Incongruent nuclear and mitochondrial genetic structure of new world screwworm fly populations due to positive selection of mutations associated with dimethyl- and diethyl-organophosphates resistance

Molecular basis of resistance to organophosphate insecticides in the New World screw-worm fly

Background

The emergence of insecticide resistance is a fast-paced example of the evolutionary process of natural selection. In this study, we investigated the molecular basis of resistance in the myiasis-causing fly Cochliomyia hominivorax (Diptera: Calliphoridae) to dimethyl-organophosphate (OP) insecticides.

Methods

By sequencing the RNA from surviving larvae treated with dimethyl-OP (resistant condition) and non-treated larvae (control condition), we identified genes displaying condition-specific polymorphisms, as well as those differentially expressed.

Results

Both analyses revealed that resistant individuals have altered expression and allele-specific expression of genes involved in proteolysis (specifically serine-endopeptidase), olfactory perception and cuticle metabolism, among others. We also confirmed that resistant individuals carry almost invariably the Trp251Ser mutation in the esterase E3, known to confer OP and Pyrethroid resistance. Interestingly, genes involved in metabolic and detoxifying processes (notably cytochrome P450s) were found under-expressed in resistant individuals. An exception to this were esterases, which were found up-regulated.

Conclusions

These observations suggest that reduced penetration and aversion to dimethyl-OP contaminated food may be important complementary strategies of resistant individuals. The specific genes and processes found are an important starting point for future functional studies. Their role in insecticide resistance merits consideration to better the current pest management strategies.

Genetic Differentiation of a New World Screwworm Fly Population from Uruguay Detected by SNPs, Mitochondrial DNA and Microsatellites in Two Consecutive Years

The New World screwworm (NWS) fly, Cochliomyia hominivorax (Diptera: Calliphoridae), is an economically important ectoparasite currently distributed in South America and in the Caribbean basin. The successful eradication of this species in USA, Mexico and continental Central America was achieved by a control program based on the sterile insect technique (SIT). In order to implement a genetic control strategy over the NWS fly's current area of occurrence, first, it is necessary to understand the species dynamics and population structure. In order to address this objective, the spatial genetic structure of the NWS fly was previously reported in South America based on different genetic markers; however, to date, no study has investigated temporal changes in the genetic composition of its populations. In the current study, the temporal genetic structure of a NWS fly population from Uruguay was investigated through two consecutive samplings from the same locality over an interval of approximately 18 generations. The genetic structure was accessed with neutral and under selection SNPs obtained with genotyping-by-sequencing. The results gathered with these data were compared to estimates achieved with mitochondrial DNA sequences and eight microsatellite markers. Temporal changes in the genetic composition were revealed by all three molecular markers, which may be attributed to seasonal changes in the NWS fly's southern distribution. SNPs were employed for the first time for estimating the genetic structure in a NWS fly population; these results provide new clues and perspectives on its population genetic structure. This approach could have significant implications for the planning and implementation of management programs.

A review on the occurrence of Cochliomyia hominivorax (Diptera: Calliphoridae) in Brazil

Cochliomyia hominivorax (Coquerel, 1858), the New World screwworm, causes primary myiasis in wild and domestic animals in tropical and subtropical regions of Brazil. Although this species is considered to occur throughout the country, organized information about its recorded distribution has not been available until now. This article aimed to provide a comprehensive review of the historical and current data published on both immature (myiasis) and adult stages of C. hominivorax in Brazil. A total of 174 articles were found; of these, 141 articles reported myiasis cases in cattle (146 records), humans (68 records), and other mammalian hosts (40 records), and captures of adult flies were reported in 33 articles. C. hominivorax is widespread in Brazil, having been recorded in 208 municipalities in all major biomes of the country.

High Genetic Diversity and No Population Structure of the New World Screwworm Fly Cochliomyia hominivorax (Diptera: Calliphoridae) on a Microgeographic Scale: Implications for Management Units

The New World screwworm fly Cochliomyia hominivorax (Coquerel, 1858) (Diptera: Calliphoridae) is an important livestock pest endemic to the Americas that has been eradicated from North and continental Central America with a control program based on the Sterile Insect Technique (SIT). The establishment of target management units is a strategic step in the implementation of new control programs, which can be achieved using genetic studies of natural populations. Previous studies of New World screwworm fly populations were conducted on the continental scale and identified four main groups: two in South America and two in the Caribbean. However, studies within these groups are needed to determine which smaller geographic areas can be treated as management units. Here, we analyze the genetic variability distribution and the population demographic signals of the New World screwworm fly in a 6,000 km2 area located along the border of Brazil and Uruguay. This area was the subject of the first control pilot program conducted in South America. We studied eight microsatellite loci and sequences from two mitochondrial DNA regions in individuals sampled at 20-25 livestock breeding farms. We observed no population structure and found high genetic variability on the geographical scale sampled for both molecular markers. Our microsatellite data suggest that these populations are not in equilibrium, and demographic analyses based on mitochondrial data indicate population expansion. These results suggest that this geographic scale is not adequate for future New World screwworm fly management in South America.

DNA Barcodes for Forensically Important Fly Species in Brazil

Here, we analyze 248 DNA barcode sequences of 35 fly species of forensic importance in Brazil. DNA barcoding can be effectively used for specimen identification of these species, allowing the unambiguous identification of 31 species, an overall success rate of 88%. Our results show a high rate of success for molecular identification using DNA barcoding sequences and open new perspectives for immature species identification, a subject on which limited forensic investigations exist in Tropical regions. We also address the implications of building a robust forensic DNA barcode database. A geographic bias is recognized for the COI dataset available for forensically important fly species in Brazil, with concentration of sequences from specimens collected mainly in sites located in the Cerrado, Mata Atlântica, and Pampa biomes.

Patterns of genetic variation among geographic and host-plant associated populations of the peach fruit moth Carposina sasakii (Lepidoptera: Carposinidae)

Background

Populations of herbivorous insects may become genetically differentiated because of local adaptation to different hosts and climates as well as historical processes, and further genetic divergence may occur following the development of reproductive isolation among populations. Here we investigate the population genetic structure of the orchard pest peach fruit moth (PFM) Carposina sasakii (Lepidoptera: Carposinidae) in China, which shows distinct biological differences when characterized from different host plants. Genetic diversity and genetic structure were assessed among populations from seven plant hosts and nine regions using 19 microsatellite loci and a mitochondrial sequence.

Results

Strong genetic differentiation was found among geographical populations representing distinct geographical regions, but not in host-associated populations collected from the same area. Mantel tests based on microsatellite loci indicated an association between genetic differentiation and geographical distance, and to a lesser extent environmental differentiation. Approximate Bayesian Computation analyses supported the scenario that PFM likely originated from a southern area and dispersed northwards before the last glacial maximum during the Quaternary.

Conclusions

Our analyses suggested a strong impact of geographical barriers and historical events rather than host plants on the genetic structure of the PFM; however, uncharacterized environmental factors and host plants may also play a role. Studies on adaptive shifts in this moth should take into account geographical and historical factors.

Electronic supplementary material

The online version of this article (10.1186/s12862-017-1116-7) contains supplementary material, which is available to authorized users.

Temporal and Spatial Analysis of the New World Screwworm (Cochliomyia hominivorax) in Darien and Embera, Panama (2001-2011)

Larvae (maggots) of Cochliomyia hominivorax, the New World Screwworm fly, are voracious consumers of living flesh that have a negative economic impact by decreasing productivity, predisposing to other pathogens, and, in severe cases, causing death of domestic livestock. Screwworm caused extensive financial losses to the livestock industry in North America prior to its eradication. Sterile insect technique (SIT) was used to eradicate screwworm throughout North and Central America and continues to be the main tool to control it in eastern Panama. The goal of this study was to evaluate the temporal and spatial trends of screwworm myiasis cases reported in the Province of Darien and Comarca Embera (border with Colombia), Panama, from 2001 to 2011. We hypothesized that screwworm cases would vary seasonally and be spatially clustered near Colombia as a result of effective eradication strategies in Panama and the presence of an autochthonous population of flies in western Colombia. Temporal and spatial data were retrieved from COPEG-USDA records (Panama) and analysed by anova, Ripley's K function, discrete Poisson spatial statistic scan and Getis-Ord Gi*. No significant temporal trend was found, but cases were spatially distributed in four clusters. One cluster of cases occurred from 2001 to 2003 and was considered a focal temporal and spatial cluster. One cluster occurred in 2001 and 2007 indicating more rare outbreaks in an area with fewer cattle. The two remaining clusters contained cases from 2004 to 2011 and 2001 to 2011 suggesting regular breaks in the control barrier due to occasional failures of the SIT programme, difficulties implementing border quarantine strategies, livestock smuggling or the movement of infested wildlife.