Blas Lavandero

The need for effective marking and tracking techniques for monitoring the movements of insect predators and parasitoids

Predators and parasitoids move through the landscape at a wide range of rates and over a broad range of spatial scales. Understanding the dispersal characteristics of such beneficials is of crucial importance for classical, augmentative, inundative and conservation biological control. It is a key practice, following the release of classical (exotic) and augmentative (indigenous) biological control agents, to assess whether they have become successfully established, and also to what extent the agent has spread from the release points. It is important in conservation biological control to understand the role that natural enemy movements play in the improvement of pest control achieved through the provision of pollen, nectar, shelter and/or alternative prey/hosts. Other aspects of predator and parasitoid movement pertinent to biological control are the role refugia play in influencing, via natural enemy movements, control of pest population numbers. In these areas and others, some form of marking and/or tracking of insect predators and parasitoids is usually required so that movements can be studied. This special issue considers the usefulness and limitations of marking and tracking techniques, through up-to-date reviews written by an international team of researchers who are actively involved in the study of predator and parasitoid ecology.

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.

Genetic structure of highland papayas (Vasconcellea pubescens (Lenné et C. Koch) Badillo) cultivated along a geographic gradient in Chile as revealed by Inter Simple Sequence Repeats (ISSR)

In Chile Vasconcellea pubescens is cropped to produce canned fruit, juice, jam and processed sweets. Additionally this species produces latex with a high level of papain, an important and valuable proteolytic enzyme with industrial applications. In this investigation seven ISSR primers were used to study the level and organization of genetic diversity in 333 samples of V. pubescens. Out of the 114 bands recorded, 63 proved to be polymorphic (Pxa0=xa055.3%). At the species level, the genetic diversity was rather low (hxa0=xa00.01xa0±xa06,80188E-05, Shannon’s Index Ixa0=xa00.16xa0±xa00,000148). The major portion of the genetic diversity was found within groups (65%). The genetic differentiation between the different groups was significant, as the AMOVA analysis suggested (Φptxa0=xa00.35). When analysing the Northern area alone, the differentiation increased to Φptxa0=xa00.40. When only the Southern area was analysed, Φpt decreased to 0.18, indicating greater genetic similarity among the samples. The results generated from Structure and Bayesian Analysis of Population Structure distinguished 8 genetically different groups, five of them located in the north and three in the south. The results are discussed in the light of the growers’ practices.

Estimating Gene Flow between Refuges and Crops: A Case Study of the Biological Control of Eriosoma lanigerum by Aphelinus mali in Apple Orchards

Parasitoid disturbance populations in agroecosystems can be maintained through the provision of habitat refuges with host resources. However, specialized herbivores that feed on different host plants have been shown to form host-specialized races. Parasitoids may subsequently specialize on these herbivore host races and therefore prefer parasitizing insects from the refuge, avoiding foraging on the crop. Evidence is therefore required that parasitoids are able to move between the refuge and the crop and that the refuge is a source of parasitoids, without being an important source of herbivore pests. A North-South transect trough the Chilean Central Valley was sampled, including apple orchards and surrounding Pyracantha coccinea (M. Roem) (Rosales: Rosacea) hedges that were host of Eriosoma lanigerum (Hemiptera: Aphididae), a globally important aphid pest of cultivated apples. At each orchard, aphid colonies were collected and taken back to the laboratory to sample the emerging hymenopteran parasitoid Aphelinus mali (Hymenoptera: Aphelinidae). Aphid and parasitoid individuals were genotyped using species-specific microsatellite loci and genetic variability was assessed. By studying genetic variation, natural geographic barriers of the aphid pest became evident and some evidence for incipient host-plant specialization was found. However, this had no effect on the population-genetic features of its most important parasitoid. In conclusion, the lack of genetic differentiation among the parasitoids suggests the existence of a single large and panmictic population, which could parasite aphids on apple orchards and on P. coccinea hedges. The latter could thus comprise a suitable and putative refuge for parasitoids, which could be used to increase the effectiveness of biological control. Moreover, the strong geographical differentiation of the aphid suggests local reinfestations occur mainly from other apple orchards with only low reinfestation from P. cocinnea hedges. Finally, we propose that the putative refuge could act as a source of parasitoids without being a major source of aphids.

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.

Migration of coccinellids to alfalfa fields with varying adjacent vegetation in Central Chile.

Permanent and permeable edges, where natural enemies can feed, overwinter or easily cross over, should enhance the early arrival of these predators to crops. We evaluated the abundance and species richness of coccinellids migrating to alfalfa fields adjacent to Eucalyptus , a mix of false acacia, blackberries and poplar (F-B-P), vineyards, corn and annual vegetables. From September 2007 to May 2008, we captured coccinellids in three sticky traps (2.64 m2) placed at the borders between alfalfa fields and adjacent vegetation. We also estimated the abundance of aphid populations in the alfalfa fields, by counting the number of individuals per alfalfa stem in spring, summer and autumn. We collected 90,396 coccinellids from 14 species. Neither total abundance nor species richness of coccinellids was significantly affected by adjacent vegetation, but Adalia deficiens , Psyllobora picta and Cycloneda sanguinea were more abundant in alfalfa adjacent to Eucalyptus and F-B-P, meanwhile Olla v-nigrum next to annual crops and Hyperaspis sphaeridioides next to vineyards. Edge height and orientation explained 94% of the variance in species abundance. Particularly, P. picta and O. v-nigrum were positively and negatively influenced by border height, respectively. Hyperaspis sphaeridioides was negatively affected by northern exposure and none of the species was affected by edge permeability. Aphids were less abundant in alfalfa fields adjacent to F-B-P, especially in spring. These results show that most species of coccinellids were not affected by the composition of crop edges, although tall permanent edges may enhance the arrival of particular coccinellid species to alfalfa fields. Bordes permanentes y permeables favorecerian la llegada de los enemigos naturales a los cultivos. Se evaluo la abundancia y riqueza de especies de coccinelidos migrando a campos de alfalfa adyacentes a Eucalyptus , una mezcla de Falsa acacia, zarzamoras y alamos (F-B-P), vinas, maiz y cultivos anuales bajos. Tambien se estimo la abundancia de afidos en los campos de alfalfa. Entre septiembre 2007 y mayo 2008, los coccinelidos fueron capturados en tres trampas pegajosas (2,64 m2) ubicadas en el borde de cada alfalfal; la abundancia de afidos dentro de los alfalfales se estimo en primavera, verano y otono. Se colectaron 90.396 coccinelidos de 14 especies. Ni la abundancia total ni la riqueza de especies de coccinelidos fueron significativamente afectados por el tipo de vegetacion adyacente, pero Adalia deficiens , Psyllobora picta y Cycloneda sanguinea fueron mas capturadas en campos de alfalfa adyacentes a Eucalyptus y F-B-P, Olla v-nigrum cerca de cultivos anuales e Hyperaspis sphaeridioides cerca de vinas. La altura y orientacion de los bordes explican el 94% de la varianza de la abundancia de especies. Psyllobora picta fue positivamente influenciada por la altura, O. v-nigrum negativamente e Hyperaspis sphaeridioides negativamente afectada por la exposicion norte; ninguna de las especies fue afectada por la permeabilidad del borde. Los afidos fueron menos abundantes en alfalfales cercanos a F-B-P. En general, la mayoria de las especies de coccinelidos no fueron afectadas por el tipo de borde, pero los bordes altos y permanentes facilitan la llegada de algunas especies de coccinelidos a los campos de alfalfa.

Genotype matching in a parasitoid–host genotypic food web: an approach for measuring effects of environmental change

Food webs typically quantify interactions between species, whereas evolution operates through the success of alleles within populations of a single species. To bridge this gap, we quantify genotypic interaction networks among individuals of a single specialized parasitoid species and its obligate to cyclically parthenogenetic aphid host along a climatic gradient. As a case study for the kinds of questions genotype food webs could be used to answer, we show that genetically similar parasitoids became more likely to attack genetically similar hosts in warmer sites (i.e. there was network‐wide congruence between the within‐species shared allelic distance of the parasitoid and that of its host). Narrowing of host‐genotype‐niche breadth by parasitoids could reduce resilience of the network to changes in host genetic structure or invasion by novel host genotypes and inhibit biological control. Thus, our approach can be easily used to detect changes to sub‐species‐level food webs, which may have important ecological and evolutionary implications, such as promoting host‐race specialization or the accelerated loss of functional diversity following extinctions of closely related genotypes.

Diversity, frequency and geographic distribution of facultative bacterial endosymbionts in introduced aphid pests.

Facultative bacterial endosymbionts in insects have been under intense study during the last years. Endosymbionts can modify the insects phenotype, conferring adaptive advantages under environmental stress. This seems particularly relevant for a group of worldwide agricultural aphid pests, because endosymbionts modify key fitness‐related traits, including host plant use, protection against natural enemies and heat tolerance. Aimed to understand the role of facultative endosymbionts on the success of introduced aphid pests, the distribution and abundance of 5 facultative endosymbionts (Hamiltonella defensa, Regiella insecticola, Serratia symbiotica, Rickettsia and Spiroplasma) were studied and compared in 4 cereal aphids (Sitobion avenae, Diuraphis noxia, Metopolophium dirhodum and Schizaphis graminium) and in the pea aphid Acyrthosiphon pisum complex from 2 agroclimatic zones in Chile. Overall, infections with facultative endosymbionts exhibited a highly variable and characteristic pattern depending on the aphid species/host race and geographic zone, which could explain the success of aphid pest populations after their introduction. While S. symbiotica and H. defensa were the most frequent endosymbionts carried by the A. pisum pea‐race and A. pisum alfalfa‐race aphids, respectively, the most frequent facultative endosymbiont carried by all cereal aphids was R. insecticola. Interestingly, a highly variable composition of endosymbionts carried by S. avenae was also observed between agroclimatic zones, suggesting that endosymbionts are responding differentially to abiotic variables (temperature and precipitations). In addition, our findings constitute the first report of bacterial endosymbionts in cereal aphid species not screened before, and also the first report of aphid endosymbionts in Chile.

Does sex-biased dispersal account for the lack of geographic and host-associated differentiation in introduced populations of an aphid parasitoid?

Host recognition and use in female parasitoids strongly relies on host fidelity, a plastic behavior which can significantly restrict the host preferences of parasitoids, thus reducing the gene flow between parasitoid populations attacking different insect hosts. However, the effect of migrant males on the genetic differentiation of populations has been frequently ignored in parasitoids, despite its known impact on gene flow between populations. Hence, we studied the extent of gene flow mediated by female and male parasitoids by assessing sibship relationships among parasitoids within and between populations, and its impact on geographic and host-associated differentiation in the aphid parasitoid Aphidius ervi. We report evidences of a high gene flow among parasitoid populations on different aphid hosts and geographic locations. The high gene flow among parasitoid populations was found to be largely male mediated, suggested by significant differences in the distribution of full-sib and paternal half-sib dyads of parasitoid populations.

Genetic variability and structure of Gomortega keule (Molina) Baillon (Gomortegaceae) relict populations: geographical and genetic fragmentation and its implications for conservation

Gomortega keule (Molina) Baillon is a rare Chilean species classified as endangered and currently under conser- vation. Currently, conservation of this species is carried out by private companies and government agencies, but is done so based more on pragmatic criteria than scientifically based strategies. In this context, information concerning the genetic variability of the species among the different populations over its entire distribution range is incomplete, making it difficult to coordinate management and conservation strategies. Here we report a study to evaluate the genetic variability and popu- lation structure of G. keule over its entire distribution in Chile. Twenty-five ISSR primers for 223 individuals from 11 geo- graphical populations were tested to evaluate genetic variability. Results showed a high level of genetic diversity for the species. A high level of genetic differentiation among populations was found, while genetic structure of the geographic populations was also shown by using STRUCTURE 2.1 software. Despite the fact that this species has been highly af- fected by human intervention and habitat destruction, a high level of genetic diversity was present. A likely explanation for this is that it reflects the previous distribution of this long-lived species and the current lack of sexual regeneration. Ge- netic diversity data must be considered in the development of a management strategy for further developing the protected areas, for identifying isolated small populations for conservation, and using larger populations with higher genetic diversity as seed sources for ex situ propagation and replanting.