The grasshoppers in question belong to the genus Trimerotropis, a speciose group of band-winged grasshoppers found throughout the American continent, from Canada down to Chile and Argentina, with their greatest abundance in desert and semi-desert regions. The genus currently comprises 49 recognized species, yet its members are notoriously difficult to tell apart morphologically. Diagnostic features include a pronotal crest always cut by two sulci, forewing bands crossing the dorsum in species that do not inhabit sandy terrain, relatively large eyes, hindwings usually marked with a clearly defined outer dark band, and a basal hindwing area that is yellow, yellow-green, or blue but never orange or red. Despite this ecological and taxonomic prominence, published records of parasitoids attacking Trimerotropis have been astonishingly scarce.

Until now, only a single confirmed parasitoid record existed for the entire genus: the flesh fly Blaesoxipha (Acridiophaga) caridei, reared from Trimerotropis ochraceipennis in Chile back in 1943. No parasitoid wasps have ever been documented in Trimerotropis species, although the grasshoppers do fall prey to sand wasps of the genus Tachysphex, which paralyze them as provisions for their nests. Some kleptoparasitic flies in the subfamily Miltogramminae have also been reported from paralyzed Trimerotropis individuals in sand wasp nests in the United States. Against this sparse backdrop, the new findings represent a significant expansion of knowledge.

The story began somewhat accidentally. Specimens of two Trimerotropis species were collected in 2023 as part of a research project investigating the evolutionary, environmental, and biotic mechanisms driving niche diversification in Oedipodinae grasshoppers, conducted by Dr. Tereza Jezkova’s team. Trimerotropis pallidipennis individuals were collected near the Mono Lake Navy Beach viewpoint in California on 16 August 2023, while T. melanoptera were gathered near the National Scouting Museum in New Mexico on 16 September 2023. The grasshoppers were captured with entomological nets and euthanized in the field with acetone-charged kill jars, since the project aimed to obtain material for genetic analyses.

What happened next transformed a routine collecting trip into a parasitological discovery. One femur from each grasshopper was removed and preserved in 100% ethanol for DNA work, and the remaining bodies were eviscerated through a small incision in the cervical membrane before being placed in newspaper envelopes lined with cotton. Approximately one week after fieldwork, when the specimens were being prepared for drying in an oven at 50 degrees Celsius, the researchers discovered fly puparia inside the entomological envelopes. Larvae had emerged from the grasshoppers after collection but before the drying process, and remarkably, they had survived despite their hosts having been submerged in acetone and subsequently eviscerated. The envelopes containing the puparia were then sealed in zip lock bags to allow adult fly development.

A single puparium was found among the T. pallidipennis specimens, from which an adult male fly successfully emerged. Two puparia were recovered from the T. melanoptera envelopes, though only one adult male emerged from those. The exact timing of larval emergence and adult fly development could not be determined because the puparia were found in envelopes, with separate envelopes used for each grasshopper species. The adult flies were preserved in 70% ethanol and sent to the Laboratório de Diptera of the Museu de Zoologia da Universidade de São Paulo in Brazil for identification, where specialists dissected the male terminalia in potassium hydroxide solution and compared the specimens against the holotype male of Sarcophaga angustifrons Aldrich, 1916, held at the National Museum of Natural History in Washington, DC.

The identification confirmed the flies as Blaesoxipha (Acridiophaga) angustifrons, a Nearctic species widely distributed from the southern United States to Canada. The genus Blaesoxipha, which comprises more than 240 species in 10 subgenera worldwide, is characterized by a posteromedian row of spines on the trochanter of the hind leg in both sexes, along with distinctive male terminalia features including a cercus bent posteriorly with short erect spines on its distal dorsal surface. Species in the subgenus Acridiophaga are distinguished by a setose proepisternum and male terminalia with the apical part of the juxtal lobes curving laterally or outwards. Externally, B. angustifrons closely resembles B. caridei, and the two were even considered synonymous in earlier works, but they can be separated by the length of the median stylus in the male terminalia, which is completely covered by the juxtal lobe in lateral view in B. angustifrons.

The host records themselves are scientifically valuable. Trimerotropis pallidipennis is the most widely distributed Oedipodinae grasshopper in the New World, ranging from southwestern Canada to at least central Argentina, and inhabits dry grasslands including western prairies, desert grasslands, and desert scrub. Trimerotropis melanoptera, recognizable by a very broad black band on the hindwings, a reddish abdomen, and a single pale band on the inner face of the hind femora, occupies open grasslands and desert grasslands. Beyond these two new hosts, confirmed host records for B. angustifrons are scarce and sometimes unclear. The Nearctic grasshopper Conozoa carinata was reported as a host by Pape in 1994, though without a specified locality. Other published associations, including probable parasitism of several Melanoplus species and Camnula pellucida in Canada, rest on questionable or unpublished data and remain pending revision.

The biology of these parasitoid flies is as striking as their taxonomy. Blaesoxipha females rely on visual cues when hunting, darting at flying or jumping grasshoppers or stalking them on the ground. They typically deposit a single, well-developed first-instar larva on or in the host, either on the ventral wing surface or injected between the abdominal intersegmental membranes. These flies have been recorded from many grasshopper groups and are considered important agents for biological control of pest grasshoppers. Yet attempts to use other sarcophagid parasitoids against Nearctic grasshoppers have met with mixed success; tests involving four Palaearctic species on numerous North American grasshoppers, including Spharagemon campestris, formerly classified as Trimerotropis, proved unsuccessful.

The practical stakes of this gap in knowledge are considerable. Some Trimerotropis species, including T. pallidipennis, can significantly impact crops during outbreaks by feeding on a wide variety of plants. Understanding which natural enemies attack these grasshoppers, and under what circumstances, could prove essential for managing outbreaks and appreciating the ecological checks that keep grasshopper populations in balance. The new records from California and New Mexico significantly expand the known host range of B. angustifrons and contribute to the limited understanding of host-parasitoid dynamics in this ecologically important genus. They also serve as a reminder that even routine fieldwork, conducted for entirely different purposes such as population genetics, can yield unexpected discoveries when researchers pay close attention to what emerges from their collecting envelopes.

Subject of Research: Parasitoid flesh fly host associations with Nearctic Trimerotropis grasshoppers

Article Title: New records of parasitoid flies ( Diptera , Sarcophagidae ) in Nearctic species of Trimerotropis Stål ( Orthoptera , Acrididae , Oedipodinae , Trimerotropini )

Article References: Gudin, F. M., Martins Silva, D. S., Otto, A., Bracken, J., & Jeskova, T. (2026). New records of parasitoid flies (Diptera, Sarcophagidae) in Nearctic species of Trimerotropis Stål (Orthoptera, Acrididae, Oedipodinae, Trimerotropini). Journal of Orthoptera Research, 35(1), 197-202. https://doi.org/10.3897/jor.35.175567

Image Credits: AI Generated

DOI: 10.3897/jor.35.175567

Keywords: Trimerotropis, Blaesoxipha, Sarcophagidae, parasitoid, grasshoppers, Acrididae, Oedipodinae, host-parasitoid, New Mexico, California, biological control, entomology