Parasitism of Spissistilus festinus (Hemiptera: Membracidae) by Halictophagus jordani (Strepsiptera: Halictophagidae) in Arizona alfalfa fields

Authors: Hepler, James; Ohler, Bonnie; SCHUTZE, INANA - Oak Ridge Institute For Science And Education (ORISE); Hull, Jimmy; Cooper, William

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2026
Publication Date: 6/13/2026
Citation: Hepler, J.R., Ohler, B.J., Schutze, I.X., Hull, J.J., Cooper, W.R. 2026. Parasitism of Spissistilus festinus (Hemiptera: Membracidae) by Halictophagus jordani (Strepsiptera: Halictophagidae) in Arizona alfalfa fields. Journal of Insect Science. 26(3). https://doi.org/10.1093/jisesa/ieag046.
DOI: https://doi.org/10.1093/jisesa/ieag046

Interpretive Summary: Three-cornered alfalfa hoppers, Spissistilus festinus, are pests of alfalfa, soybean, and peanut throughout much of the United States. Recently, they have been shown to be vectors of Grapevine Red Blotch Disease, a major threat to grape production in California and elsewhere. Identifying natural enemies of this pest is therefore a matter of interest to US agriculture. Alfalfa hoppers collected from Arizona alfalfa fields were unexpectedly parasitized on a large scale by an unidentified Strepsiptera. The hopper population was intensively sampled to determine the scale of parasitoid attack, and the parasitoid was identified as Halictophagus jordani. The parasitoid, previously known only from eastern Texas and Louisiana, was found parasitizing 45% of the nearly 4000 hoppers sampled. Based on the biology of other related parasitoids, H. jordani may be an important factor in the regulation of alfalfa hopper populations by rendering infected individuals sterile. Study findings are significant because they report widespread parasitism by H. jordani 1500 km (over 900 miles) west of previously reported populations. This suggests that this parasitoid may be present in other areas of the USA where the alfalfa hopper is an emerging problem, potentially enabling biological control efforts to be developed.

Technical Abstract: Sweep net samples taken from alfalfa fields in Arizona contained three-cornered alfalfa hopper, Spissistilus festinus, abundantly stylopized by an unknown strepsipteran parasitoid. Targeted sampling of S. festinus was conducted over a two-week period from Oct-Nov to determine the rate of parasitism and identify the parasitoid. Adult male parasitoids were reared for morphological identification. Additionally, representative male, female, and larval parasitoids were identified through COI barcoding gene sequencing. Strepsiptera were determined to be Halictophagus jordani, previously reported only from eastern Texas and Louisiana, USA. All S. festinus adults and mature H. jordani were sexed and counted, and all apparently unstylopized hoppers were dissected to look for internal parasitoid larvae. Parasitism rates, parasitoid loads, and parasitoid sex ratios of both host sexes were compared. Overall, 3791 S. festinus were examined. 1092 (28.8%) bore mature H. jordani protruding between abdominal segments. A further 613 (16.2%) were found to contain internal larvae upon dissection, yielding a total stylopization rate of 45.0%. Male and female hoppers did not differ significantly in mature male, female, or total parasitoid load, though female hoppers were significantly more likely to be parasitized than male hoppers. Parasitoid infrapopulations showed evidence of segregation by parasitoid sex, but no relationship was detected between infrapopulation sex ratio and host sex. The size of an infrapopulation strongly predicted its sex ratio, which became more male-skewed with increasing size. These findings indicate that H. jordani is more widely distributed than previously believed and suggest its potential role in the biological control of S. festinus.