It is hard to overemphasize the importance of endosymbionts in arthropod biology, ecology and evolution. Some endosymbionts can complement host metabolic function or provide defence against pathogens; others, such as ubiquitousWolbachiaandCardinium, have evolved strategies to manipulate host reproduction. A common reproductive manipulation strategy is cytoplasmic incompatibility (CI) between differently infected individuals which can result in female mortality or male development of fertilized eggs in haplodiploid hosts. Recently, an additional role of endosymbionts has been recognized in the modification of sex allocation in sexually reproducing haplodiploids. This was theoretically expected due to the maternal inheritance of endosymbionts and natural selection for them to increase infected female production, yet the underlying mechanism remained unknown. Here, we tested whether and howCardiniumandWolbachiacausing different CI types interact to increase female production in a haplodiploid thrips species where sex allocation depends on both maternal condition and egg size provisioning. We found thatCardiniumaugmented female production by increasing maternal fitness and egg size, thereby boosting fertilization rate and offspring fitness.Wolbachia, in contrast, reduced the beneficial effects ofCardinium. Our results demonstrate different invasion strategies and antagonistic effects of endosymbiotic bacteria on host fitness and evolution of sex allocation.

BACKGROUND: The small hive beetle (SHB; Aethina tumida) is a significant pest affecting honey bees and the global beekeeping industry. The harmful effects of chemical pesticides on bee health, non‐target species and ecosystems highlight the need for sustainable SHB control methods. Soil applications of entomopathogenic nematodes (EPNs) targeting the soil‐dwelling life stages (wandering larvae, pupae and emerging adults) of SHB present a promising biological control approach. We conducted comprehensive laboratory experiments to evaluate the biocontrol potential of 32 Australian isolates of five EPN species (Heterorhabditis bacteriophora, Heterorhabditis indica, Heterorhabditis zealandica, Steinernema carpocapsae and Steinernema feltiae) against SHB. We also performed a glasshouse experiment testing the efficacy of nine EPN isolates in soil mesocosms that simulated field conditions.RESULTS: We demonstrated that all isolates caused mortality in all life stages, with wandering larvae the most susceptible, followed by pupae and adults. Notably, H. indica Hi.HRN caused the highest SHB mortality, while S. feltiae Sf.EG was the least effective. These isolates significantly reduced SHB adult emergence, ranging from 9%–93% in autoclaved sterile soil and 16%–59% in natural soil, suggesting interaction with other soil biota. The isolates H. indica Hi.HRN, Hi.LMBT and H. bacteriophora Hb.HIE2 were the most promising candidates for biocontrol, causing >90% corrected SHB mortality in sterile soil and >80% in natural soil. Additionally, soil application of Hi.HRN caused 33% and 43% mortality of SHB adults after their emergence from natural and sterile soils.CONCLUSION: The H. indica isolates Hi.HRN and Hi.LMBT displayed strong biocontrol potential, warranting further evaluation. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The mite Acanthomastix derivatus Katlav & Hajiqanbar sp. nov. (Acari: Prostigmata: Dolichocybidae) is described and illustrated based on females recovered from under elytra of two subcortical beetles, Uloma culinaris (L., 1758) (Coleoptera: Tenebrionidae) and Prostomis sp. (Coleoptera: Prostomidae), which both were collected from decaying stumps in the forests of northern Iran. This finding presents the first record of the genus Acanthomastix from Asia. Furthermore, it is the first record of association between mites of this genus and beetles of the superfamily Tenebrionoidea and also first record of phoretic association between dolichocybid mites and beetles of the family Prostomidae Thomson, 1859 (Tenebrionoidea). A key to world species of the genus Acanthomastix is provided and the distribution and host affiliation of all representatives of this genus are discussed. urn:lsid:zoobank.org:pub:A226E674-601B-4BA6-A170-737405A23EBF