Differences In Host Preference Research Articles

Genetic Variation of Anastrepha suspensa (Diptera: Tephritidae) in Florida and the Caribbean Using Microsatellite DNA Markers

Anastrepha suspensa (Loew) (Diptera: Tephritidae), the Caribbean fruit fly, is indigenous to Florida and the Greater Antilles where it causes economic losses in fruit crops, including citrus. Because of the geographic separation of many of its native locations and anecdotal descriptions of regional differences in host preferences, there have been questions about the population structure of A. suspensa. Seven DNA microsatellite markers were used to characterize the population genetic structure of A. suspensa, in Florida and the Caribbean from a variety of hosts, including citrus. We genotyped 729 A. suspensa individuals from Florida, Puerto Rico, Cayman Island, Dominican Republic, and Jamaica. The investigated seven loci displayed from 5 to 19 alleles, with expected heterozygosities ranging from 0.05 to 0.83. There were five unique alleles in Florida and three unique alleles in the Caribbean samples; however, no microsatellite alleles were specific to a single host plant. Genetic diversity was analyzed using F(ST) and analysis of molecular variance and revealed low genetic diversity between Florida and Caribbean samples and also between citrus and noncitrus samples. Analyses using migrate revealed there is continuous gene flow between sampling sites in Florida and the Caribbean and among different hosts. These results support previous comparisons based on the mitochondrial cytochrome oxidase I locus indicating there is no genetic differentiation among locations in Florida and the Caribbean and that there is no separation into host races.

Mining the plant-herbivore interface with a leafmining Drosophila of Arabidopsis.

Experimental infections of Arabidopsis thaliana (Arabidopsis) with genomically characterized plant pathogens such as Pseudomonas syringae have facilitated the dissection of canonical eukaryotic defence pathways and parasite virulence factors. Plants are also attacked by herbivorous insects, and the development of an ecologically relevant genetic model herbivore that feeds on Arabidopsis will enable the parallel dissection of host defence and reciprocal resistance pathways such as those involved in xenobiotic metabolism. An ideal candidate is Scaptomyza flava, a drosophilid fly whose leafmining larvae are true herbivores that can be found in nature feeding on Arabidopsis and other crucifers. Here, we describe the life cycle of S.flava on Arabidopsis and use multiple approaches to characterize the response of Arabidopsis to S.flava attack. Oviposition choice tests and growth performance assays on different Arabidopsis ecotypes, defence-related mutants, and hormone and chitin-treated plants revealed significant differences in host preference and variation in larval performance across Arabidopsis accessions. The jasmonate and glucosinolate pathways in Arabidopsis are important in mediating quantitative resistance against S.flava, and priming with jasmonate or chitin resulted in increased resistance. Expression of xenobiotic detoxification genes was reduced in S.flava larvae reared on Arabidopsis jasmonate signalling mutants and increased in plants pretreated with chitin. These results and future research directions are discussed in the context of developing a genetic model system to analyse insect-plant interactions.

Differential preference of Capsicum spp. cultivars by Aphis gossypii is conferred by variation in volatile semiochemistry

The aim of this study was to demonstrate that Capsicum spp. cultivars are differentially preferred by the cotton aphid, Aphis gossypii, and to investigate the role of volatile semiochemicals in conferring differences in host preferences. Two preference assays were conducted in 2008 under greenhouse conditions. Fourteen different commercially available cultivars were grown in cages protected by an anti-aphid net, and were infested 60 days after planting, through the release of ten adult female A. gossypii per plant. The results showed that after a five-day infestation period, statistically significant differences in the mean number of A. gossypii between cultivars were observed, with Sweet Pepper Hybrid Green Belt (SPHGB) being one of the cultivars with the lowest number of A. gossypii per plant. To test the hypothesis that the preference of cultivars was associated with release of volatile, Capsicum spp-derived semiochemicals, olfactometer behavior bioassays were conducted with A. gossypii, using volatile organic compounds (VOCs) collected from non-preferred SPHGB and preferred SPAB cultivars. A. gossypii was significantly repelled only by the VOCs of infested SPHGB. Furthermore, coupled gas chromatography-mass spectrometry (GC-MS) analysis of VOCs released by plants prior to, and after, A. gossypii infestation, revealed that the non-preferred SPHGB cultivar released nine additional compounds after infestation, including 6-methyl-5-hepten-2-one, a known plant defense semiochemical involved in plant—aphid interactions. These data suggest that non-preferred cultivars releasing this semiochemical have the potential to be used in breeding programs aimed at producing A. gossypii-resistant Capsicum spp. cultivars.

Consequences of the expanding global distribution of Aedes albopictus for dengue virus transmission.

The dramatic global expansion of Aedes albopictus in the last three decades has increased public health concern because it is a potential vector of numerous arthropod-borne viruses (arboviruses), including the most prevalent arboviral pathogen of humans, dengue virus (DENV). Ae. aegypti is considered the primary DENV vector and has repeatedly been incriminated as a driving force in dengue's worldwide emergence. What remains unresolved is the extent to which Ae. albopictus contributes to DENV transmission and whether an improved understanding of its vector status would enhance dengue surveillance and prevention. To assess the relative public health importance of Ae. albopictus for dengue, we carried out two complementary analyses. We reviewed its role in past dengue epidemics and compared its DENV vector competence with that of Ae. aegypti. Observations from “natural experiments” indicate that, despite seemingly favorable conditions, places where Ae. albopictus predominates over Ae. aegypti have never experienced a typical explosive dengue epidemic with severe cases of the disease. Results from a meta-analysis of experimental laboratory studies reveal that although Ae. albopictus is overall more susceptible to DENV midgut infection, rates of virus dissemination from the midgut to other tissues are significantly lower in Ae. albopictus than in Ae. aegypti. For both indices of vector competence, a few generations of mosquito colonization appear to result in a relative increase of Ae. albopictus susceptibility, which may have been a confounding factor in the literature. Our results lead to the conclusion that Ae. albopictus plays a relatively minor role compared to Ae. aegypti in DENV transmission, at least in part due to differences in host preferences and reduced vector competence. Recent examples of rapid arboviral adaptation to alternative mosquito vectors, however, call for cautious extrapolation of our conclusion. Vector status is a dynamic process that in the future could change in epidemiologically important ways.

Differences in Host Preference, Life Cycle Pattern, and Insecticide Susceptibility Among <I>Aphis gossypii</I> Clones and Genetic Relationships Inferred from Internal Transcribed Spacer 2 Sequences of rDNA

As part of an analysis of the genetic structure of Aphis gossypii Glover, one of the most polyphagous aphids and a pest of global agricultural importance, the ITS2 rDNA region was sequenced and compared among 38 Japanese aphid clones with different life cycles, host preferences, and insecticide susceptibilities. The preference of each clone for cucumber (Cucumis sativus L.), eggplant (Solanum melongena L.), citrus (Citrus unshiu Marcovitch), and pear (Pyrus pyrifolia Nakai) as a host was tested. About two thirds of the clones preferred cucumber or eggplant. No other particular combination of host plants was preferred. Five types of life cycle were found: holocyclic I, holocyclic II, intermediate, androcyclic, and anholocyclic. Each clone showed a different level of susceptibility to each of three insecticides. Apparent correlation between the various attributes was not found. Phylogenetic trees constructed from internal transcribed spacer 2 sequences showed ambiguous relationships between genetic differentiation and host preference.

Genetic, ecological, behavioral and geographic differentiation of populations in a thistle weevil: implications for speciation and biocontrol

Because weevils are used as biocontrol agents against thistles, it is important to document and understand host shifts and the evolution of host-specificity in these insects. Furthermore, such host shifts are of fundamental interest to mechanisms of speciation. The mediterranean weevil Larinus cynarae normally parasitizes either one of two thistle genera, Onopordum and Cynara, being locally monophagous. In Sardinia, however, both host genera are used. We used three types of data to help understand this complex host use: (i) weevil attack rates on the two host genera among 53 different populations in Sardinia and nearby Corsica, (ii) host preference in a lab setting, and (iii) genetic (allozyme) differentiation among weevil populations exploiting the same or different hosts. Using a subset of populations from northern Sardinia, we attempted to relate interpopulation differences in host preference to gene flow among populations by comparing pairwise differences in oviposition preference (Qst) and in allozyme frequencies (Fst). Overall, Qst and Fst were positively correlated. Fst was positively correlated with geographic distance among pairs of populations using the same host, but not among different-host population pairs. As mating occurs on the hosts, this result suggests reinforcement. Genetic evidence indicates Cynara as the ancestral host of the weevils from both islands and our current studies suggest repeated attempts to colonize Onopordum, with a successful shift in Corsica and a partial shift in Sardinia. This scenario would explain why in Sardinia the level of attack was higher on Cynara than on Onopordum and why, when given a choice in the laboratory, Sardinian weevils preferred Cynara even when sampled from Onopordum. The lability of host shifts in L. cynarae supports caution in using these or related weevils as biocontrol agents of exotic thistles.

GENETICS, EXPERIENCE, AND HOST-PLANT PREFERENCE IN EUROSTA SOLIDAGINIS: IMPLICATIONS FOR HOST SHIFTS AND SPECIATION

Abstract Host‐associated mating is crucial in maintaining the partial reproductive isolation between the host races of Eurosta solidaginis (Diptera: Tephritidae), a fly that forms galls on Solidago altissima and S. gigantea. (We refer to flies reared from S. gigantea as gigantea flies and those reared from S. altissima as altissima flies.) We measured the host preference of males and females of both host races, F1 hybrids between the host races, F2, and backcrosses to both host races. Male and female altissima flies and female gigantea flies had high host fidelity, whereas male gigantea flies had low host fidelity. This result suggests that there may be gene flow between the host races due to nonassortative mating that occurs when male gigantea mate with altissima females on S. altissima. This indicates assortative‐mating mechanisms in addition to host‐associated mating are required to produce the partial reproductive isolation between the host races that has been observed. Nongenetic factors had no influence on host preference. Larval conditioning did not influence host preference: reciprocal F1 hybrids reared in S. altissima and S. gigantea both preferred S. gigantea. Adult experience had no impact on host preference: females preferred their natal host plant regardless of which host they encountered first as an adult. The hypothesis that maternal effects influence preferences was rejected because male and female flies did not show a consistent preference for the host plant of their mother. We also found no evidence that preference was a sex‐linked trait because F1 and backcrosses to the host races with different combinations of X chromosomes from the two host races preferred S. gigantea. Our results indicate that host preference is not determined by a large number of genes because preference of hybrids did not correspond to the proportion of the genome derived from each host race. The strength of the ovipuncture preference for S. gigantea by gigantea females, the females of both reciprocal F1 hybrids, the backcross to gigantea, and F2s indicates that preference is inherited nonadditively at a limited number of loci. The F1 female hybrids, however, had a weaker host preference for S. gigantea than the pure gigantea host race, indicating that there may be incomplete dominance or modifier loci. Males had different host preference patterns than females, with individual male gigantea and male F1 hybrids usually exhibiting preference exclusively for S. gigantea or S. altissima. One hypothesis explaining the difference in host preference between males and females is that the same gene influences both female and male host preference, but it is a sex‐influenced gene. Thus, males carrying the gene for S. gigantea preference have an intermediate host preference, whereas females have a strong host preference to S. gigantea. In summary, we found that the host preference that produces host‐associated mating is inherited nonadditively at a relatively small number of loci on autosomal genes. This mode of inheritance meets the assumptions of models of sympatric speciation, indicating that the host races could have evolved in sympatry.

Morphological description and illustration of female developmental stages of Stictococcus vayssierei (Homoptera: Stictococcidae)

The African root and tuber scale Stictococcus vayssierei Richard is the only known hypogeal species of the family Stictococcidae. Its wide range of host plants together with concurrently field observed differences in host preference provided evidence of polyphagy or the involvement of more than a single-scale species. To establish the baseline information for future taxonomic studies, newly emerged larvae were collected from infested cassava from three sites in the humid forest zone of southern Cameroon. A glass binocular magnifier was used to observe morphological changes of live individuals and slide-mounted individuals of all developmental stages were examined with a compound microscope. Stictococcus vayssierei females went through three developmental stages—two larval instars and an adult stage. The first and second instars were purple-red, while the adult was brown. Body size and the degree of sclerotization of the dorsal line increased in each developmental stage. White waxy secretions on the basal periphery of the second instar, and both dorsum and periphery of the adults, distinguished them from the first instar, which lacks the white waxy secretions. On slide-mounted specimens, certain aspects of the anal complex (i.e. number of opercular plates and -setae) were found to be the most discriminating features of S. vayssierei life stages. These results are useful for further studies on the diversity of subterranean stictoccocid scales.

Preferential nodulation of Glycine max, Glycine soja and Macroptilium atropurpureum by two Bradyrhizobium species japonicum and elkanii

Soybean bradyrhizobia, Bradyrhizobium japonicum and Bradyrhizobium elkanii differ in various traits such as DNA fingerprint, rhizobitoxine production, indole-3-acetic acid production and uptake of hydrogenase. In this communication, we investigated whether the differences between both species extend to host preference in multistrain environments. Nodule occupancy of B.japonicum and B. elkanii significantly depended on host plants. B. japonicum and B. elkanii preferentially nodulated Glycine max and M. atropurpureum, respectively. Both bacterial species were shown to nodulate G. soja with similar efficiency. There was a significant divergence of DNA sequences in and around nodulation genes between the B. japonicum and B. elkanii field isolates. However, flavonoid and lipo-chitin nodulation signals were not involved in the difference in host preference of B. japonicum and B. elkanii. The ecological implications of host preference are discussed.

The chemosensory basis for behavioral divergence involved in sympatric host shifts. I. Characterizing olfactory receptor neuron classes responding to key host volatiles

The recent shift of Rhagoletis pomonella from its native host hawthorn to introduced, domestic apple has been implicated as an example of sympatric speciation. Recent studies suggest that host volatile preference might play a fundamental role in host shifts and subsequent speciation in this group. Single sensillum electrophysiology was used to test a proposed hypothesis that differences in R. pomonella olfactory preference are due to changes in the number or odor specificity of olfactory receptor neurons. Individuals were analyzed from apple, hawthorn, and flowering dogwood-origin populations, as well as from the blueberry maggot, Rhagoletis mendax Curran (an outgroup). Eleven compounds were selected as biologically relevant stimuli from previous electroantennographic/behavioral studies of the three R. pomonella populations to host fruit volatiles. Cluster analysis of 99 neuron responses showed that cells from all tested populations could be grouped into the same five classes, ranging from those responding to one or two volatiles to those responding to several host volatiles. Topographical mapping also indicated that antennal neuron locations did not differ by class or fly taxa. Our results do not support the hypothesis that differences in host preference among Rhagoletis populations are a result of alterations in the number or class of receptor neurons responding to host volatiles.

Distribution of dominant arbuscular mycorrhizal fungi among five plant species in undisturbed vegetation of a coastal grassland

Most plant species in mixed grassland vegetation are colonized by arbuscular mycorrhizal (AM) fungi. Previous studies have reported differences in host preferences among AM fungi, although the fungi are known to lack host specificity. In the present study, the distribution of phylogenetic groups of AM fungi belonging to a clade of Glomus species was studied in five plant species from a coastal grassland in Denmark. The occurrence of the fungi was determined by PCR analyses of fungal large subunit ribosomal DNA sequences amplified from root fragments using a specific primer set. The results showed that the dominant Glomus species were able to colonize all the studied plant species, supporting the view that the AM fungi represent a large underground interconnecting mycelial network.

A new potential host and transmission routes of Thripinema nicklewoodi, an entomogenous nematode of western flower thrips

Abstract Thripinema nicklewoodi Siddiqi is an obligate parasite of Frankliniella occidentalis Pergande. Potential parasitism by T. nicklewoodi of three other thrips species was examined under laboratory conditions. The test thrips included one predaceous thrips ( Franklinothrips orizabensis Johansen) and two phytophagous thrips in the family Thripidae, one of which is in the subfamily Thripinae ( Thrips tabaci Lindeman) and the other in the subfamily Panchaetothripinae ( Heliothrips haemorrhoidalis Bouche). After presenting the nematode with second instar larval thrips, we found that the nematode penetrated the test thrips in no choice tests. However, H. haemorrhoidalis and F. orizabensis were intrinsically unsuitable as hosts since the nematode did not produce any eggs 10 days after nematode penetration. Only T. tabaci , in the subfamily Thripinae, was suitable for reproduction by the nematode. The reproduction capability was equal to its usual host F. occidentalis . No significant differences in host preference were found between F. occidentalis and each of the three test species in choice tests. These results indicate that T. tabaci is a new potential host of T. nicklewoodi . In addition, in scanning electron microscopy studies, transmission routes of T. nicklewoodi were photographed in F. occidentalis . These photographs show that nematodes penetrated larval F. occidentalis through the intersegmental membranes of a coxal cavity or the abdomen and exited adult thrips via the anus.

Difference in Host Preference between Two Populations of the Freshwater Pearl Mussel Margaritifera laevis (Bivalvia: Margantiferidae) in the Shinano River System, Japan

Difference in Host Preference between Two Populations of the Freshwater Pearl Mussel Margaritifera laevis (Bivalvia: Margantiferidae) in the Shinano River System, Japan

Species and host record of the Bactrocera dorsalis complex (Diptera: Tephritidae) detected by the plant quarantine of Japan

Seven species of the Bactrocera dorsalis complex, B. dorsalis, B. papayae, B. carambolae, B. philippinensis, B. occipitalis, B. caryeae and B. kandiensis, were found in a total of 1,093 specimens collected from 136 fruit samples carried by travelers from Asian countries and intercepted by the plant quarantine at Narita Airport of Japan from 1979 to 1998. Two sympatric species combinations, i.e., B. philippinensis vs. B. occipitalis and B. papayae vs. B. carambolae, were distinguished based on aculeus and aedeagal length. However, no difference in aculeus and aedeagal length was found between the other two sympatric species combinations, i.e., B. dorsalis vs. B. kandiensis and B. dorsalis vs. B. caryeae. A comparison of the detection frequency in each host fruit between the two sympatric species of the above two combinations suggests that B. papayae and B. carambolae have different host preferences while B. philippinensis and B. occipitalis have no differences in host preference.

Genetic variation in Microctonus aethiopoides (Hymenoptera: Braconidae)

Abstract The Palaearctic parasitoid Microctonus aethiopoides Loan (Hymenoptera: Braconidae) has been introduced to North America for biological control of weevils in the genera Sitona and Hypera (Coleoptera: Curculionidae) and to Australia and New Zealand for control of Sitona discoideus Gyllenhal. Various geographic and host-associated populations of M. aethiopoides have exhibited differences in host preference, host range, and adult morphology. These differences have generally been interpreted as indicative of genetically differentiated biotypes of M. aethiopoides, but direct genetic evidence of biotypic variation has been lacking. Nucleotide sequence data were generated from the gene regions COI, 16S, 28S, and β-tubulin to assess genetic variation among M. aethiopoides reared from various host species collected in Australia, Iran, New Zealand, the United States, and 10 European countries. Ten adult morphological characters were also measured to validate the identity of the specimens and to assess morphological variation among the geographic and host-associated populations. Parsimony and maximum likelihood analyses of the COI, 16S, and β-tubulin sequences provided strong support for the presence of at least two M. aethiopoides biotypes, one associated with Hypera species and the other with Sitona species. There was also evidence for genetic divergence among parasitoids associated with different Sitona species. Morphological variation was also closely correlated with host species, but the occurrence of morphological variation in the absence of genetic variation suggested morphological characters should be used cautiously with M. aethiopoides biotypes.

Genetics, experience, and host-plant preference in Eurosta solidaginis: implications for host shifts and speciation.

Host-associated mating is crucial in maintaining the partial reproductive isolation between the host races of Eurosta solidaginis (Diptera: Tephritidae), a fly that forms galls on Solidago altissima and S. gigantea. (We refer to flies reared from S. gigantea as gigantea flies and those reared from S. altissima as altissima flies.) We measured the host preference of males and females of both host races, F1 hybrids between the host races, F2, and backcrosses to both host races. Male and female altissima flies and female gigantea flies had high host fidelity, whereas male gigantea flies had low host fidelity. This result suggests that there may be gene flow between the host races due to nonassortative mating that occurs when male gigantea mate with altissima females on S. altissima. This indicates assortative-mating mechanisms in addition to host-associated mating are required to produce the partial reproductive isolation between the host races that has been observed. Nongenetic factors had no influence on host preference. Larval conditioning did not influence host preference: reciprocal F1 hybrids reared in S. altissima and S. gigantea both preferred S. gigantea. Adult experience had no impact on host preference: females preferred their natal host plant regardless of which host they encountered first as an adult. The hypothesis that maternal effects influence preferences was rejected because male and female flies did not show a consistent preference for the host plant of their mother. We also found no evidence that preference was a sex-linked trait because F1 and backcrosses to the host races with different combinations of X chromosomes from the two host races preferred S. gigantea. Our results indicate that host preference is not determined by a large number of genes because preference of hybrids did not correspond to the proportion of the genome derived from each host race. The strength of the ovipuncture preference for S. gigantea by gigantea females, the females of both reciprocal F1 hybrids, the backcross to gigantea, and F2s indicates that preference is inherited nonadditively at a limited number of loci. The F1 female hybrids, however, had a weaker host preference for S. gigantea than the pure gigantea host race, indicating that there may be incomplete dominance or modifier loci. Males had different host preference patterns than females, with individual male gigantea and male F1 hybrids usually exhibiting preference exclusively for S. gigantea or S. altissima. One hypothesis explaining the difference in host preference between males and females is that the same gene influences both female and male host preference, but it is a sex-influenced gene. Thus, males carrying the gene for S. gigantea preference have an intermediate host preference, whereas females have a strong host preference to S. gigantea. In summary, we found that the host preference that produces host-associated mating is inherited nonadditively at a relatively small number of loci on autosomal genes. This mode of inheritance meets the assumptions of models of sympatric speciation, indicating that the host races could have evolved in sympatry.

Evidence for differential host preference in Microdochium nivale var. majus and Microdochiumnivale var. nivale

The pathogenicity of Microdochium nivale var. majus and var. nivale was tested on wheat, rye and oat seedlings using both visual disease scoring and quantitative PCR measurements. In an individual inoculation trial at 10°C var. majus and var. nivale were strongly pathogenic towards wheat and rye, with var. nivale causing slightly greater disease in rye. At this temperature only var. nivale caused significant disease of oats. In a further experiment M. nivale was inoculated as a series of mixtures of the two varieties and incubated at 15°C. The ratio of the varieties present in the inoculum and present at harvest was analysed by quantitative PCR and this enabled a coefficient of selection to be calculated for the varieties on each host. M. nivale var. majus showed a weak selective advantage over var. nivale on wheat (0.33 ± 0.08) and oat seedlings (0.35 ± 0.016) and M. nivale var. nivale showed a strong selective advantage over var. majus on rye seedlings (0.92 ± 0.26). The isolates were also compared for sensitivity to benzoxazolinone (BOA), a hydroxamic acid compound derived from rye leaves. M. nivale var majus was found to be significantly more sensitive to BOA than M. nivale var. nivale, indicating a possible mechanism for the selective advantage of var. nivale growing on rye. This is the first substantiated indication of a significant difference in host preference between Microdochium nivale var. majus and var. nivale.

Olfactory sensitivities of mosquitoes with different host preferences ( Anopheles gambiae s.s., An. arabiensis, An. quadriannulatus, An. m. atroparvus) to synthetic host odours

Responses of antennal olfactory cells associated with sensilla trichodea were recorded in females of four Anopheles species (Diptera, Culicidae) with different host preferences: the anthropophilic An. gambiae s.s., the opportunistic An. arabiensis, and the zoophilic An. quadriannulatus and An. maculipennis atroparvus. Stimuli were vapours of synthetic host-odours: ethanoic, propanoic, butanoic, 3-methyl propanoic, 4-methyl butanoic acid, 1-octen-3-ol, and 3- and 4-methyl phenol. On stimulation with fatty acids and phenols either excitation or inhibition of spike activity was found, whereas responses to 1-octen-3-ol were invariably excitatory. The odour spectra of the cells could include activating as well as inhibiting substances. Differences in host preferences may be reflected in the numbers of olfactory cells responding to different odours and/or in the sensitivities of these cells. In An. gambiae more cells were excited by fatty acids than in An. arabiensis and An. m. atroparvus, whereas inhibition occurred more often in the latter two species. In addition, the fatty acid-excited cells in An. gambiae were more sensitive to these substances than in An. m. atroparvus and An. quadriannulatus. On the contrary, in the latter two species cells were more responsive to 1-octen-3-ol. In An. arabiensis, responses of stimulus-excited cells were intermediate between those in the anthropophilic and zoophilic species.

Evidence for the occurrence of sibling species inEubazusspp. (Hymenoptera: Braconidae), parasitoids ofPissodesspp. weevils (Coleoptera: Curculionidae)

AbstractComparative studies were made on three presumed sibling species of the genusEubazus, parasitoids of EuropeanPissodesspp. weevils, to clarify their taxonomy and define diagnostic characters. Several populations ofE. semirugosus(Nees),E. robustus(Ratzeburg) andEubazussp. were compared with respect to their morphology (mainly through morphometric analyses), fecundity, isoenzyme patterns and host preference. Crosses were made to assess the genetic and behavioural compatibility of the populations. In addition, the North AmericanE. crassigaster(Provancher), a parasitoid ofPissodes strobi(Peck), was compared toE. semirugosus, a species selected for introduction againstP. strobiin Canada. The ratio of the length of the ovipositor sheath to the fore wing length was the most discriminating morphometric variable, but discriminant analyses including several measurements were needed to completely separate European species. A canonical discriminant function provided a total separation between males ofE. crassigasterandE. semirugosus, but not between females.Eubazus crassigasterandE. semirugosuswere totally separated by the banding pattern of the enzyme phosphogluconate dehydrogenase whereas hexokinase and esterase provided a diagnostic separation betweenEubazussp. andE. robustus. Eubazussp. differed from all the other species by having a greater number of ovarioles and, consequently, a higher potential fecundity. In a two-choice oviposition test,E. semirugosusandEubazussp. showed a significant preference for their natural host,P. castaneusDe Geer andP. piceae(Illiger), respectively. A similar test made with their progenies reared under standard conditions showed that the difference in host preference was genetically fixed. Males and females of different species did not mate readily, in contrast to individuals from the same species. All attempts to interbreedE. robustusandEubazussp. failed, but a few crosses betweenE. semirugosusand the two other European species produced fertile offspring. These observations strongly suggest that the complex ofEubazusspp. parasitoids attackingPissodesspp. in Europe is composed of at least three sibling species, two of which appear to have specialized on distinct host species that occupy exclusive microhabitats.

Differential responses of mosquito sibling species Anopheles arabiensis and An. quadriannulatus to carbon dioxide, a man or a calf.

Field studies on responses of two mosquito sibling species, Anopheles arabiensis Patton and An. quadriannulatus Theobald, to a man, a calf and different release rates of carbon dioxide (man, calf and cow equivalents) were conducted in north-eastern South Africa. Various combinations of baits were compared in two-choice tests, using two mosquito nets, placed 2.5 m apart and 10 cm off the ground. Mosquitoes attracted to the baits were able to enter the nets from below and were collected by means of a suction tube. In a two-choice test between a man and CO2 (human equivalent, 250 ml/min), 81% of the An. quadriannulatus were caught with CO2. The reverse was seen for An. arabiensis, where only 20% of the total catch was caught with CO2 compared to man. High release rates of CO2 (cow equivalent, 800 ml/min) attracted significantly more An. quadriannulatus than the low release rate (250 ml/min), whereas no significant effect of the release rate of CO2 on the total catch of An. arabiensis was seen. In the latter species, up to 33% of the attraction of human emanation is attributable to carbon dioxide. Anopheles quadriannulatus was equally attracted to a calf and CO2 (calf equivalent, 180 ml/min). Catches of other mosquito species showed consistent differences between all treatments which appear to be associated with differences in host-preference, suggesting that the importance of CO2 in host-seeking behaviour of mosquitoes increases with the degree of zoophily.