Effect of precipitation and temperature on larval survival of Cephus cinctus (Hymenoptera: Cephidae) in barley cultivars

Authors: ACHHAMI, BUDDHI - Montana State University; Reddy, Gadi V.P.; SHERMAN, JAMIE - Montana State University; PETERSON, ROBERT - Montana State University; WEAVER, DAVID - Montana State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2020
Publication Date: 5/19/2020
Citation: Achhami, B.B., Reddy, G.V., Sherman, J.D., Peterson, R.K., Weaver, D.K. 2020. Effect of precipitation and temperature on larval survival of Cephus cinctus (Hymenoptera: Cephidae) in barley cultivars. Journal of Economic Entomology. 113(4):1982-1989. https://doi.org/10.1093/jee/toaa097.
DOI: https://doi.org/10.1093/jee/toaa097

Interpretive Summary: Wheat stem sawfly (WSS) is serious and problematic pest on wheat in North America. This species is not only widening its geographical range to eastern Colorado and northwestern Kansas, but also adapting to the relatively recent host, barley, which was traditionally recommended as a rotational crop in wheat production to control WSS outbreak. It was reported that WSS infestation and larval survival is increasing in barley grown in Montana. Our previous research indicated that host plant resistance is a key factor to consider for increasing larval mortality in barley cultivars. However, it has been found that the expression of host plant resistance traits is often governed by temperature and precipitation during the growing season. Thus, we assessed larval survival rates from early growth to the beginning of autumnal diapause in eight barley cultivars. We found that crop growing degree days was a better predictor of larval survival rates than growing season temperature and precipitation in barley cultivars. These findings bolster WSS management options by better characterizing plant defenses that decrease larval survival.

Technical Abstract: Host plant traits strongly affect survivorship of insect herbivores, and host suitability is especially important for the wheat stem sawfly (WSS), Cephus cinctus Norton (Hymenoptera: Cephidae), which spends its entire egg, larval, and pupal periods in a single stem. Measuring larval survival inside stems from egg hatch through diapause-mediated dormancy is a potential measure of population size for the next year but is also useful in assessing effects of growing season precipitation and temperature. Larval growth is synchronized with host plant growth, and the larvae cannot switch hosts. Thus, incorporating plant physiological time, as growing degree days, may be a better predictor of larval survival. Therefore, we assessed WSS survival from early larval growth to the beginning of autumnal diapause in barley cultivars selected from across feed, forage, and two- or six-row malt groups. Field experiments were conducted in Gallatin and Chouteau counties, Montana in 2016 and 2017. We used Kaplan-Meier estimation to assess larval survival among cultivars. We found that the survival of pre-diapause larvae was greatest in ‘Hockett’ (36.5%) and lowest in ‘Celebration’ (15.4%). Precipitation and temperature during the growing season affected temporal patterns for larval survival across study sites. Adjusting survivorship curves using site-specific growing degree day accumulation allowed cultivar-specific survivorship to be estimated more precisely for each site, despite differing environmental influences. Our findings suggest that measuring WSS survival across barley cultivars and standardizing by site-specific growing degree days may provide better recommendations on barley cultivars that impede WSS population growth and reduce economic losses.