Antoine Foucart

Genetic variation for parental effects on the propensity to gregarise in Locusta migratoria.

BackgroundEnvironmental parental effects can have important ecological and evolutionary consequences, yet little is known about genetic variation among populations in the plastic responses of offspring phenotypes to parental environmental conditions. This type of variation may lead to rapid phenotypic divergence among populations and facilitate speciation. With respect to density-dependent phenotypic plasticity, locust species (Orthoptera: family Acrididae), exhibit spectacular developmental and behavioural shifts in response to population density, called phase change. Given the significance of phase change in locust outbreaks and control, its triggering processes have been widely investigated. Whereas crowding within the lifetime of both offspring and parents has emerged as a primary causal factor of phase change, less is known about intraspecific genetic variation in the expression of phase change, and in particular in response to the parental environment. We conducted a laboratory experiment that explicitly controlled for the environmental effects of parental rearing density. This design enabled us to compare the parental effects on offspring expression of phase-related traits between two naturally-occurring, genetically distinct populations of Locusta migratoria that differed in their historical patterns of high population density outbreak events.ResultsWe found that locusts from a historically outbreaking population of L. migratoria expressed parentally-inherited density-dependent phase changes to a greater degree than those from a historically non-outbreaking population.ConclusionBecause locusts from both populations were raised in a common environment during our experiment, a genetically-based process must be responsible for the observed variation in the propensity to express phase change. This result emphasizes the importance of genetic factors in the expression of phase traits and calls for further investigations on density-dependent parental effects in locust phase change. More population samples with different outbreak histories need to be analyzed to demonstrate that differences in propensity to gregarise evolve because of different outbreak histories.

Low West Nile virus circulation in wild birds in an area of recurring outbreaks in Southern France.

West Nile virus (WNV) has a history of irregular but recurrent epizootics in countries of Mediterranean and of Central and Eastern Europe. We have investigated the temporal enzootic activity of WNV in free-ranging birds over a 3-year period in an area with sporadic occurrences of WNV outbreaks in Southern France. We conducted an intensive serologic survey on several wild bird populations (>4000 serum samples collected from 3300 birds) selected as potential indicators of the WNV circulation. WNV antibodies were detected by seroneutralization and/or plaque reduction neutralization in house sparrows, black-billed magpies, and scops owls, but these species appeared to be insufficient indicators of WNV circulation. Overall seroprevalence was low (<1%), including in birds that had been potentially exposed to the virus during recent outbreaks. However, the detection of a seroconversion in one bird, as well as the detection of seropositive birds in all years of our monitoring, including juveniles, indicate a constant annual circulation of WNV at a low level, including in years without any detectable emergence of WN fever in horses or humans.

The use of Metarhizium anisopliae var. acridum against the grasshopper Rhammatocerus schistocercoides in Brazil

Abstract The control of grasshoppers in Brazil has been based exclusively on chemical insecticides (fenitrothion and malathion). However, as these products are known to be harmful to the environment, their massive use has caused concerns. In the face of pressure against their use, the development of alternative methods became imperative. Some species of entomopathogenic fungi can supplement or even replace chemical insecticides in the control of grasshoppers. An integrated research project began in Brazil in 1993 with the specific objective of developing bioinsecticides based on entomopathogenic microorganisms, especially fungi, to control grasshoppers. Activities centered in surveys, characterization, production, formulation, and field evaluation. Emphasis was given to developing the fungus Metarhizium anisopliae var. acridum as the most promising biocontrol candidate. It is now known that this pathogen can be used efficiently in the control of Rhammatocerus schistocercoides in Brazil and we are verifying its effects on non-target organisms, including other Orthoptera, Diptera and Hymenoptera.

Major threats to a protected grasshopper, Prionotropis hystrix rhodanica (Orthoptera, Pamphagidae, Akicerinae), endemic to southern France

Prionotropis hystrix rhodanica Uvarov, 1923 is a protected grasshopper, endemic to the Crau plain area (a few thousand square kilometres), in southern France. It is restricted to a specific and very characteristic type of vegetation, locally called ‘coussou’.This biotope is currently being increasingly fragmented. This subspecies could disappear in a few years as a consequence of the increase in agricultural areas and of industrial parks. It is necessary to adopt measures rapidly for ameliorating the loss of this biotope. It is of prime importance to stop the increase of new agricultural or industrial areas, to create nature reserves for maintaining areas of natural ‘coussou’, particularly large fragments (more than 1000 ha) and to implement cultivated land remediation. Areas that are too small, too disturbed or too isolated will not be sufficient to ensure the survival of this brachypterous, highly sedentary and vulnerable grasshopper.

Genetic survey of two endangered grasshopper subspecies, Prionotropis hystrix rhodanica and Prionotropis hystrix azami (Orthoptera, Pamphagidae): within- and between-population dynamics at the regional scale

The fragmentation and destruction of natural habitats is one of the major causes of extinction of wild flora and fauna due to human activities. The area around the Mediterranean Basin is particularly affected: this region is one of the world’s richest in terms of biodiversity and is undergoing substantial modification due to extensive changes in land use. We investigated the demographic state (through a genetic survey) of an endangered grasshopper, the geographical distribution of which is restricted to arid open land or glades in south-eastern France. We compared two subspecies: one is severely threatened by the fragmentation of its specific and restricted habitat (Prionotropis hystrix rhodanica in the ‘Crau’ steppe) whereas the other, P.␣h.␣azami, occurs more widely in glades or clearings in the evergreen Mediterranean forest. Genetic diversity at eight microsatellite loci was highly structured, indicating substantial isolation of populations. Within-population diversity was high at all but one site. Genetic drift was the major force involved in this genetic structure, with very little gene flow at the regional scale of observation, consistent with both the limited dispersal of this flightless species and the patchy configuration of its habitat. No significant differences in the extent of genetic diversity or population dynamics were observed between the two subspecies. The observed genetic pattern calls into question the validity of the subspecies status, and shows no strong impact of recent anthropogenic modification of the Crau steppe. The evolution of the Mediterranean xeric and open habitats under both natural and anthropogenic processes is discussed.

Genetic and Morphological Variation in Non-Polyphenic Southern African Populations of the Desert Locust

This study addresses geographic variation of body size and shape and of allele frequencies at 21 microsatellite loci in southern African populations of the desert locust, Schistocerca gregaria. These populations, which belong to the subspecies S. g. flaviventris, lack the capacity to change phase and to swarm relative to the northern populations of the nominate subspecies, S. g. gregaria. We reported overall genetic and morphological similarities among localities that cover most of the subspecies range. Of particular interest, the level of genetic diversity was moderately lower than in the swarming subspecies of the northern range. In addition, S. g. flaviventris populations were genetically homogeneous, such as observed in the northern range of the nominate subspecies. This result can be explained by north—southwest seasonal migration to follow rainfall.

Multiplex PCR assay to discriminate four neighbouring species of the Calliptamus genus (Orthoptera: Acrididae) from France.

Definition of the genus Calliptamus (Orthoptera: Acrididae) has generated many taxonomic debates. Even now, the existence of different geographical morphs hinders species determination, particularly as concerns females and larvae. Some of these species are observed in southern France and are recognized as potential pests. To circumvent problems of species identification in ecological surveys, we developed a single multiplex PCR method based on mitochondrial Cytochrome Oxydase I diagnostic polymorphisms to differentiate between the four species, Calliptamus italicus, C. wattenwylianus, C. siciliae and C. barbarus, in southern regions of France.

Climate‐driven geographic distribution of the desert locust during recession periods: Subspecies’ niche differentiation and relative risks under scenarios of climate change

The desert locust is an agricultural pest that is able to switch from a harmless solitarious stage, during recession periods, to swarms of gregarious individuals that disperse long distances and affect areas from western Africa to India during outbreak periods. Large outbreaks have been recorded through centuries, and the Food and Agriculture Organization keeps a long-term, large-scale monitoring survey database in the area. However, there is also a much less known subspecies that occupies a limited area in Southern Africa. We used large-scale climatic and occurrence data of the solitarious phase of each subspecies during recession periods to understand whether both subspecies climatic niches differ from each other, what is the current potential geographical distribution of each subspecies, and how climate change is likely to shift their potential distribution with respect to current conditions. We evaluated whether subspecies are significantly specialized along available climate gradients by using null models of background climatic differences within and between southern and northern ranges and applying niche similarity and niche equivalency tests. The results point to climatic niche conservatism between the two clades. We complemented this analysis with species distribution modeling to characterize current solitarious distributions and forecast potential recession range shifts under two extreme climate change scenarios at the 2050 and 2090 time horizon. Projections suggest that, at a global scale, the northern clade could contract its solitarious recession range, while the southern clade is likely to expand its recession range. However, local expansions were also predicted in the northern clade, in particular in southern and northern margins of the current geographical distribution. In conclusion, monitoring and management practices should remain in place in northern Africa, while in Southern Africa the potential for the subspecies to pose a threat in the future should be investigated more closely.

Subspecific taxonomy of the desert locust, #Schistocerca gregaria# (Orthoptera: Acrididae), based on molecular and morphological characters

We evaluated the validity of the subspecific designation for Schistocerca gregaria gregaria (Forskål) and Schistocerca gregaria flaviventris (Burmeister), isolated in distinct regions along the north–south axis of Africa. Towards this goal, we assessed the variation of multiple morphological and molecular traits within species. We first used elliptic Fourier and landmark‐based relative warps analyses to compare the size and shape of two internal and two external structures of male genitalia. We provide a discriminant function which classified the specimens with 100% accuracy and selected shape elements of the external structures only (cercus and epiproct). We also tested eight molecular markers, and because of either absence of variation or contamination by mitochondrial DNA (mtDNA)‐like sequences, we used a clone‐and‐sequence analysis of the standard cytochrome c oxidase subunit I mitochondrial DNA barcode only. We differentiated 185 true mitochondrial sequences from 66 mitochondrial DNA‐like sequences, most of which were from S. g. gregaria specimens. On the dataset of mitochondrial origin, we identified three characteristic point mutations that diagnosed the two allopatric subspecies with 94% accuracy. Minimum spanning network and parsimony tree analyses identified S. g. flaviventris as a monophyletic lineage distinct from the nominate subspecies. Accordingly, microsatellite data indicate rarely occurring admixture events only, showing that independent evolutionary history is the norm.

Parental crowding influences life-history traits in Locusta migratoria females

Parental environments could play an important role in controlling insect outbreaks, provided they influence changes in physiological, developmental or behavioural life-history traits related to fluctuations in population density. However, the potential implication of parental influence in density-related changes in life-history traits remains unclear in many insects that exhibit fluctuating population dynamics, particularly locusts. In this study, we report a laboratory experiment, which enabled us to characterize the life-history trait modifications induced by parental crowding of female individuals from a frequently outbreaking population of Locusta migratoria (Linnaeus) (Orthoptera: Acrididae). We found that a rearing history of crowding led to reduced female oviposition times and increased offspring size but did not affect the developmental time, survival, fecundity, and the sex-ratio and the number of offspring. Because all studied females were raised in a common environment (isolation conditions), these observed reproductive differences are due to trans-generational effects induced by density. We discuss the ecological and evolutionary implications of the observed density-dependent parental effects on the life-history of L. migratoria.