Increase in gall fly biocontrol agents
quadrifasciata larvae are eaten by Metzneria and Larinus larvae. Studies in Canada have shown that a combination of both Urophora flies and the root borer Sphenoptera jugoslavica can reduce diffuse knapweed seed production by 98 percent. quadrifasciata have reduced seed production by up to 95 percent in spotted knapweed. affinis, Metzneria paucipunctella, and Larinus minutus, and other seed head feeding agents. quadrifasciata has been found to compliment the biological control activities of U. quadrifasciata will increase as knapweed densities decline because it is less dependent on dense populations of knapweed than U. This is the most widely distributed knapweed biocontrol agent. Urophora quadrifasciata entered the US in 1980. quadrifasciata attack, but the combination of both fly species enhances seed reduction. affinis in the seedhead tends to discourage U. There does not appear to be a decrease in the number of seedheads on plants attacked by U. quadrifasciata are destroyed and adjacent florets abort (approximately two seeds destroyed for each U. Otherwise, first generation overwinters in head.įlorets damaged by U. Emerging second generation adults (August) attack later forming seedheads and emerge the following spring with the onset of knapweed seedhead buds.
First generation flies pupate 20 to 25 days after oviposition, about the time that seed development is complete. Larvae consume most of the gall tissue during their development. Larval feeding induces plants to form a thin papery gall around the larvae (unlike the hard gall surrounding U. Larvae will only develop in pollinated seedheads. Eggs hatch in 3 to 4 days and larvae bore down a floret to an ovary. Eggs are laid singly among developing florets and a seedhead may be attacked several times. Flies preferentially attack seedheads that measure 0.22 to 0.38 inch (5 to 8 mm) long with distinct seed embryos. Urophora quadrifasciata has at least one generation per year with a certain percentage emerging for a non-obligatory second generation. Pupae are brown, and 0.12 inch (3 mm) long. affinis, larval feeding causes plants to form a thin, papery gall, which surrounds the larva and is the same color as the florets. A dark brown, elliptical anal plate develops by the end of the feeding period (the anal plate of U. Late instar larvae are creamy-white, barrel-shaped, with heads that are slightly retracted into the thorax. Larvae go through three larval stages, or instars. Eggs are white when deposited, elongate and crescent shaped. 22), making this fly very easy to distinguish from U.
#INCREASE IN GALL FLY BIOCONTROL AGENTS TRIAL#
A greenhouse trial using both agents had predicted. This work reports the first post-release evaluation of the effect of both agents acting together in the field. Eupatorium adenophorum) (Asteraceae), in South Africa. quadrifasciata flies are approximately 0.16 inch (4 mm) long, black, with black, UV pattern on the wings (Fig. Two biocontrol agents, a leaf-spot pathogen, Passalora ageratinae, and a stem gall fly, Procecidochares utilis, have been released against Crofton weed, Ageratina adenophora (syn.
Spotted, diffuse, squarrose, meadow, black, and brown knapweedsĪdult U.