Seasonal incidence of Stenodiplosis sorghicola (Coquillett) (Diptera: Cecidomyiidae) and its parasitoids on Sorghum halepense (L.) Pers. in south‐eastern Queensland, Australia

Abstract

To quantify the role of Johnson grass, Sorghum halepense, in the population dynamics of the sorghum midge, Stenodiplosis sorghicola, patterns of flowering of Johnson grass and infestation by sorghum midge were studied in two different climatic environments in the Lockyer Valley and on the Darling Downs in south-eastern Queensland for 3 years. Parasitism levels of S. sorghicola were also recorded. In the Lockyer Valley, Johnson grass panicles were produced throughout the year but on the Darling Downs none were produced between June and September. In both areas, most panicle production occurred between November and March and infestation by S. sorghicola was the greatest during this period. The parasitism levels were between 20% and 50%. After emergence from winter diapause, one to two generations of S. sorghicola developed on S. halepense before commercial grain sorghum crops were available for infestation. Parasitoids recorded were: Aprostocetus diplosidis, Eupelmus australiensis and two species of Tetrastichus. Relationships between sorghum midge population growth rate and various environmental and population variables were investigated. Population size had a significant negative effect (P < 0.0001) on population growth rate. Mortality due to parasitism showed a significant positive density response (P < 0.0001). Temperature, rainfall, open pan evaporation, degree-days and host availability showed no significant effect on population growth rate. Given the phenology of sorghum production in south-eastern Queensland, Johnson grass provides an important bridging host, sustaining one to two generations of sorghum midge. Critical studies relating population change and build-up in sorghum to sorghum midge populations in Johnson grass are yet to be performed.

A new species of Stenodiplosis (Diptera: Cecidomyiidae) on florets of the invasive common reed (Phragmites australis) and its effects on seed production

“…Another midge in the genus Stenodiplosis (S. sorghicola) is an important pest of the agriculturally valuable plant sorghum (S. bicolor), that is grown globally (Nwanze et al 1998;Franzmann et al 2006;Lloyd et al 2007;Damte et al 2009). The sorghum midge is parasitised by members of the wasp genus Aprostocetus (Nwanze et al 1998;Lloyd et al 2007). Stenodiplosis sorghicola also attacks the related, but noncrop plant Sorghum halepense (Johnson grass), where it is also host to members of the genus Aprostocetus (Lloyd et al 2007).…”

“…The sorghum midge is parasitised by members of the wasp genus Aprostocetus (Nwanze et al 1998;Lloyd et al 2007). Stenodiplosis sorghicola also attacks the related, but noncrop plant Sorghum halepense (Johnson grass), where it is also host to members of the genus Aprostocetus (Lloyd et al 2007). In that system, the midge exhibits negative densitydependent growth, which appears to be at least partly due to a density-dependent increase in mortality by parasitoids (Lloyd et al 2007).…”

“…Stenodiplosis sorghicola also attacks the related, but noncrop plant Sorghum halepense (Johnson grass), where it is also host to members of the genus Aprostocetus (Lloyd et al 2007). In that system, the midge exhibits negative densitydependent growth, which appears to be at least partly due to a density-dependent increase in mortality by parasitoids (Lloyd et al 2007). Results such as these suggest that the efficacy of S. phragmicola as a potential control agent for P. australis could be influenced by Aprostocetus spp., and particularly that the wasp might reduce the maximum size of S. phragmicola populations.…”

“…1998; Lloyd et al . 2007). Stenodiplosis sorghicola also attacks the related, but noncrop plant Sorghum halepense (Johnson grass), where it is also host to members of the genus Aprostocetus (Lloyd et al .…”

“…This value (and our average value of ∼10%) is substantially higher than estimates of infestation rates for S. sorghicola on the related Johnson grass ( S. halapense ), where fewer than 5% of spikelets were found to be infested (Lloyd et al . 2007).…”