Behavioural responses of Phlebotomus duboscqi to plant-derived volatile organic compounds.

Phlebotomine sand flies are vectors of Leishmania parasites that cause leishmaniases. Both sexes of sand flies feed on plants primarily for sugars, although the chemical cues that mediate attraction to host plants remain largely unknown. Previously, using coupled gas chromatography-mass spectrometry, the authors identified several volatile organic compounds (VOCs) common to preferred host plants for selected Afrotropical sand flies from the Fabaceae family. Of the identified volatiles, the significance of the monoterpenes linalool oxide, ocimene and p-cymene and the benzenoid m-cresol, p-cresol in sand fly behaviour is unknown. In olfactometer assays, the authors tested these compounds singly and in blends for their attractiveness to Phlebotomus duboscqi, cutaneous leishmaniasis vector in Kenya. In dose-response assays, single compounds increased the responses of males and females over controls, but their optimum attractive doses varied between the sexes. Two five-component blends, referred to as Blend-f and Blend-m for females and males respectively, were formulated and tested in dose-response assays against 1-octen-3-ol (positive control). The results of the present study showed that males and females were significantly attracted to varying levels of the two blends. In pairwise assays, the authors evaluated the most attractive of these blends to each sex (i.e., Blend Am for male against Blend Bf for female), revealing that males were attracted to both blends at varying levels, whereas females were indifferent. The study's results demonstrate that plant-derived VOCs can be exploited for sand fly management.

Swarming and mating activity of Anopheles gambiae mosquitoes in semi-field enclosures.

Anopheles gambiae Giles sensu stricto (Diptera: Culicidae) is the major Afro-tropical vector of malaria. Novel strategies proposed for the elimination and eradication of this mosquito vector are based on the use of genetic approaches, such as the sterile insect technique (SIT). These approaches rely on the ability of released males to mate with wild females, and depend on the application of effective protocols to assess the swarming and mating behaviours of laboratory-reared insects prior to their release. The present study evaluated whether large semi-field enclosures can be utilized to study the ability of males from a laboratory colony to respond to natural environmental stimuli and initiate normal mating behaviour. Laboratory-reared males exhibited spatiotemporally consistent swarming behaviour within the study enclosures. Swarm initiation, peak and termination time closely tracked sunset. Comparable insemination rates were observed in females captured in copula in the semi-field cages relative to females in small laboratory cages. Oviposition rates after blood feeding were also similar to those observed in laboratory settings. The data suggest that outdoor enclosures are suitable for studying swarming and mating in laboratory-bred males in field-like settings, providing an important reference for future studies aimed at assessing the comparative mating ability of strains for SIT and other vector control strategies.

Molecular markers reveal narrow genetic base and culturing-associated genetic drift in Teretrius nigrescens Lewis populations released for the biological control of the larger grain borer in Africa.

In biological control, successful establishment of a natural enemy species depends on its adaptability in the introduced range including its ability to re-establish desired ecological interactions with the pest. These are affected by genetic parameters hitherto largely unresolved in biological control. The larger grain borer (LGB), Prostephanus truncatus, an invasive species from meso-America, is the most important post-harvest pest of maize in Africa. We studied the genetic structure of Teretrius nigrescens, a predatory beetle previously released for the control of the pest in Africa, to test the hypothesis that establishment patterns were a result of ecotype-environment mismatch and to follow up on our earlier reports of distinct lineages of the predator. We studied 13 populations of T. nigrescens, using 16 polymorphic microsatellite markers. Five genetic populations with a hierarchical structure and significant isolation by distance were detected. The most diverse population was found in southern Mexico, consistent with earlier lineage coexistence observations. Populations introduced to Africa maintained genetic similarity to local geographic populations of their area of origin. The more successful Benin releases were also more genetically diverse. Loss of rare alleles and a higher frequency of existing private alleles in some populations indicated population expansions following bottleneck events. Sustainable biological control should accommodate pest and natural enemy species, and monitor genetic changes associated with introduction and release.

Selection of promising fungal biological control agent of the western flower thrips Frankliniella occidentalis (Pergande).

AIMS: Larval stages of Frankliniella occidentalis are known to be refractory to fungal infection compared with the adult stage. The objective of this study was to identify promising fungal isolate(s) for the control of larval stages of F. occidentalis. METHODS AND RESULTS: Ten isolates of Metarhizium anisopliae and eight of Beauveria bassiana were screened for virulence against second-instar larvae of F. occidentalis. Conidial production and genetic polymorphism were also investigated. Metarhizium anisopliae isolates ICIPE 7, ICIPE 20, ICIPE 69 and ICIPE 665 had the shortest LT(50) values of 8.0-8.9 days. ICIPE 69, ICIPE 7 and ICIPE 20 had the lowest LC(50) values of 1.1 × 10(7), 2.0 × 10(7) and 3.0 × 10(7) conidia ml(-1), respectively. Metarhizium anisopliae isolate ICIPE 69 produced significantly more conidia than M. anisopliae isolates ICIPE 7 and ICIPE 20. Internally transcribed spacers sequences alignment showed differences in nucleotides composition, which can partly explain differences in virulence. CONCLUSION: These results coupled with the previous ones on virulence and field efficacy against other species of thrips make M. anisopliae isolate ICIPE 69 a good candidate. SIGNIFICANCE AND IMPACT OF THE STUDY: Metarhizium anisopliae isolate ICIPE 69 can be suggested for development as fungus-based biopesticide for thrips management.

Phylogeographic structure of Teretrius nigrescens (Coleoptera: Histeridae) predator of the invasive post harvest pest Prostephanus truncatus (Coleoptera: Bostrichidae).

The invasive larger grain borer Prostephanus truncatus (Horn) is the most important pest of farm-stored maize in Africa. It was introduced into the continent from Mesoamerica in the late 1970s and by 2008 had spread to at least 18 countries. Classical biological control using two populations of the predator Teretrius nigrescens Lewis achieved long-term and cost effective control in warm-humid areas, but not in cool and hot-dry zones. The present study investigated the phylogenetic relationships between geographical populations of the predator. Ten populations of T. nigrescens were studied using randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR), sequence analysis of mitochondrial Cytochrme oxydase 1 (mtCOI) gene and ribosomal internally transcribed spacers (ITS) 1, 5.8S and ITS2. The mtCOI variation revealed two clades associated with geographical regions in Central America. It also reveals a significant isolation by distance between populations and considerable genetic shifts in laboratory rearing. RAPD-PCR did not reveal any potential SCAR diagnostic markers. The ITS variation mainly involved insertions and deletions of simple sequence repeats even within individuals. This study reveals the existence of two different mitochondrial lineages of the predator, associated with the geographical origin of populations distinguishable by fixed mutations on the mtCOI gene. The populations of T. nigrescens released in Africa belonged to two different clades from Meso America, namely south (released in West Africa) and north (released in eastern Africa). However, more polymorphic markers are required to clarify the observations in demographic time scales.

Detection of phytoplasma by loop-mediated isothermal amplification of DNA (LAMP).

Napier stunt phytoplasma (16SrXI and 16SrIII) in eastern Africa is a serious threat to the expansion of Napier grass (Pennisetum purpureum) farming in the region, where it is widely cultivated as fodder in zero grazing livestock systems. The grass has high potential for bio-fuel production, and has been adopted by farmers as a countermeasure to cereal stem borer Lepidoptera, since it attracts and traps the insect. Diagnosis of stunt phytoplasma have been largely by nested polymerase chain reaction (nPCR) targeting the 16S rRNA gene. However, the method is laborious, costly and technically demanding. This investigation has developed a simpler but effective phytoplasma diagnostic tool, called; loop-mediated isothermal amplification of DNA (LAMP). The assay was tested on 8 symptomatic and 8 asymptomatic plants, while its detection limit was compared to nested PCR using samples serially diluted from 3 ng/µl to 0.38 pg/µl. Molecular typing of LAMP products was determined by BsrI restriction digestion and Southern blot analysis. The assay sensitivity, positive and negative predictive values were estimated, while the specificity was tested on 11 phytoplasma groups. LAMP was specific to 5 phytoplasma groups: 16SrVI, X, XI and XVI. BsrI restriction digestion produced two predicted fragments, and there was specific binding of probe DNA to the LAMP amplicons in Southern blot analysis. The assay sensitivity was 100%, while the positive and negative predictive values were 63 and 100% respectively. LAMP was 20-fold more sensitive than nested PCR. This study validates LAMP for routine diagnosis of Napier stunt and other closely related phytoplasmas.

Uncovering the tracks of a recent and rapid invasion: the case of the fruit fly pest Bactrocera invadens (Diptera: Tephritidae) in Africa.

Phytophagous insects of the genus Bactrocera are among the most economically important invasive fruit fly pests. In 2003, an unknown Bactrocera species was found in Kenya. First identified as an 'aberrant form' of the Asian B. dorsalis complex, it was later recognized as a new species, Bactrocera invadens. Within 2 years of its discovery, the species was recorded in several African countries, becoming an important quarantine pest. As this invasive fly was discovered only recently, no data are available on its invasion pattern in Africa. This pilot study attempts to infer from genetic data the dynamic aspects of the African invasion of this pest. Using microsatellite markers, we evaluated the level of genetic diversity and the extent of common ancestry among several African populations collected across the invaded areas. A sample from the Asian Sri Lankan population was analysed to confirm the Asian origin of this pest. Genetic data cast no doubt that Sri Lanka belongs to the native range, but only a small percentage of its genotypes can be found in Africa. African populations display relatively high levels of genetic diversity associated with limited geographical structure and no genetic footprints of bottlenecks. These features are indicative of processes of rapid population growth and expansion with possible multiple introductions. In the span of relatively few years, the African invasion registered the presence of at least two uncorrelated outbreaks, both starting from the East. The results of the analyses support that invasion started in East Africa, where B. invadens was initially isolated.

Isolation and characterization of microsatellite markers from Teretrius nigrescens Lewis (Coleoptera: Histeridae), predator of the storage pest Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae).

Teretrius nigrescens is a predator of the larger grain borer (LGB) Prostephanus truncatus, an invasive post-harvest pest in Africa. We describe the isolation and characterization of 24 novel polymorphic microsatellite markers and their testing on a population from Honduras. Alleles per locus ranged between 2 and 12, and observed heterozygosity between 0.037 and 0.646. Six loci deviated significantly from Hardy-Weinberg equilibrium and showed evidence of null alleles. These markers will be useful for studies of the predator's population structure and characterizing populations for control of LGB.

Comparison of five allopatric fruit fly parasitoid populations (Psyttalia species) (Hymenoptera: Braconidae) from coffee fields using morphometric and molecular methods.

Morphometric studies of five allopatric parasitoid populations (genus Psyttalia Walker) from coffee plantations in Cameroon (Nkolbisson), Ghana (Tafo) and Kenya (Rurima, Ruiru and Shimba Hills) and one non-coffee population (from Muhaka, Kenya) were compared with individuals of Psyttalia concolor (Szépligeti), a species released in several biological control programmes in the Mediterranean Region since the 20th Century. Analyses of wing vein measurements showed the second submarginal cell of the fore wing and its adjoining veins had the heaviest principal component weights and served as the main contributing variables in the diagnostic differentiation of the populations. Two populations (Rurima and Ruiru) were found to be the closest to each other and with the strongest phenetic affinity toward P. concolor (and forming one cluster). Populations from Shimba Hills (of unknown identity), Nkolbisson (P. perproximus (Silvestri)) and Tafo formed a second cluster and were separated from P. concolor. Comparison using amplified fragment length polymorphism (AFLP) also showed the Shimba, Nkolbisson and Tafo populations forming a cluster in a dendrogram generated from their genetic distances, with the Shimba and Tafo populations placed as the most closely related species. Based on consistent morphological similarities, morphometric and ecological data coupled with the genetic evidence from AFLP data, the Shimba population is suggested as belonging to the P. perproximus group and, thus, represents a new occurrence record in Kenya. Our results also support earlier conclusion from cross mating data that populations from Rurima and Ruiru belong to the Psyttalia concolor species-group.

Isolation and characterization of microsatellite markers in the newly discovered invasive fruit fly pest in Africa, Bactrocera invadens (Diptera: Tephritidae).

We describe the isolation and characterization of 11 polymorphic microsatellite loci from the recently discovered fruit fly pest, Bactrocera invadens. The polymorphism of these loci was tested in individual flies from two natural populations (Sri Lanka and Democratic Republic of Congo). Allele number per locus ranged from three to 15 and eight loci displayed a polymorphic information content greater than 0.5. These microsatellite loci provide useful markers for studies of population dynamics and invasion history of this pest species.

Molecular diagnostics of economically important Ceratitis fruit fly species (Diptera: Tephritidae) in Africa using PCR and RFLP analyses.

The predominantly Afrotropical fruit fly genus Ceratitis contains many species of agricultural importance. Consequently, quarantine of Ceratitis species is a major concern for governmental regulatory agencies. Although diagnostic keys exist for identification of all described Ceratitis species, these tools are based on adult characters. Flies intercepted at ports of entry are usually immatures, and Ceratitis species cannot be diagnosed based on larval morphology. To facilitate identification of Ceratitis pests at ports of entry, this study explores the utility of DNA-based diagnostic tools for a select group of Ceratitis species and related tephritids, some of which infest agriculturally important crops in Africa. The application of the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method to analyse three mitochondrial genes (12S ribosomal RNA, 16S ribosomal RNA, and NADH-dehydrogenase subunit 6) is sufficient to diagnose 25 species and two species clusters. PCR analysis of the internal transcribed spacer region 1 (ITS-1) is able to distinguish three of the five species left unresolved by mitochondrial DNA analysis.

Characterization of Trypanosoma evansi type B.

A distinctive feature of Trypanosoma evansi is the possession of a kinetoplast that contains homogeneous DNA minicircles, but lacks DNA maxicircles. Two major sequence variants of the minicircle have been described and here we have sequenced the type B variant and designed a specific PCR test to distinguish it from type A. Further a test based on maxicircles to distinguish T. brucei brucei from T. evansi was designed and evaluated. Using the designed PCR tests, we detected three type B isolates from camel blood samples collected in northern Kenya, more than 20 years after the first isolation of type B. Comparison of minicircle sequences from all four type B isolates shows >96% identity within the group, and 50-60% identity to type A minicircles. Phylogenetic analysis based on minicircle sequences reveals two clusters, one comprising isolates of type A and one of type B, while random amplification of polymorphic DNA show slight polymorphic bands within type B. Most T. evansi isolates analysed were heterozygous at a repetitive coding locus (MORF2). All type B isolates had one genotype designated 3/5 based on the alleles present. Three camel isolates, which had homogenous type A minicircles, lacked the RoTat 1.2 gene, while another five isolates were T. b. brucei, based on the heterogeneity of their minicircles and presence of maxicircles as demonstrated by PCR amplification of the gene for cytochrome oxidase subunit 1. Our results confirm the existence of T. evansi type B isolates, T. b. brucei and existence of T. evansi type A without RoTat 1.2 gene in Kenyan isolates.

Growth and mortality in sheep and goats under high tsetse challenge in Kenya.

Trypanosomosis is a major impediment to livestock production and economic development in those areas of Africa where it is endemic. Although small ruminants appear to perform better than cattle in various agro-ecological zones, the importance of trypanosomosis has not been extensively investigated in these livestock. This study was designed to investigate the prevalence of trypanosomosis in sheep and goats in an endemic area and to evaluate the performance of different breeds under high tsetse challenge and the potential role of chemoprophylaxis in the control of the disease. The results showed that tsetse flies feed readily on small ruminants, and that these animals are susceptible to trypanosomosis. The Small East African goats acquired fewer infections than the Black Head Persian and Dorper sheep used in the study. In both sheep and goats, chemoprophylaxis with isometamidium chloride (Samorin, Rhone Merieux, Annecy, France) was protective, resulting in fewer infections and higher body weight gain. Trypanosomosis caused anaemia in both sheep and goats, and animals whose PCV fell below 15% rarely recovered, even with trypanocidal drug treatment. The peak transmission period was between 1 and 3 months after the peak tsetse fly density, which raises the possibility of effective strategic prophylaxis.

Financial implications of rearing sheep and goats under natural trypanosomosis challenge at Galana ranch, Kenya.

A study to compare the profitability of rearing sheep and goats under natural trypanosomosis challenge was carried out on Galana ranch in south-eastern Kenya between July 1996 and October 1997. Seventy-nine male weaner sheep and 79 male weaner goats were monitored monthly for weight changes and fortnightly for trypanosomosis. The animals of each species were divided into two groups. Group 1 was an untreated control, while group 2 was treated with isometamidium chloride (Samorin) at 0.5 mg/kg body weight every 3 months. In both groups, trypanosome infections were detected by microscopy and treated with diminazene aceturate (Veriben), at 3.5 mg/kg body weight, when the packed cell volume reached 17% or below. The profitability of each drug regime was expressed as the marginal revenue over the cost of trypanosomosis (MOT). There were greater losses occasioned by trypanosomosis in sheep than in goats. Animals of both species on chemoprophylaxis gave higher MOT values than those that received chemotherapy on diagnosis. However, the MOT values for the chemoprophylactic regime were higher for sheep than for goats, suggesting that the greater weight gain by sheep more then compensated for the higher cost of maintaining them under high trypanosomosis challenge. Thus, a Galana rancher would be better off keeping sheep rather than goats, other things being equal. The marginal revenue per dose of Samorin was lower than that of Veriben for both species, suggesting that strategic use of Samorin timed to precede the peak incidence of trypanosomosis might be a better option to raise the overall profitability in sheep and goats.

Amplified restriction fragment length polymorphism in parasite genetics.

The amplified restriction fragment length polymorphism (AFLP) technique is a relatively new method for the analysis of polymorphism that has not yet been widely used in parasitology. In this article, Dan Masiga, Andy Tait and Mike Turner provide a brief introduction to AFLP and illustrate how it can be used in the investigation of marker inheritance in genetic crosses and in the analysis of polymorphism of field populations. They also briefly highlight the strengths and weaknesses of AFLP in comparison with other methods for detecting polymorphism and conclude that AFLP is a very useful addition to the range of techniques available.

Comparative sensitivity of dot-ELISA, PCR and dissection method for the detection of trypanosome infections in tsetse flies (Diptera: glossinidae).

A visually read dot-enzyme linked immunosorbent assay (dot-ELISA) developed for the detection of trypanosomes in tsetse flies (Glossina spp.) was evaluated in the laboratory and under field conditions. In the evaluation, the fly dissection method was used as a standard technique and compared to the polymerase chain reaction (PCR). In laboratory studies, 133 and 126 tsetse flies were experimentally infected with different stocks of Trypanosoma brucei and T. congolense, respectively. Twenty-five days after infection, the flies were dissected and tested for the presence of trypanosomes using dot-ELISA and PCR. Dot-ELISA detected 98.4% of T. brucei and 94% of T. congolense infections in tsetse midguts, while PCR detected 97.6% of T. brucei and 96% of T. congolense tsetse midgut samples. For field evaluation of dot-ELISA, 700 tsetse flies were caught and screened for trypanosome infections by dissection. Seven of these (1%) had trypomastigotes in the midgut, 23 (3.3%) in the proboscis and none had trypanosomes in the salivary glands. All the flies with midgut infections also had trypanosomes in their proboscides. Five of the seven flies (71.4%) with midgut infections revealed by dissection, were also positive for T. congolense by the dot-ELISA and PCR techniques. Dot-ELISA detected T. congolense infections in an additional 86 (12.4%) of the 700 flies dissected. Of the 23 infections in the proboscis, 16 were T. vivax. Dot-ELISA detected 13 of the 16 (81%) while PCR detected 15 of 16 (94%) T. vivax infections. No T. brucei infection was detected by any of the methods in all the 700 tsetse flies examined. The results obtained from both the laboratory and field studies indicate that the dot-ELISA and PCR techniques are sensitive and species-specific in revealing trypanosome infections in tsetse flies. While dot-ELISA required a single test to detect T. congolense, several primer pairs were needed for PCR. The potential use of dot-ELISA as a tool for studying the epidemiology of trypanosomosis, while considering its field applicability and relatively lower cost is discussed.

A repetitive DNA sequence specific for Trypanosoma (Nannomonas) godfreyi.

The satellite DNA sequence of Trypanosoma (Nannomonas) godfreyi, a recently described parasite of Suidae, was determined. The sequence is 373bp in length, and contains two imperfect internal repeats of approximately 170bp. Like other trypanosome satellite DNAs, it has no extensive open reading frames and is probably non-coding. There is no significant homology with other major repetitive DNAs within subgenus Nannomonas. We have developed a PCR test that is specific for T. godfreyi and used it to identify the parasite in natural tsetse infections from Zimbabwe and Côte d'Ivoire. This test shows no cross reaction with non-target trypanosomes, even within subgenus Nannomonas, and will be invaluable in studies of the prevalence and distribution of T. godfreyi.

A high prevalence of mixed trypanosome infections in tsetse flies in Sinfra, Côte d'Ivoire, detected by DNA amplification.

The prevalence of various species and subgroups of trypanosomes in the Sinfra area of Côte d'Ivoire was determined using the polymerase chain reaction (PCR). Using this technique to amplify specific satellite DNA targets, it was possible to identify developmental-stage trypanosomes in the midguts and the proboscides of tsetse without expansion of parasite populations. The predominant tsetse species in the area was Glossina palpalis, while G. pallicera and G. nigrofusca were also present. Microscopical examination of 811 non-teneral flies revealed an infection rate of 14% in midguts and/or proboscides. Three subgroups of Trypanosoma congolense (Savannah, Forest & Kilifi), T. simiae, T. godfreyi, West African T. vivax and T. brucei ssp. were identified using PCR. T. congolense Forest was the most abundant of the Nannomonas trypanosomes. Approximately 40% of all infections were mixed, and there was a significantly higher prevalence of apparently mature T. brucei ssp. trypanosomes than has previously been reported. The present study demonstrates that PCR facilitates the easy identification of mature trypanosome infections in tsetse, providing a reliable estimation of trypanosomiasis challenge.

Multiple trypanosome infections in wild tsetse in Côte d'Ivoire detected by PCR analysis and DNA probes.

Trypanosomes were isolated from the midguts of Glossina palpalis palpalis, G. pallicera pallicera and G. nigrofusca nigrofusca captured around the village of Guediboua, South West of Daloa in Côte d'Ivoire. Seventy of the 124 isolates, obtained from 688 flies, were examined for four different kinds of trypanosome using the Polymerase Chain Reaction (PCR). Prevalences were: Trypanozoon 46%, riverine-forest T. congolense 86% and savannah T. congolense 54%. Only 29 samples were examined for T. simiae but it was not detected. Just 30% of the infections involved a single kind of trypanosome; the remainder were mixtures either of two (37%) or all three (27%) of the target organisms. 30 of the 70 isolates examined by PCR were successfully amplified to provide material for DNA probe hybridization. To a large extent, DNA probes confirmed the PCR results; all (28/28) of the riverine-forest and 82% (18/22) of the savannah T. congolense infections were identified. However, only 8% (1/13) of the PCR positives for Trypanozoon hybridized with the appropriate DNA probe. No T. simiae or T. godfreyi infections were identified using DNA probes but a large proportion (97%) (29/30) of the probed midguts were shown to contain Kilifi T. congolense. Four isolates out of 70 could not be identified by any method. There was no obvious association between the different species of flies and the infecting trypanosomes.

Sensitive detection of trypanosomes in tsetse flies by DNA amplification.

African trypanosome species were identified using the Polymerase Chain Reaction (PCR) by targeting repetitive DNA for amplification. Using oligonucleotide primers designed to anneal specifically to the satellite DNA monomer of each species/subgroup, we were able to accurately identify Trypanosoma simiae, three subgroups of T. congolense, T. brucei and T. vivax. The assay was sensitive and specific, detecting one trypanosome unequivocally and showing no reaction with non-target trypanosome DNA or a huge excess of host DNA. The assay was used to identify developmental stage trypanosomes in the tsetse fly. The use of radioisotopes was not necessary and mixed infections could be detected easily by incorporating more than one set of primers in a single reaction. The use of crude preparations of template made the process very rapid. The methodology should be suitable for large-scale epidemiological studies.