Oecanthus nigricornis(Orthoptera: Gryllidae) as the first known host ofStylogaster neglecta(Diptera: Conopidae)

Abstract

The conopid fly Stylogaster neglecta Williston (Diptera: Conopidae) is a parasitoid with no known host. We report this species as the first recorded dipteran parasitoid of Oecanthus nigricornis Walker (Orthoptera: Gryllidae) (black-horned tree crickets). We reared field-collected O. nigricornis juveniles over several months in 2017 and found that larval S. neglecta emerged from them during late July into August. We estimated the incubation period for S. neglecta larvae to be around 30 days based on the length of time it took for them to emerge from the host and pupate (subsequently all hosts died). We documented several cases of multiple parasitism. In 2018, we dissected O. nigricornis sampled from four sites across southern Ontario, Canada and upstate New York, United States of America and found that the percentage of juvenile O. nigricornis parasitised ranged 2–39%. Further sampling will be necessary to determine whether this variation represents consistent population differences or between-year variation in parasitism.

Sex differences in survival: viability selection in nymphal tree crickets from a conopid fly parasitoid

“…First, our finding of a sex difference (no significant effects of parasitism on female body size) are difficult to explain with differential growth. In addition, in order to reduce the effect of any differential growth between parasitised and non-parasitised crickets we sampled at the beginning of the season when S. neglecta parasitises hosts (Etzler et al 2020). To control for effects of internal parasitoid feeding on host size, our main analysis used only hosts with unhatched eggs.…”

“…Sampling took place between July 11th and July 31th 2018 (Table 1). Etzler et al (2020) found that tree crickets were only parasitised in a short time window from mid-July until early August, and the timing of our sampling was intended to collect crickets at the beginning of this period. At this point, crickets would be likely to be parasitised but not yet had time to moult, and so their body size would likely be unchanged from when they were parasitised.…”

“…To reduce possible effects of S. neglecta larval hatching and growth on nymphal cricket body size, data on crickets with larvae were removed for the main (eggs-only) analysis. Only crickets in their third to fifth instar were sampled, as these are the main host stages (Etzler et al, 2020). Crickets were immediately frozen and preserved in 70% ethanol.…”

“…Here we investigate viability selection caused by this fly parasitoid. We examine selection on both size and sex because sex differences in developing nymphal traits affecting the fitness of adult tree crickets, such as size, (Brown, 1999(Brown, , 2008, may well expose male and female nymphs to different risk of fly attack (Etzler et al, 2020).…”

“…Isodontia mexicana wasps target adult tree crickets, but recently a high proportion of cricket nymphs in the same study population were shown to fall victim to a parasitoid fly Stylogaster neglecta Williston. (Diptera: Conopidae) (Etzler et al ., 2020). Here we investigate viability selection caused by this fly parasitoid.…”