of native communities to climate change, alien insect invasions and plant viruses

The suite of environments and anthropogenic modifications of sub-Antarctic islands provide key opportunities to improve our understanding of the potential consequences of climate change and biological species invasions on terrestrial ecosystems. The profound impact of human introduced invasive species on indigenous biota, and the facilitation of establishment as a result of changing thermal conditions, has been well documented on the French sub-Antarctic Kerguelen Islands (South Indian Ocean). The present study provides an overview of the vulnerability of sub-Antarctic terrestrial communities with respect to two interacting factors, namely climate change and alien insects. We present datasets assimilated by our teams on the Kerguelen Islands since 1974, coupled with a review of the literature, to evaluate the mechanism and impact of biological invasions in this region. First, we consider recent climatic trends of the Antarctic region, and its potential influence on the establishment, distribution and abundance of alien insects, using as examples one fly and one beetle species. Second, we consider to what extent limited gene pools may restrict alien species’ colonisations. Finally, we consider the vulnerability of native communities to aliens using the examples of one beetle, one fly, and five aphid species taking into consideration their additional impact as plant virus vectors. We conclude that the evidence assimilated from the sub-Antarctic islands can be applied to more complex temperate continental systems as well as further developing international guidelines to minimise the impact of alien species.

Dynamics of Production of Sexual Forms in Aphids: Theoretical and Experimental Evidence for Adaptive "Coin-Flipping" Plasticity

The best strategy for an organism to deal with unpredictable environmental conditions is a stochastic one, but it is not easy to distinguish it from nonadaptive randomness in phenotype production, and its convincing demonstrations are lacking. Here we describe a new method for detection of adaptive stochastic polyphenism and apply it to the following problem. In fall, each female of the bird cherry–oat aphid, Rhopalosiphum padi, faces a decision either to produce sexuals, which mate and lay cold‐tolerant eggs, or to continue production of cold‐sensitive parthenogenetic females, which potentially yields a higher population growth rate but is risky because a cold winter can kill all of her descendants. Using a simulation model, we show that global investment in sexual reproduction should be proportional to winter severity and that variance in the peak date of production of sexual individuals should depend on climate predictability. Both predictions are validated against standardized trap data on aphid flight accompanied by meteorological data, and the predictions support adaptive phenotypic plasticity.

Aphids in the face of global changes.

Global warming is one of the principal challenges facing insects worldwide. It affects individual species and interactions between species directly through effects on their physiology and indirectly through effects on their habitat. Aphids are particularly sensitive to temperature changes due to certain specific biological features of this group. Effects on individuals have repercussions for aphid diversity and population dynamics. At a pan-European scale, the EXAMINE observation network has provided evidence for an increase in the number of aphid species present over the last 30 years and for earlier spring flights. We review these results and provide a review of the principal effects of global warming on aphid communities.

Spatial autocorrelation as a tool for identifying the geographical patterns of aphid annual abundance

Abstract 1 A spatial autocorrelation analysis was undertaken to investigate the spatial structure of annual abundance for the pest aphid Myzus persicae collected in suction traps distributed across north‐west Europe.

Aphid (Hemiptera: Aphidoidea) diversity in Tunisia in relation to seed potato production

Abstract Winged morphs of aphids were investigated from 2002 to 2004 in 4 Tunisian regions of potato seeds production in order to know the aphid diversity and the potential vectors of Potato Virus Y. This is a very important contribution to the knowledge of aphid fauna in Maghreb. A total of 50,030 aphids were caught using yellow water traps and one suction trap. 130 taxa were identified including 103 species. Ten species are well represented in all regions prospected and typical species were also observed in every region. Some differences in species diversity appeared between regions which are discussed considering weather condition and vegetation.

Aphids of sub-Antarctic Îles Crozet and Kerguelen: species diversity, host range and spatial distribution

The native terrestrial food web of sub-Antarctic islands is dominated by decomposers with rare herbivores and almost no predators. As a consequence of increasing human activities, the number of alien plants and invertebrates species, including phytophagous species, has been dramatically rising on these islands. These repeated introductions seem likely to have a great impact on the ecosystem functioning. This is the first detailed study on species diversity, host range and spatial distribution of aphids on French sub-Antarctic islands. Six cosmopolitan and polyphagous aphid species have been recorded on these islands. Five species have been found in the wild where they colonized native and introduced plants, and one species was confined to a glasshouse. Aphids colonized a littoral band and were limited to below 200 m a.s.l. Their spatial distribution is constrained by host plant distribution and temperature. The two dominant species, Myzus ascalonicus and Rhopalosiphum padi, are obligately parthenogenetic in these islands and have been observed to be active on plants during winter. The other species are also presumably obligate parthenogens because of the absence of host plants where sexual reproduction can occur. We suggest that polyphagy and parthenogenesis are major biological traits that influence colonization success by aphids in a sub-Antarctic environment.

EF-1α DNA Sequences Indicate Multiple Origins of Introduced Populations of Essigella californica (Hemiptera: Aphididae)

Abstract Aphids in the pine-feeding Nearctic genus Essigella (Sternorrhyncha, Aphididae, Lachninae) have been introduced in Europe, North Africa, Oceania, and South America. Mitochondrial, nuclear, and endosymbiont DNA sequences of 12 introduced populations from three continents confirm they all belong to Essigella californica (Essig, 1909). Intron sequence variation of the nuclear gene EF-1α has revealed the existence of four distinct groups. Group I gathers one population from China, where the species is newly reported, and several from Europe (France and Italy); Group II is represented by one population from Argentina; Group III includes two populations from Southern Australia with one from New Zealand; and Group IV corresponds to five populations from Eastern and South-Eastern Australia. These results indicate that introduced populations of E. californica have at least four source populations. They also show that intron variation of EF-1α can be a method to discriminate populations of asexually reproducing aphids.

Aphids and associated natural enemies on Ile Amsterdam and Ile Saint-Paul, Southern Indian Ocean

Abstract Ile Amsterdam (37°50′S, 77°30′E, 55 km2) and Ile Saint-Paul (38°43′S, 77°31′E, 7 km2) are very isolated volcanic islands which were originally colonized by a few invertebrate fauna and flora. Invasive species richness has then increased along with human activity. A three-year monitoring programme (1997, 2000, 2001) and a summer campaign (2007) allowed species diversity, host plants, abundance and phenology of introduced aphids and natural enemies to be described. Seven cosmopolitan aphid species have been found on Ile Amsterdam (Aulacorthum solani, A. circumflexum, Macrosiphum euphorbiae, Myzus ascalonicus, M. cymbalariae, M. ornatus and Rhopalosiphum padi) and three on Ile Saint-Paul (A. solani, M. cymbalariae and R. padi). On Ile Amsterdam, these aphids were found on 28 host plants (out of 57 sampled plants), mainly introduced species. Phylica arborea was the only native plant much colonized by one aphid species, A. circumflexum. Aphids were mainly present on the base or in this vicinity. One Hymenopteran parasitoid, Aphidius matricariae, and two hyperparasites (Dendrocerus aphidum and Phaenoglyphis villosa), probably introduced along with their host, were collected. Aphid activity is very low during the autumn (March–May) and at a maximum in spring and summer. Their density and diversity decrease with distance from the research station. From these results, the possible impact of aphids on native plants is discussed.

Relative importance of long-term changes in climate and land-use on the phenology and abundance of legume crop specialist and generalist aphids: Global changes affect aphid regional dynamics

Insect populations are prone to respond to global changes through shifts in phenology, distribution and abundance. However, global changes cover several factors such as climate and land‐use, the relative importance of these being largely unknown. Here, we aim at disentangling the effects of climate, land‐use, and geographical drivers on aphid abundance and phenology in France, at a regional scale and over the last 40 years. We used aerial data obtained from suction traps between 1978 and 2015 on five aphid species varying in their degree of specialization to legumes, along with climate, legume crop area and geographical data. Effects of environmental and geographical variables on aphid annual abundance and spring migration dates were analyzed using generalized linear mixed models. We found that within the last four decades, aphids have advanced their spring migration by a month, mostly due to the increase in temperature early in the year, and their abundance decreased by half on average, presumably in response to a combination of factors. The influence of legume crop area decreased with the degree of specialization of the aphid species to such crops. The effect of geographical variation was high even when controlling for environmental variables, suggesting that many other spatially structured processes act on aphid population characteristics. Multifactorial analyses helped to partition the effects of different global change drivers. Climate and land‐use changes have strong effects on aphid populations, with important implications for future agriculture. Additionally, trait‐based response variation could have major consequences at the community scale.

First records of aphid-pathogenic Entomophthorales in the sub-Antarctic archipelagos of Crozet and Kerguelen

Since the 20th century, the sub-Antarctic islands have suffered an increasing number of biological invasions. Despite the large number of publications on this topic, there is a lack of knowledge on parasitism rates of invasive species and on the role of parasites and pathogens to regulate their populations. Six aphid species have been introduced in the archipelagos of Crozet (Île de la Possession, 46° 25’ S–51° 51’ E) and Kerguelen (49° 21’ S–70° 13’ E). Five of these species were found infected by entomopathogenic fungi of the order Entomophthorales. All these fungal species are cosmopolitan. Conidiobolus obscurus and Entomophthora planchoniana were the most frequently observed on Île de la Possession and in Archipel des Kerguelen, respectively. This is the first report of pathogenic fungi of aphids on the sub-Antarctic islands. We discuss these results in the light of our current knowledge of these insect pathogens. Their introduction by aphids surviving on plants during transportation is the most likely hypothesis to explain their presence on these remote islands.