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Abstract Mating signals of insects do not only attract their intended receivers but also eavesdropping parasites and/or predators. As a result, an arms race between the host or prey and the eavesdropper ensues, propelling their co‐evolution and potentially contributing to their diversification. Here, we investigate the species interaction of the flyOrmia lineifronsthat usesNeoconocephaluskatydids as hosts for its lethal larvae. We surveyed the host use ofO. lineifronsover a 2‐year period in Kentucky and determined which species were used as hosts, the parasitism rate of each katydid host, and how many generations per year the fly displays. Four of the six surveyedNeoconocephalusspecies were parasitized and killed (Neoconocephalus triops,Neoconocephalus velox,Neoconocephalus robustus,Neoconocephalus nebrascensis) byO. lineifrons. Three of these katydid species were previously not known to be hosts ofO. lineifrons. Two of the six species were not parasitized in either year (Neoconocephalus bivocatus,Neoconocephalus retusus) even thoughO. lineifronswas active when they called. The parasitism rate of each host peaked between 38% and 100% across years. The fly had three distinct generations per year, and each generation used different katydid species as hosts. We discuss the importance of the synchronization of the three fly generations with their hosts as well as potential counteradaptations of the hosts. These semi‐independent arms races could provide valuable insights in the diversification of the hosts and their parasitoid. 

The ability to respond to environmental changes plays a crucial role for coping with environmental stressors related to climate change. Substantial changes in environmental conditions can overcome developmental homeostasis, exposing cryptic genetic variation. The katydidNeoconocephalus triopsis a tropical species that extended its range to the more seasonal environment of North America where it has two reproductive generations per year. The harsher winter conditions required adults to diapause which resulted in substantially different mating calls of the diapausing winter animals compared to the non-overwintering summer animals in northern Florida. The summer call corresponds to that of tropical populations, whereas the winter call represents the alternative call phenotype. We quantified call plasticity in a tropical (Puerto Rico) and a temperate population ofN. triops(Florida) that differ in experiencing winter conditions in their geographic regions. We hypothesized that the plastic call traits, i.e., double-pulse rate and call structure, are regulated independently. Further, we hypothesized that phenotypic plasticity of double-pulse rate results in quantitative changes, whereas that of call structure in qualitative changes. We varied the photoperiod and duration of diapause during male juvenile and adult development during rearing and analyzed the double-pulse rate and call structure of the animals. Double-pulse rate changed in a quantitative fashion in both populations and significant changes appeared at different developmental points, i.e., the double-pulse rate slowed down during juvenile development in Florida, whereas during adult diapause in Puerto Rico. In the Florida population, both the number of males producing and the proportion of total call time covered by the alternative call structure (= continuous calls) increased with duration spent in diapause. In the Puerto Rico population, expression of the alternative call structure was extremely rare. Our results suggest that the expression of both pulse rate and call structure was quantitative and not categorical. Our systematic variation of environmental variables demonstrated a wide range of phenotypic variation that can be induced during development. Our study highlights the evolutionary potential of hidden genetic variation and phenotypic plasticity when confronted with rapidly changing environments and their potential role in providing variation necessary for communication systems to evolve. 

Antagonistic species relationships such as parasitoid/host interactions lead to evolutionary arms races between species. Many parasitoids use more than one host species, requiring the parasitoid to adapt to multiple hosts, sometimes being the leader or the follower in the evolutionary back-and-forth between species. Thus, multi-species interactions are dynamic and show temporary evolutionary outcomes at a given point in time. We investigated the interactions of the multivoltine parasitoid fly Ormia lineifrons that uses different katydid hosts for each of its fly generations sequentially over time. We hypothesized that this fly is adapted to utilizing all hosts equally well for the population to persist. We quantified and compared the fly’s development in each of the four Neoconocephalus hosts. Cumulative parasitism rates ranged between ~14% and 73%, but parasitoid load and development time did not differ across host species. Yet, pupal size was lowest for flies using N. velox as a host compared to N. triops and other host species. Successful development from pupa to adult fly differed across host species, with flies emerging from N. triops displaying a significantly lower development success rate than those emerging from N. velox and the other two hosts. Interestingly, N. triops and N. velox did not differ in size and were smaller than N. robustus and N. nebrascensis hosts. Thus, O. lineifrons utilized all hosts but displayed especially low ability to develop in N. triops, potentially due to differences in the nutritional status of the host. In the multi-species interactions between the fly and its hosts, the poor use of N. triops may currently affect the fly’s evolution the most. Similarities and differences across host utilization and their evolutionary background are discussed.