Topic
Exapion
About: Exapion is a research topic. Over the lifetime, 5 publications have been published within this topic receiving 46 citations.
Papers
TL;DR: Reproductive isolation of sympatric populations may result from divergent selection of populations in different environments, and lead to ecological specialisation, and weevil populations may thus have diverged in sympatry.
Abstract: 1. Reproductive isolation of sympatric populations may result from divergent selection of populations in different environments, and lead to ecological specialisation. In Brittany (France), the gorse Ulex europaeus (Fabaceae, Genisteae), may be encountered in sympatry with one of the two other gorse species present: U. gallii and U. minor. A recent study based on morphological identification of seed predators of gorse has shown that two weevil species (Curculionoidea, Apionidae) infest gorse pods at different seasons and have different host ranges: Exapion ulicis infests U. europaeus in spring, whereas E. lemovicinum infests U. gallii and U. minor in autumn. Weevil populations may thus have diverged in sympatry.
2. As morphological identification of weevils is often difficult and some of the characters used may exhibit individual or environmental variation, mitochondrial and nuclear sequences of weevils collected within pods of the three gorse species in 10 populations of Brittany were used to reconstruct their phylogeny.
3. The results reveal that species differentiation based on morphological characters is confirmed by the two molecular data sets, showing that E. ulicis and E. lemovicinum are distinct species, and suggesting the absence of host races. Finally, E. ulicis was able to use U. gallii and U. minor pods in spring in some years in some populations, which appeared to depend on the availability of pods present during its reproductive period.
4. Divergence between E. ulicis and E. lemovicinum may have resulted from temporal isolation of reproductive periods of weevil populations followed by specialisation of insects to host phenology.
14 citations
TL;DR: The effect of pod size, seed abortion rate and host plant patch density on seed infestation rate and the effect of E. fuscirostre oviposition on the host plant, C. scoparius, was analysed.
Abstract: Cytisus scoparius (L) Link (Fabaceae) is a broom species of European origin introduced both accidentally and as an ornamental plant to Australia, New Zealand and America, where it is classified as a noxious invasive species. One of its main seed predators is Exapion (Exapion) fuscirostre (Fabricius), a weevil with a Palearctic distribution and which has been introduced to United States and New Zealand as a biological control agent. Factors influencing the insect's choice of oviposition location are crucial for the plant's reproductive success. We examined E. fuscirostre oviposition on the host plant, C. scoparius, in the European Mediterranean region. We analysed the effect of pod size, seed abortion rate and host plant patch density on seed infestation rate. Oviposition was greater in patches with low-medium plant densities. Oviposition was also negatively related with seed abortion rate per pod and the rate of infestation by other seed-eating insects. Pod dimensions, particularly width, were positively related with E. fuscirostre oviposition.
7 citations
TL;DR: It is found that the main loss was to ovule death (74% of the initial number of ovules), whereas seed predation (more than 90%) killed the majority of the seeds ripened by the plants.
Abstract: :For three years we studied the interaction between Genista versicolor (Fabaceae) and three seed-predator species, one moth (Coleophora brunneosignata; Coleophoridae) and two weevil species (Exapion compactum and Exapion nov sp; Apionidae), to assess the impact of the insects on seed production and the reciprocal effect of the plant reproductive strategies on the insect’s survival Plants experienced three predispersal mortality factors of ovules: early death of ovules, seed abortion and seed predation Each fruit bore an average of 54 ovules, of which 40 ovules died early in their development and 01 aborted Each fruit sets an average of 13 mature seeds Seed predators invariably infested more than 65% of the fruits every year, killing 87% of the seeds ripened by the plants More than 90% of the seeds predators were weevils However, including the other two predispersal mortality factors, we found that the main loss was to ovule death (74% of the initial number of ovules), whereas seed pred
6 citations
TL;DR: There is a close synchrony between the life cycles of the various weevil species and the phenology of their host plants: the weevils reached peak numbers when the respective main food source for their larvae was available, i.e, when the specific host plants began pod formation.
Abstract: In the centre of the Iberian Peninsula, 5 species of seed-eating weevils show different degrees of host specificity inhabiting species of the broom genera Cytisus Linnaeus and Genista (Tournfourt) Almost all of them are confined to one or 2 closely related host species. There are (a) monophagous species: Exapion laufferi (Schilsky 1906), restricted to Genista cinerascens Lange; (b) oligophagous species restricted to one genus: E fuscirostre (Fabricius 1775) to the genus Cytisus, and E putoni (Ch Brisout 1866) to the genus Genista; (c) oligophagous species in a broad sense: E compactum (Desbrochers 1888) and Pachytychius sparsutus (Olivier 1807) exploiting several species of both genera. Species of the broom genera Adenocarpus De Candolle and Retama Rafinesque were not found to be inhabited by seed-eating weevils, perhaps because of the chemical and morphological characteristics of their pods. In accordance with their degree of specialization, there is a close synchrony between the life cycles of the various weevil species and the phenology of their host plants: The weevils reached peak numbers when the respective main food source for their larvae was available, i.e, when the specific host plants began pod formation. The specialization of these weevil species, such as differences in their oviposition sites, ways of entering the seeds as well as the larval feeding positions inside the seed, are strategies to avoid competitors, to foster coexistence, and to enable the optimal explotation of the resource.
6 citations
TL;DR: The phylogenetic relationships inferred from molecular data are similar to the classification system developed by Alonso-Zarazaga and Lyal (1999), with some exceptions within the tribe Oxystomatini, and genera Ceratapion and Exapion.
Abstract: The systematics of the family Apionidae, as well as the superfamily Curculionoidea, is currently in a state of flux. The comparative analyses of COI sequences from our studies shed some light on the systematics of these weevils. To study the relationship among the organisms of the family Apionidae, we determined the COI sequences of representatives of 23 species and 15 genera, i.e., Apion, Betulapion, Catapion, Ceratapion, Cyanapion, Eutrichapion, Exapion, Hemitrichapion, Holotrichapion, Ischnopterapion, Protapion, Pseudoperapion, Psudoprotapion, Pseudostenapion, and Stenopterapion. Then, they were compared with the COI sequences of 19 species and eight genera from GenBank (Aspidapion, Ceratapion, Exapion, Ischnopterapion, Lepidapion, Omphalapion, Oxystoma, and Protapion). The phylogenetic relationships inferred from molecular data are similar to the classification system developed by Alonso-Zarazaga and Lyal (1999), with some exceptions within the tribe Oxystomatini, and genera Ceratapion and Exapion.
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2012 | 2 |
| 2008 | 1 |
| 2000 | 1 |
| 1997 | 1 |