Hugo A. Cordo

Biology of Apagomerella versicolor (Boheman) (Coleoptera: Cerambycidae) in Argentina, a candidate for biological control of cocklebur (Xanthium spp.)

The biology of the cerambycid beetle, Apagomerella versicolor (Boheman), a candidate for biocontrol of cocklebur, Xanthium strumarium L., in the US, was studied in Argentina where it attacks X.strumarium cavanillesii Love and Dansereau. A.versicolor is univoltine and adults appear in the field in early spring. In the laboratory, the adults lived an average of 18.5 days. Each female laid an average of 38 eggs, one egg per oviposition. The incubation period for the eggs lasted 10 days at 25C and 80% RH. The larval stage had seven instars. Eggs were laid in the stems and larvae fed boring their way toward the root. At the beginning of fall, larvae girdled the stem of the mature plant near the crown, causing the dried aerial part of the plant to fall over. The last instar entered diapause and pupated within the roots in dead and dry plants until spring. Exposure of larvae to temperatures lower than 12C for at least 8 days ended diapause. All larvae survived continuous exposure to � 8C for 3 days, and immersion of larvae in tap water for 20 days did not affect their survival. In Buenos Aires, Argentina, three parasitoids were found attacking the larvae; a braconid, Nealiolus n. sp., parasitized 61.5% of the larvae in 1988. Attack by A.versicolor reduced fruit production in X.s.cavanillesii by 66%, and killed young plants. A.versicolor has some attributes of a biocontrol agent of Xanthium spp. These attributes, along with cold tolerance, immersion tolerance, broad habitat distribution from tropical forest to desert, suggest that it would be an effective biocontrol agent of Xanthium spp. Published by Elsevier Science (USA).