Genetic analyses and occurrence of diploid males in field and laboratory populations of Mastrus ridens (Hymenoptera: Ichneumonidae), a parasitoid of the codling moth

Abstract

The parasitoid wasp Mastrus ridens (Hymenoptera: Ichneumonidae) is a particularly well-suited biological model to document the history and evolution of populations used in classical biological control, repeatedly moved from laboratory to laboratory worldwide and introduced in various environments. This specialist ectoparasitoid of the codling moth was first imported from Kazakhstan to the USA in the 1990's, and then sent to Argentina, Chile and New Zealand. More recently, it was sent to Australia and France from other laboratory colonies, and imported again from field collections in Kazakhstan to Chile. Here, we used DNA sequencing to confirm the taxonomic identity of several populations used for biological control worldwide, and developed microsatellite markers for population genetics studies. A multiplex PCR amplifying 11 polymorphic markers was designed. These markers were used to compare the genetic diversity of laboratory and field populations and evaluate genetic differentiation between them. Results showed that laboratory populations with the longest rearing history had lower genetic diversity. Moreover, the genotyping of males with the markers revealed the occurrence of diploid males, which was further confirmed by flow cytometry, suggesting complementary sex determination (CSD) in this species. The percentage of diploid males in the populations ranged from 4% to 25% and were negatively correlated with diversity indices, which is consistent with a single-locus CSD and genetic bottlenecks in laboratory rearings. Molecular tools proved to be suitable and reliable for genetic diversity analyses in M. ridens, and should be implemented more frequently in classical biological control programs.

Effect of mass rearing on the genetic diversity of the predatory mite Amblyseius swirskii

“…Despite the very high numbers at which commercial A. swirskii populations are reared, genetic diversity can be low if the initial founding population is low (Mackauer, 1976;Bartlett, 1993). Genetic change in mass-reared populations has been described in many arthropods (Nunney, 2003), including experimental populations of D. melanogaster (Woodworth et al, 2002), but also in parasitoids reared for biological control (Guzm an-Larralde et al, 2014; Retamal et al, 2016;Bertin et al, 2017) and various insects reared for 'sterile insect technique' programmes since the 1980s (R€ ossler, 1975;Bush & Neck, 1976;Wong & Nakahara, 1978;Vargas & Carey, 1989). As the field environment is different from the mass-rearing conditions, adaptation to the rearing environment can have a negative impact on the fitness of mass-reared biocontrol agents in the field (Sørensen et al, 2012).…”

Laboratory rearing methods that promote inbreeding have a negative impact on the fitness of Mastrus ridens Horstmann (Hymenoptera: Ichneumonidae), a parasitoid used to control the codling moth

“…Insects forming these populations are individuals descending from field collections made near Almaty, Kazakhstan in 2013 and 2015, and individuals from the mass rearing of the New Zealand colony that were imported to the laboratory in 2014. Insects from the New Zealand colony are descendants of M. ridens collected in the same area in the 1990s by Mills and collaborators (Mills, 2005;Retamal et al, 2016). To maintain M. ridens populations, mated females were provided with Cydia pomonella cocooned fifth instar larvae on pieces of corrugated cardboard, which were replaced every 3 to 7 d with cardboard containing fresh cocooned larvae.…”

“…M a s t r u s r i d e n s H o r s t m a n n ( H y m e n o p t e r a : Ichneumonidae) is an important parasitoid of the codling moth (Cydia pomonella [L.]) in its region of origin (southern Kazakhstan and northwestern China) (Mills, 2005;Retamal et al, 2016). It is a specialist gregarious ectoparasitoid that attacks mature codling moth larvae in their cocoons; it has been used in classical biological control programs against this pest in several countries (Mills, 2005;Devotto et al, 2010;Sandanayaka et al, 2011a;Tortosa et al, 2014) and has the potential for use in augmentation programs.…”

“…It is a specialist gregarious ectoparasitoid that attacks mature codling moth larvae in their cocoons; it has been used in classical biological control programs against this pest in several countries (Mills, 2005;Devotto et al, 2010;Sandanayaka et al, 2011a;Tortosa et al, 2014) and has the potential for use in augmentation programs. Studies carried out in our laboratory indicate that this species displays CSD; colonies with a longer rearing history and more transfers had lower genetic diversity and produced a larger proportion of diploid males (Retamal et al, 2016). The aim of this study was to examine the influence of M. ridens rearing methods, specifically those concerning inbreeding, on several fitness traits to optimize rearing.…”

North-Western Palaearctic species of Pristiphora (Hymenoptera, Tenthredinidae)

“…This can happen if there is no heterozygosity at the complementary sex determination (CSD) locus, preventing female development from a diploid embryo (Naito and Suzuki 1991, Heimpel and de Boer 2008, Harper et al 2016. Survival of diploid males is known in sawflies (Naito and Suzuki 1991, Cook et al 2013, Harper et al 2016 and is common in nature at least in some species of Apocrita (Liebert et al 2005, Retamal et al 2016.…”