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Temperature is a major driver of species interactions as it determines many physiological and behavioural parameters of ectothermic organisms such as insects. Examining the effects of elevated temperature and extreme temperature events within and between different trophic levels is crucial for understanding their broader implications for community and ecosystem level processes. We compared parasitism success of two hymenopteran parasitoid species, Diadegma semiclausum and Cotesia vestalis , under different temperature regimes when foraging intra- and interspecifically. Both parasitoid species can be found in the same habitat and are important biological control agents of the cosmopolitan lepidopteran pest Plutella xylostella , the host species in this study. Because parasitoid density may influence parasitism success through interference competition, we first investigated the effect of parasitoid density (one to four females of the same species) on parasitism success at 22 °C. In all assays, parasitoid females were released in cages with a single plant infested with 30 hosts placed in a greenhouse or climate cabinets set at 22, 27 or 33 °C and removed after 3 h. All cages were returned to 22 °C until pupation of the parasitoids or hosts, which were then counted. When females of the same species foraged together, parasitism success increased with parasitoid density. However, when both species were foraging together, parasitism success of D. semiclausum decreased with increasing temperature at both tested densities, whereas the opposite was found for C. vestalis. Nevertheless, parasitism success of D. semiclausum was always higher than that of C. vestalis , irrespective of parasitoid density or temperature, but competitive superiority of D. semiclausum decreased with increasing temperature. Increases in the magnitude and frequency of extreme temperature events under climate change are likely to have differential effects on species involved in intimate interactions, depending on community species composition, as species may differ in thermal resilience. • Temperature affects metabolism, physiology and behaviour of ectothermic organisms. • Temperature effects on host foraging success were studied in two parasitoid species. • Temperature only affected parasitism when the two species foraged interspecifically. • Competitive superiority of the less thermotolerant species decreased with temperature. • Short-term exposure to high temperatures can impact nontrophic interactions. [ABSTRACT FROM AUTHOR]

Abstract Understanding competition between scelionid parasitoids that exploit the same host may provide insight into strategies that allow coexistence on a shared resource. Competition studies typically focus on interactions between native and exotic parasitoids that do not share an evolutionary history; however, coevolved parasitoids may be more likely to demonstrate strategies to avoid or exploit a shared resource. We examined intrinsic and extrinsic competition between Asian Trissolcus japonicus (Ashmead) and T. cultratus (Mayr) (Hymenoptera: Scelionidae) associated with Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) that share an evolutionary history. Interspecific interactions were assessed by providing parasitized egg masses to each species at various intervals post‐parasitism, and measuring host acceptance, developmental suitability, and guarding behaviour. Trissolcus japonicus showed high acceptance of parasitized hosts up to 72 h following oviposition by T. cultratus, despite a very poor developmental outcome. In contrast, T. cultratus generally avoided ovipositing in H. halys eggs containing T. japonicus early‐instar larvae but did not avoid parasitizing H. halys that contained eggs and third instar larvae. The adaptive value of this behaviour was supported by developmental outcome: T. cultratus outcompeted T. japonicus eggs but not early‐instar larvae, and a trophic shift occurred wherein T. cultratus developed as a facultative hyperparasitoid on third instar T. japonicus larvae. Trissolcus japonicus guarded egg masses 8–12× longer and displayed more aggressive interactions than T. cultratus, suggesting T. japonicus is the superior extrinsic competitor. Development as a facultative hyperparasitoid provided a competitive niche for Asian T. cultratus and confirms its instrinsic competitive superiority. This also occurs in a biologically distinct European population of T. cultratus, suggesting that facultative hyperparasitism as a competitive strategy is retained in geographically separated populations that have not coevolved with H. halys or T. japonicus.

BACKGROUND: Interspecific competition in insect parasitoids is an important ecological phenomenon that has relevant implications for biological pest control. To date, interspecific intrinsic (=larval) competition has been intensively studied, while investigations on extrinsic (=adult) competition have often lagged behind. In this study we examined the role played by parasitoid reproductive traits and host clutch size on the outcome of extrinsic competition between Trissolcus basalis (Wollaston) and Ooencyrtus telenomicida (Vassiliev), two egg parasitoids of the pest Nezara viridula (L). Laboratory experiments were conducted by allowing both parasitoid species to exploit an egg mass made of 10, 20, 30, or 40 hosts through single or simultaneous releases. Furthermore, under field conditions, egg masses consisting of 10 or 40 hosts were exposed in a tomato crop in order to validate laboratory investigation. RESULTS: The results show that the egg mass size is an important predictor of extrinsic competition in our study system as a higher proportion of T. basalis emerged from large egg masses, while O. telenomicida dominated in small egg masses. Analysis of reproductive traits of parasitoid species indicates that T. basalis has superior abilities in host exploitation compared with O. telenomicida. CONCLUSIONS: We found that contrasting reproductive traits of two competing egg parasitoid species facilitate coexistence on a shared stink bug host. This work also highlights the importance to consider extrinsic competitive interactions between parasitoid species in a biological control perspective. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Understanding competition between scelionid parasitoids that exploit the same host may provide insight into strategies that allow coexistence on a shared resource. Competition studies typically focus on interactions between native and exotic parasitoids that do not share an evolutionary history; however, coevolved parasitoids may be more likely to demonstrate strategies to avoid or exploit a shared resource. We examined intrinsic and extrinsic competition between Asian Trissolcus japonicus (Ashmead) and T. cultratus (Mayr) (Hymenoptera: Scelionidae) associated with Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) that share an evolutionary history. Interspecific interactions were assessed by providing parasitized egg masses to each species at various intervals post‐parasitism, and measuring host acceptance, developmental suitability, and guarding behaviour. Trissolcus japonicus showed high acceptance of parasitized hosts up to 72 h following oviposition by T. cultratus, despite a very poor developmental outcome. In contrast, T. cultratus generally avoided ovipositing in H. halys eggs containing T. japonicus early‐instar larvae but did not avoid parasitizing H. halys that contained eggs and third instar larvae. The adaptive value of this behaviour was supported by developmental outcome: T. cultratus outcompeted T. japonicus eggs but not early‐instar larvae, and a trophic shift occurred wherein T. cultratus developed as a facultative hyperparasitoid on third instar T. japonicus larvae. Trissolcus japonicus guarded egg masses 8–12× longer and displayed more aggressive interactions than T. cultratus, suggesting T. japonicus is the superior extrinsic competitor. Development as a facultative hyperparasitoid provided a competitive niche for Asian T. cultratus and confirms its instrinsic competitive superiority. This also occurs in a biologically distinct European population of T. cultratus, suggesting that facultative hyperparasitism as a competitive strategy is retained in geographically separated populations that have not coevolved with H. halys or T. japonicus. [ABSTRACT FROM AUTHOR]

The braconid wasp, Diachasmimorpha longicaudata (Ashmead), was introduced in Kenya from Hawaii for classical biological control of the invasive tephritid, Bactrocera dorsalis Hendel. Following reports that D. longicaudata had formed new associations with Ceratitis cosyra, laboratory experiments were conducted to assess the interaction between the introduced and the native parasitoid of C. cosyra; Psyttalia cosyrae (Wilkinson) under three scenarios: B. dorsalis only, C. cosyra only and mixed populations of the two species. Parasitoids were introduced to the host as sole, sequential and simultaneous releases. Host searching and probing events were five times higher for D. longicaudata than P. cosyrae with both hosts. Total parasitism was highest (78%) when D. longicaudata was released alone on C. cosyra, compared to 20% for P. cosyrae released on the same host. Releases of P. cosyrae on B. dorsalis resulted in 0% parasitism, compared to 64% parasitism by D. longicaudata. Specific parasitism for P. cosyrae was three times higher when P. cosyrae was released first in sequential releases on C. cosyra compared to when it was released after D. longicaudata. These findings suggest that the two parasitoids can both suppress C. cosyra but B. dorsalis acts as a reproductive sink for P. cosyrae. Our findings should form the basis of field investigations where options are much wider for both parasitoids.

Tephritidae fruit flies are parasitized by Braconidae wasps, of which some are used in biological control programs. Releases of exotic parasitoids might affect, or be affected by, native species exploiting a common host. We studied interspecific competition between the native African parasitoid Fopius caudatus (Szépligeti) and the exotic Asian parasitoid Fopius arisanus (Sonan) (both Hymenoptera: Braconidae) in African native Ceratitis cosyra Walker (Diptera: Tephritidae). Wasp behaviour on infested fruits and dissection of fruit fly eggs assessed acceptance, oviposition performance and suitability for egg development, parasitism, and effect of parasitism by heterospecific species. While F. arisanus outcompeted F. caudatus in parasitization of relatively younger eggs, chased away F. caudatus, and oviposited more, F. caudatus survived better than F. arisanus. Fopius caudatus parasitized more in 2-day-old C. cosyra eggs than in 1 or 3-day-old egg. More oviposition by F. caudatus was found in fruits previously exposed to F. arisanus , coinciding with presence of more developed host eggs, while such difference was not observed for F. arisanus. Fopius caudatus was an inferior competitor than F. arisanus in C. cosyra -infested African mango Irvingia gabonensis (Irvingiaceae). [ABSTRACT FROM AUTHOR]

[Display omitted] • Trissolcus japonicus and T. mitsukurii are valid potential biological control agents of H. halys. • Interspecific competition among BCAs can affect pest control success. • Multiparasitism caused a lower reproductive potential offspring production and wasted searching time. The invasive stink bug Halyomorpha halys , native to east Asia, is a severe agricultural pest of worldwide importance and biocontrol is a promising method for its long-term management. The two Asian egg parasitoids Trissolcus japonicus and Trissolcus mitsukurii are considered to be effective candidates as biological control agents. These species can co-occur in the same habitats and interspecific competition for hosts could therefore have an important role in natural control. We assessed the foraging behavior and the progeny production of both species under laboratory conditions with three different interspecific competition scenarios. With indirect competition, H. halys egg masses previously parasitized by the female of one species were offered to the competitor females after 0, 3, 5, or 7 days. With direct extrinsic competition, females of each species were tested in arenas either when introduced simultaneously (synchronous release) or when half of the host egg mass had already been parasitized by the other species (asynchronous release). Both Trissolcus species were able to parasitize host eggs already parasitized by the other species, although the progeny production always favored the species that arrived first on the host egg mass. However, in the synchronous releases scenario, T. mitsukurii displayed more aggressive behavior and spent more time defending the host egg mass than T. japonicus , resulting in a higher progeny production. Our results showed that multiparasitism among T. japonicus and T. mitsukurii , at least under laboratory conditions, resulted in a general waste of searching time, energy, eggs laid, and a lower reproductive potential by the second-arriving species on the host egg mass. [ABSTRACT FROM AUTHOR]

The competitive ability of the generalist parasitoid Meteorus pulchricornis was compared with that of the proposed new biological control agent Cotesia urabae to determine the impact the former species might have on the ability of the agent to control its host Uraba lugens Walker (Lepidoptera: Nolidae) in New Zealand. Behavioural observations were made of females of each species exposed together to groups of U. lugens larvae. Meteorus pulchricornis did not successfully attack U. lugens in the presence of C. urabae, and the mortality of the host in the presence of M. pulchricornis alone did not differ from mortality when no parasitoids were present. The presence of M. pulchricornis in the same arena did not reduce the impact of C. urabae on U. lugens compared to controls. Field collections of U. lugens larvae found limited evidence of larval parasitism by M. pulchricornis. These results suggest that the resident parasitoid M. pulchricornis is unlikely to interfere with the success of the proposed biological control agent C. urabae, should it be introduced to New Zealand. [ABSTRACT FROM AUTHOR]

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Simple Summary: Wasps, generally referred to as "farmers friends" because of their ability to control devastating fruit flies, were imported from Hawaii and released in Kenya for the management of the invasive Oriental fruit fly Bactrocera dorsalis. It was noted that the introduced wasp had developed a liking for the native fruit fly species Ceratitis cosyra which already has a native wasp controlling it. We therefore undertook a study to understand the interaction of the introduced and native wasp on the invader Oriental and native fruit flies. Our results show that when the native wasp attacks the invader fruit fly, the wasp is killed because of the strong immune system of the oriental fruit fly. The good news is that the introduced wasp efficiently controls both the invader and the native fruit flies. We have discussed these findings based on various scientific principles which favor the co-existence of the two wasps without any detrimental effect on their survival. We have also suggested that more studies be conducted in open field conditions where both fruit flies occur in abundance and choices regarding which fruit fly species to attack are much wider. The braconid wasp, Diachasmimorpha longicaudata (Ashmead), was introduced in Kenya from Hawaii for classical biological control of the invasive tephritid, Bactrocera dorsalis Hendel. Following reports that D. longicaudata had formed new associations with Ceratitis cosyra, laboratory experiments were conducted to assess the interaction between the introduced and the native parasitoid of C. cosyra; Psyttalia cosyrae (Wilkinson) under three scenarios: B. dorsalis only, C. cosyra only and mixed populations of the two species. Parasitoids were introduced to the host as sole, sequential and simultaneous releases. Host searching and probing events were five times higher for D. longicaudata than P. cosyrae with both hosts. Total parasitism was highest (78%) when D. longicaudata was released alone on C. cosyra, compared to 20% for P. cosyrae released on the same host. Releases of P. cosyrae on B. dorsalis resulted in 0% parasitism, compared to 64% parasitism by D. longicaudata. Specific parasitism for P. cosyrae was three times higher when P. cosyrae was released first in sequential releases on C. cosyra compared to when it was released after D. longicaudata. These findings suggest that the two parasitoids can both suppress C. cosyra but B. dorsalis acts as a reproductive sink for P. cosyrae. Our findings should form the basis of field investigations where options are much wider for both parasitoids. [ABSTRACT FROM AUTHOR]