Biological control is widely successful at controlling pests, but effective biocontrol agents are now more difficult to import from countries of origin due to more restrictive international trade laws (the Nagoya Protocol). Coupled with increasing demand, the efficacy of existing and new biocontrol agents needs to be improved with genetic and genomic approaches. Although they have been underutilised in the past, application of genetic and genomic techniques is becoming more feasible from both technological and economic perspectives. We review current methods and provide a framework for using them. First, it is necessary to identify which biocontrol trait to select and in what direction. Next, the genes or markers linked to these traits need be determined, including how to implement this information into a selective breeding program. Choosing a trait can be assisted by modelling to account for the proper agro‐ecological context, and by knowing which traits have sufficiently high heritability values. We provide guidelines for designing genomic strategies in biocontrol programs, which depend on the organism, budget, and desired objective. Genomic approaches start with genome sequencing and assembly. We provide a guide for deciding the most successful sequencing strategy for biocontrol agents. Gene discovery involves quantitative trait loci analyses, transcriptomic and proteomic studies, and gene editing. Improving biocontrol practices includes marker‐assisted selection, genomic selection and microbiome manipulation of biocontrol agents, and monitoring for genetic variation during rearing and post‐release. We conclude by identifying the most promising applications of genetic and genomic methods to improve biological control efficacy.

All hymenopterans (bees, ants, wasps, and sawflies) have haplodiploid sex determination. Generally, this involves haploid males developing from unfertilized eggs and diploid females developing from fertilized eggs, but diploid male production (DMP) frequently occurs. Some species have complementary sex determination (CSD), in which heterozygotes of a csd locus or loci are diploid females, hemizygotes are haploid males, and homozygotes are typically sterile diploid males. These diploid males underlie the diploid male vortex (DMV), the phenomenon of inbreeding reducing csd allelic diversity and causing increasingly higher production of sterile diploid males until the population dies out. The DMV has been cited as an extinction risk for many species across the order and a danger to both human‐controlled and natural hymenopteran populations important in biological control, pollination, and endangered species conservation. However, it has been unclear how frequently it occurs. We review the known mechanisms for DMV avoidance. Many of these mechanisms are linked to lifestyle, and so we structure our investigation around eusocial lifestyle and non‐eusocial (solitary or gregarious) species. We also review documented DMV incidence to make an inference about its prevalence. There are many means to avoid inbreeding or diploid male production, including eusocial‐exclusive polygyny, polyandry, and diploid queen execution. For both eusocial and non‐eusocial species these include biological mechanisms such as multi‐locus CSD or non‐CSD sex determination, diploid male inviability or brood removal, partial diploid male fecundity, and mating avoidance of kin or diploid males; or population genetic mechanisms such as gene flow and dispersal, balancing selection of csd alleles (with some being more prominent in eusocial vs. non‐eusocial species). Documented cases of DMV are uncommon, and incidence is often tied to exacerbatory conditions such as habitat fragmentation and host declines. With this review we suggest that due to numerous avoidance mechanisms, DMV risk may not be as high as previously believed, and requires specific circumstances. In doing so we aim to better inform hymenopteran breeding and conservation efforts.

In hymenopterans, males are normally haploid (1n) and females diploid (2n), but individuals with divergent ploidy levels are frequently found. In species with ‘complementary sex determination’ (CSD), increasing numbers of diploid males that are often infertile or unviable arise from inbreeding, presenting a major impediment to biocontrol breeding. Non‐CSD species, which are common in some parasitoid wasp taxa, do not produce polyploids through inbreeding. Nevertheless, polyploidy also occurs in non‐CSD Hymenoptera. As a first survey on the impacts of inbreeding and polyploidy of non‐CSD species, we investigate life‐history traits of a long‐term laboratory line of the parasitoid Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) (‘Whiting polyploid line’) in which polyploids of both sexes (diploid males, triploid females) are viable and fertile. Diploid males produce diploid sperm and virgin triploid females produce haploid and diploid eggs. We found that diploid males did not differ from haploid males with respect to body size, progeny size, mate competition, or lifespan. When diploid males were mated to many females (without accounting for mating order), the females produced a relatively high proportion of male offspring, possibly indicating that these males produce less sperm and/or have reduced sperm functionality. In triploid females, parasitization rate and fecundity were reduced and body size was slightly increased, but there was no effect on lifespan. After one generation of outbreeding, lifespan as well as parasitization rate were increased, and a body size difference was no longer apparent. This suggests that outbreeding has an effect on traits observed in an inbred polyploidy background. Overall, these results indicate some phenotypic detriments of non‐CSD polyploids that must be taken into account in breeding.

Recurrent polyploidization occurred in the evolutionary history of most Eukaryota. However, how neopolyploid detriment (sterility, gigantism, gene dosage imbalances) has been overcome and even been bridged to evolutionary advantage (gene network diversification, mass radiation, range expansion) is largely unknown, particularly for animals. We used the parasitoid wasp Nasonia vitripennis, a rare insect system with heritable polyploidy, to begin addressing this knowledge gap. In Hymenoptera the sexes have different ploidies (haploid males, diploid females) and neopolyploids (diploid males, triploid females) occur for various species. Although such polyploids are usually sterile, those of N. vitripennis are reproductively capable and can even establish stable polyploid lines. To assess the effects of polyploidization, we compared a long-established polyploid line, the Whiting polyploid line (WPL) and a newly generated transformer knockdown line (tKDL) for fitness traits, absolute gene expression, and cell size and number. WPL polyploids have high male fitness and low female fecundity, while tKDL polyploids have poor male mate competition ability and high fertility. WPL has larger cells and cell number reduction, but the tKDL does not differ in this respect. Expression analyses of two housekeeping genes indicated that gene dosage is linked to sex irrespective of ploidy. Our study suggests that polyploid phenotypic variation may explain why some polyploid lineages thrive and others die out; a commonly proposed but difficult-to-test hypothesis. This documentation of diploid males (tKDL) with impaired competitive mating ability; triploid females with high fitness variation; and hymenopteran sexual dosage compensation (despite the lack of sex chromosomes) all challenges general assumptions on hymenopteran biology. We conclude that polyploidization is dependent on the duplicated genome characteristics and that genomes of different lines are unequally suited to survive diploidization. These results demonstrate the utility of N. vitripennis for delineating mechanisms of animal polyploid evolution, analogous to more advanced polyploid plant models.

There is growing interest in trait selection for the improvement of insect biological control. Constraints from the Nagoya Protocol for sourcing novel biocontrol agents (BCAs) make optimization of accessible populations a higher priority. However, the effectiveness of selection programs remains unclear. This requires knowing whether biocontrol traits are heritable and whether captive populations have sufficient genetic variation for selection. To address this knowledge gap, we systematically reviewed reported values of broad‐sense heritability (H²), narrow‐sense heritability (h²), and evolvability (CV_a) for insect biocontrol traits, providing an overview of the potential for their genetic improvement while identifying the irregularities in the reporting of heritability data across studies. Our algorithmic search string focused on studies working with arthropod BCAs widely used in augmentative biocontrol and/or permitted for use in the EPPO region (European and Mediterranean Plant Protection Organization). Five thousand two hundred and nine initial search hits from the CAB Abstracts (n = 2321) and BIOSIS (n = 3442) databases recovered 277 relevant papers after screening, 94 of which included estimation methods and reported biocontrol traits as being heritable. However, over half (52) of these papers did not report any H², h², or CV_a values. There was strong indication of genetic variation (e.g., h² > 0.2) for numerous traits. Most data focused on pest suppression ability and mass reproduction, while little was reported on abiotic/biotic adaptation or ecological risk, despite their importance for biocontrol success. Contrary to expectations, heritabilities for complex life‐history traits were equally high as those for morphology, whereas the heritability of insecticide resistance was relatively low. Despite relatively few data points and a large value range, this review demonstrates good potential for artificial selection of biocontrol traits and provides a single resource for collated data. We make recommendations for more consistent and expansive collection and repository of biocontrol trait data and to revise the Nagoya Protocol to facilitate breeding programs.

Host race formation and speciation are at the core of the enormous insect diversification. Insect–host relationships can take many forms, ranging from parasitic to mutualistic. Despite its long history of study, many questions remain about host race formation and speciation. They are addressed in eight original papers of this special issue, including two review‐type articles. In line with the scope of Entomologia Experimentalis et Applicata, they include both fundamental and applied studies. They reveal that host race formation and speciation can take many forms and that they are still active topics of entomological research.