Life History of the Ambrosia Beetle Xylosandrus germanus (Coleoptera: Scolytidae)1

The field life history of Xylosandrus germanus (Blandford) was studied in North Carolina, Ohio, Tennessee, and Illinois, particularly as associated with black walnut ( Juglans nigra L.), and the number of instars was determined. The beetle was also reared in the laboratory on artificial diet. Galleries are excavated by the females and are composed of entrance tunnels, brood chambers where eggs are laid and larval development begins, and one to three branch tunnels where development continues. The species is bivoltine and overwinters as adults, primarily females, in galleries of its host plants. The number of progeny per gallery averaged 16.5; the sex ratio was 10 females to 1 male. Flight activity began in late March to early April and continued until late August and early September. Average seasonal flying heights of adult females ranged from 1.2 to 1.6 m. On artificial diets in the laboratory, X. germanus laid an average of 1 egg per day and an average of 18.0 eggs per female. Development time from egg to adult was 24.9 days at 24°C. X. germanus has three instars. Behavior during mating, and brood production and rearing, is discussed.