|Cordo H A,|
|Deloach Jr, Culver|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 3, 1994
Publication Date: N/A
Interpretive Summary: Snakeweeds are among the most serious weeds of western rangelands where they reduce production of forage and they poison livestock. Their unpredictable variation in abundance and the low productivity of these semi-arid areas make herbicidal and mechanical controls expensive and economically risky. We have found several insects in Argentina that attack ksimilar but different snakeweed species, and these insects appear to be good candidates for biological control. In Argentina, we conducted detailed studies of the life cycle, reproduction, mating behavior, the method by which larvae enter the plant, and response to temperature of one of these insects, a clear-winged moth whose larvae feed in the roots of snakeweeds. Field studies indicated that the larvae damage snakeweeds throughout the year, that they are not heavily parasitized, and that they occur in several semi-arid climatic zones. These characteristics indicate that the species could become an effective control agent for snakeweeds if introduced into North America.
Technical Abstract: Adult Carmenta haematica are day-flying moths with orange (female) or clear (male) wings and a wingspan of 20 to 24 mm. Adults mated in bright sunlight. Females lived an average 2.3 days and laid an average 240 eggs each on stems and twigs of the host plant. Only 66% of the eggs hatched mostly in the 4 h before dawn. Larvae had seven instars and reached ca. 24 mm long when full grown. Larvae entered the plant at the base of twigs or leaves or sometimes directly into the crowns. They were cannibalistic after the second instar, and usually only one large larva occurred in a plant in the field. Larger larvae tunneled in the larger roots, and made an exit hole in a large stem 5-8 cm above the crown where they pupated; a silken tube often protruded from the exit hole. The life cycle required ca. 136.5 days at 30 deg C: 12 days for the egg, 107 for the larva, 16.5 for the pupa and 1 day for the adult to reach peak oviposition. Larval survival decreased below 0 deg C, and all died after 1 day at -15 deg C. Larvae pupated in mid-summer, adults emerged in late summer, and larvae developed during the fall, winter and spring. The species was mostly univoltine, but the presence of some large larvae and pupae during most months indicated some variation. In the field, larvae infested 20 to 25% of medium-sized or large plants. At three locations, the combined attack by C. haematica and other root borers killed most plants of Gutierrezia solbrigii Cabrera and Grindelia chiloensis Cabrera