Eduardo Fuentes-Contreras

Evaluation of Azinphos-Methyl Resistance and Activity of Detoxifying Enzymes in Codling Moth (Lepidoptera: Tortricidae) from Central Chile

Abstract Regular applications of insecticides have been the main management practice against codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) in Chile. Organophosphates are the most widely used insecticides, and azinphos-methyl is an important element in spray programs. In particular, we evaluated diagnostic doses of azinphos-methyl on neonate and postdiapausing larvae from seven apple (Malus spp.) orchards. We also evaluated the activity of detoxifying enzymes, such as glutathione S-transferases (GSTs), cytochrome P450 polysubstrate monooxygenases (PSMOs), and esterases, which are likely to be involved in resistance to insecticides. Such responses were compared with an insecticide-susceptible strain that has been maintained in the laboratory for several years. Neonate larval mortality of field populations to azinphos-methyl was not significantly different from of the susceptible strain. In contrast, postdiapause larval mortality was significantly lower in the six analyzed populations than in the susceptible strain. The C. pomonella populations with reduced postdiapause mortality to azinphos-methyl also showed statistically higher GST activity. Finally, no significant differences were found in total esterase or PSMO activity between C. pomonella populations. Therefore, the observed reduction in postdiapause larval mortality to azinphos-methyl seems to be associated with an increase in GST activity.

PSEUDOREPLICATION AND ITS FREQUENCY IN OLFACTOMETRIC LABORATORY STUDIES

The evaluation of behavioral responses of an organism to a particular stimulus normally implies the design of a bioassay. Measurements of the response in a number of replicates are necessary to perform inferential statistics and therefore accept or reject a hypothesis about the effect of the stimulus on the behavior of the organism under study. In the present article, we address the importance of pseudoreplication in studies of chemical ecology, particularly in laboratory experiments on olfactory responses of insects to semiochemicals in olfactometers and wind tunnels. Pseudoreplication may be caused by lack of independence in the stimulus or the experimental device, the reutilization of test insects, or the use of groups of test insects, without adequate statistical analysis addressing such dependency. Each and all of the cases reviewed (N = 105) lacked information in at least one of the factors listed above; hence no cases could be said with certainty to be free of pseudoreplication. Forty-nine cases (46.7%) contained explicit information revealing that pseudoreplication existed in terms of one or more of the criteria listed above; in only three of these cases did the authors address statistically the stated dependence of the samples. Pseudoreplication due to different factors ranged from 2% to 30% of the cases, with an average of 13%. The most frequent sources of pseudoreplication were the reuse of the device and the use of groups of test insects. The analysis showed the low importance given to obtaining independent replicates in bioassays involving olfactometric responses of insects to semiochemicals.

Population Genetic Structure of Codling Moth (Lepidoptera: Tortricidae) from Apple Orchards in Central Chile

Abstract Codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), is the main pest of pome fruits worldwide. Despite its economic importance, little is known about the genetic structure and patterns of dispersal at the local and regional scale, which are important aspects for establishing a control strategy for this pest. An analysis of genetic variability using microsatellites was performed for 11 codling moth populations in the two major apple (Malus domestica Borkh) cropping regions in central Chile. Despite the geographical distances between some populations (≈185 km), there was low genetic differentiation among populations (FST = 0.002176), with only slight isolation by distance. Only ≈0.2% of the genetic variability was found among the populations. Geographically structured genetic variation was independent of apple orchard management (production or abandoned). These results suggest a high genetic exchange of codling moth between orchards, possibly mediated by human activities related to fruit production.

The invasion route for an insect pest species: the tobacco aphid in the New World

Biological invasions are rapid evolutionary events in which populations are usually subject to a founder event during introduction followed by rapid adaptation to the new environment. Molecular tools and Bayesian approaches have shown their utility in exploring different evolutionary scenarios regarding the invasion routes of introduced species. We examined the situation for the tobacco aphid, Myzus persicae nicotianae, a recently introduced aphid species in Chile. Using seven microsatellite loci and approximate Bayesian computation, we studied populations of the tobacco aphid sampled from several American and European countries, identifying the most likely source populations and tracking the route of introduction to Chile. Our population genetic data are consistent with available historical information, pointing to an introduction route of the tobacco aphid from Europe and/or from other putative populations (e.g. Asia) with subsequent introduction through North America to South America. Evidence of multiple introductions to North America from different genetic pools, with successive loss of genetic diversity from Europe towards North America and a strong bottleneck during the southward introduction to South America, was also found. Additionally, we examined the special case of a widespread multilocus genotype that was found in all American countries examined. This case provides further evidence for the existence of highly successful genotypes or ‘superclones’ in asexually reproducing organisms.

Genetic diversity and insecticide resistance of Myzus persicae (Hemiptera: Aphididae) populations from tobacco in Chile: evidence for the existence of a single predominant clone

The tobacco-feeding race of Myzus persicae (Sulzer), formerly known as M. nicotianae Blackman, was introduced into Chile during the last decade. In order to evaluate the genetic diversity and insecticide resistance status of Chilean tobacco aphid populations, a field survey was conducted in 35 tobacco fields covering a 300 km latitudinal survey. The populations sampled were characterized using microsatellite markers and morphometric multivariate analysis. Insecticide resistance levels were assessed through a microplate esterase assay and the mutation status of the kdr gene. All samples collected corresponded to the same anholocyclic aphid genotype, and showed morphological variation within the range expected for the tobacco-feeding race of M. persicae. Esterase activity showed the level and variability expected for an R1 clone lacking mutations in the sodium channels (susceptible kdr), thus corresponding to a type slightly resistant to organophosphate and carbamate, and susceptible to pyrethroid insecticides.

Behavioural differences between Aphidius ervi populations from two tritrophic systems are due to phenotypic plasticity

The Palaeoarctic parasitoid Aphidius ervi Haliday (Hymenoptera, Aphidiidae) parasitises legume aphids in its region of origin. In Chile, it parasitises both legume and cereal aphids. This special situation was studied at two levels: (i) the host searching behaviour of A. ervi from two different tritrophic systems (Acyrthosiphon pisum on alfalfa and Sitobion avenae on wheat) was investigated in dual choice tests in a wind tunnel between odours from both A. pisum‐alfalfa host plant complex (HPC) and S. avenae‐wheat HPC, and (ii) the genetic structure of A. ervi populations from both sources using molecular markers. Responses of A. ervi females to volatile olfactory cues emanating from A. pisum‐alfalfa HPC and S. avenae‐wheat HPC were significantly higher towards the HPC on which they were reared during the last generation before experimentation, regardless of the origin of the parasitoid. As previously described for this parasitoid species, oviposition experience was also of major relevance in the preferences of female parasitoids. On the other hand, variation in mitochondrial DNA segments and RAPD‐PCR polymorphism using total DNA showed the absence of host‐based population structure and a high genetic homogeneity between these A. ervi populations. These results reject the possible existence of different host‐strains of this parasitoid in Chile.

Evaluating reproductive fitness and metabolic costs for insecticide resistance in Myzus persicae from Chile

The development of insecticide resistance in pest insects is an increasing problem for agriculture, forestry and public health. Aphids are ubiquitous herbivorous insects, with approximately 4700 known species, of which less than 5% exploit the agricultural environment successfully. Of these, the peach‐potato aphid Myzus persicae Sulzer is recognized as one of the most important pests worldwide because it has acquired resistance to many insecticides. Although resistance to insecticides provides important benefits for pests in agricultural fields that are treated with insecticides, it may be associated with fitness (or other) costs in environments that are insecticide free. In the present study, the fitness and energy costs that might be experienced by M. persicae in an insecticide‐free environment when carrying at least one insecticide resistance mutation (IRM), or by having an increased production of esterases, are evaluated. The study investigates whether genotypes that have an IRM also have enhanced esterase production, whether there is any metabolic cost associated with insecticide resistance, and whether there are any fitness costs associated with insecticide resistance and metabolic expenditure. The intrinsic rate of increase, standard metabolic rate (i.e. a measure of maintenance costs) and constitutive esterase activity are determined for 30 different multilocus genotypes carrying (or not carrying) at least one of the two most frequent insecticide resistance mutations (MACE and kdr/super‐kdr) that occur in Chile. The results show that genotypes carrying at least one IRM have higher levels of total esterase activity than genotypes without an IRM, that there is no evidence of an energy cost associated with total esterase activity or IRM, and no evidence for a reproductive fitness cost associated with total esterase activity, IRM or metabolic rate. The results agree with previous studies showing linkage disequilibrium between insecticide resistance mechanisms, although they contrast with those of studies that report fitness costs associated with insecticide resistance in Myzus persicae.

Susceptibilidad a Insecticidas y Actividad Enzimática de Cydia pomonella L. (Lepidoptera: Tortricidae) Proveniente de Tres Huertos de la Región del Maule, Chile

Cydia pomonella L., la principal plaga de pomaceas y nogales en Chile, ha sido controlada casi exclusivamente con aplicaciones de insecticidas organofosforados. Sin embargo, durante las ultimas temporadas se han observado crecientes niveles de frutos danados a cosecha. Dado que esta plaga ha desarrollado resistencia a insecticidas en varios paises, se evaluo la susceptibilidad a dosis diagnostico de azinfos metil y tebufenozide de larvas diapausantes provenientes de tres huertos de manzano de la Region del Maule y una cepa susceptible de referencia (S); ademas de la actividad de enzimas detoxificadoras en adultos emergidos de las mismas Tanto la actividad de oxidasas de funcion multiple (OFM) como de glutation-S-transferasas (GST) se evaluo a traves de fluorimetria, mientras la de esterasas (EST) se determino por absorbancia. La mortalidad larvaria frente a azinfos metil fue significativamente menor para Molina y Teno (30 y 85,4%, respectivamente) que para la cepa S (95,3%). Para tebufenozide la mortalidad larvaria fue significativamente menor en Molina (35,31%) que en la cepa S (88,6%). La actividad de GST fue significativamente mayor en dos de los tres huertos analizados (Teno = 13.679 unidades de fluorescencia insecto-1 y Molina =13.096 unidades de fluorescencia insecto-1). Similarmente, la actividad de OFM fue significativamente mayor en los mismos huertos, con valores 25,08 y 17,95 picogramos (pg) de 7OH insecto-1 min.-1 para Molina y Teno, respectivamente. La cepa S presento una actividad de EST significativamente mayor que la de las otras poblaciones, la cual parece no estar relacionada con la menor susceptibilidad a los insecticidas evaluados.

Landscape Analysis of Adult Codling Moth (Lepidoptera: Tortricidae) Distribution and Dispersal within Typical Agroecosystems Dominated by Apple Production in Central Chile

ABSTRACT We analyzed the spatial distribution and dispersal of codling moth, Cydia pomonella (L.), adults within two heterogeneous agroecosystems typical of central Chile: commercial apple, Malus domestica Borkhausen, orchards surrounded by various unmanaged host plants. Both a geostatistical analysis of catches of adult males with a grid of sex pheromone-baited traps and an immunological self-marking technique combined with traps baited with a male and female attractant were used. The spatial analyses identified the key sources of moths within these diverse landscapes. Codling moth catches in traps were spatially associated within distances of ≈150–300 m. Similarly, the mean distance from the immunological self-marking plots within the commercial apple orchard to the traps that captured marked adults was 282 m. In contrast, the mean distance in the capture of marked moths from unmanaged self-marking plots to a commercial orchard was 828 m. These data suggest that the success of any future areawide management programs for codling moth in Chilean pome fruit must include a component for managing or removing noncommercial hosts that surround orchards. This analysis also suggests that the selection pressure for resistance imposed by insecticide sprays within managed orchards is likely dampened by the influx of susceptible moths from unmanaged sites common in central Chile.

Landscape composition modulates population genetic structure of Eriosoma lanigerum (Hausmann) on Malus domestica Borkh in central Chile

Landscape genetics have been particularly relevant when assessing the influence of landscape characteristics on the genetic variability and the identification of barriers to gene flow. Linking current practices of area-wide pest management information on pest population genetics and geographical barriers would increase the efficiency of these programs. The woolly apple aphid, Eriosoma lanigerum (Hausmann), an important pest of apple orchards worldwide, was collected on apple trees (Malus domestica Borkh) from different locations in a 400 km north-south transect trough central Chile. In order to determine if there was population structure, diversity and flow were assessed. A total of 215 individuals from these locations were analysed using Inter Simple Sequence Repeat (ISSR) markers. Four ISSR primers generated a total of 114 polymorphic loci. The percentage of molecular variation among locations was 18%. As the algorithm used by structure may be poorly suited for inferring the number of genetic clusters in a data set that has an IBD relationship, the number of genetic clusters in the samples was also analyzed using a Bayesian clustering method implemented in software Baps version 4.14. We inferred the presence of four genetic clusters in the study region. Clustering of individuals followed a pattern explained by some geographical barriers. Using partial Mantel tests, we detected barriers to gene flow other than distance, created by a combination of main rivers and mountains. Although landscape genetics are rarely used in pest management, our results suggest that these tools may be suitable for the design of area-wide pest management programs.