Biology of the Armored ScaleRhizaspidiotus donacis(Hemiptera: Diaspididae), a Candidate Agent for Biological Control of Giant Reed

The development, survival, and reproductive output of the armored scale Rhizaspidiotus donacis Leonardi (Hemiptera: Diaspididae) were determined as part of an evaluation of this scale for biological control of giant reed, Arundo donax L. Scale crawlers produced by females collected in southern France and Spain lived for less than two d in the absence of a host. On A. donax shoots held under a diurnally variable temperature regime (15–26°C), crawlers settled on leaf collars and axillary stem bases and completed the first instar within 14 d. Winged adult males emerged within six wk and lived 1.7 d in vials. Immobile adult females were observed 75 d after crawler release. Development time to adult was reduced 15% in males and 28% in females when scales were reared at a constant temperature of 26°C. Survival from crawler to adult was 20–25%. The generation time for laboratoryreared females was 170d and their average life span was 203 d. Females from field collections produced an average of 85 live crawlers, 2.7-fold more than did colony-reared females. Across 31 field collections, female size was correlated to the percentage of scales that were reproductive. However, among eight collections from two Spanish sites, size varied but was not correlated to reproductive success. Peak reproduction from field collections occurred between November and March, and the scale completed two generations per year. Biological information about R. donacis will aid production, release, and field evaluation of this scale for biological control of invasive A. donax in North America.