Genome-wide analyses of single nucleotide polymorphisms reveal the consequences of traditional mass-rearing on genetic variation in Aphytis melinus (Hymenoptera: Aphelinidae): the danger of putting all eggs in one basket

BACKGROUND: Aphytis melinus DeBach (Hymenoptera: Aphelinidae) is a highly effective biocontrol agent of the California red scale Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae). It is commercially reared and used for augmentative releases within integrated pest management programs. However, mass rearing of biocontrol agents can result in population bottlenecks and high levels of inbreeding and/or adaptation to the factitious rearing conditions. Although these factors can all negatively impact field performance of biocontrol agents, few empirical studies have examined the genetic consequences of mass rearing. We used double-digest RAD sequencing (ddRADseq) to investigate the effect of traditional mass rearing on genetic variation among insectary colonies of A. melinus relative to wild populations in native (Pakistan) and introduced (California) ranges. RESULTS: Analyses of up to 9700 single nucleotide polymorphisms (SNPs) revealed that insectary populations had less genomic variation than introduced populations. This was evidenced by fewer private alleles, reduced heterozygosity, and greater missing data in the insectary populations. Further, California insectaries formed a distinct genomic cluster relative to the other samples, a surprising result given that the insectary colonies were putatively established at different times and from different source populations. These differences were evident across most data sets also after we filtered out contaminant DNA from the most common host species (Aspidiotus nerii Bouché and A. aurantii). CONCLUSION: We hypothesize that this pattern would only result if: (i) directional selection for ‘captive’ phenotypes produces convergent patterns of genomic variation across insectaries; or (ii) the California insectary colonies were all founded from a unifying source population and/or that the insectaries regularly exchange ‘genetic’ stocks. We show that RADseq is an effective method to investigate the effects of mass rearing on genetics of biocontrol agents. © 2019 Society of Chemical Industry.