Tuesday, May 12, 2015

Sugarcane Aphids in North Texas

   Surveys of Johnsongrass this spring indicate the sugarcane aphid SCA may have overwintered this year in north central Texas.  This is contrary to the earlier assumption that SCA could not overwinter in regions where its host plants, Johnsongrass and sorghum, did not remain green.  Thus, it was thought that SCA infestations in this region resulted from winged aphids carried by the wind from south Texas. While winged migrants from the south may still be important in initiating infestations in north central Texas, there is now the possibility that overwintering (local) SCA may also play a role. A likely scenario is that SCA numbers in Johnsongrass will eventually increase this spring to numbers that generate winged forms which can then fly or be blown from Johnsongrass into nearby sorghum fields. 

This spring, SCA have been found in Johnsongrass as follows: 
April 9, Hill County, near Hillsboro, TX,   
April 14, McLennan County, near McGregor, TX,   
May 5,  Hunt County, near Greenville, TX,   
May 5, Fannin County,  near Bonham, TX  

     Numbers vary from 2-3 aphids to up to 30 per colony, and are more abundant at the southern site (McLennan County).  In the most northern site, Fannin County which is on the Oklahoma border, SCA were found on only 2 of 100 Johnsongrass stems examined. Thanks to Marty Jungman who helped with the survey in Hill County. 
    I assume these are overwintering SCA since it is too early in the spring to expect winged migrants from the south to have initiated these colonies and, except for one individual in a colony of 30, winged SCA aphids have not been observed at any of these sites. In addition to SCA, bird-cherry oat aphids, greenbugs, corn leaf aphids and yellow sugarcane aphids (the latter the most abundant), along with a very few aphid  mummies, were observed in these samples.