Agapeta zoegana
Attacks: Diffuse knapweed, Meadow knapweed, Spotted knapweed
Agent Type: Root feeding moth
Origin: Populations released in BC orginated in Europe.
Adult: Agapeta zoegana on knapweed Adult moths are bright yellow and black, 1-2 cm long with a wingspan of 1.5-2.3 cm. Forewings are bright yellow with brown-black markings; hindwings are dark grey. Females have a larger and more rounded abdomen than males. The males have a pair of clasping pincers at the end of their abdomen. Adults emerge from roots during mid-June to mid-August and begin to mate and lay eggs within 24 hours. Females oviposit 66 - 185 eggs onto leaves or stems close to the crown, selecting plants with a root diameter of 2.4 mm or larger. Temperatures between 18-30°C are best for mating. Cool, windy days will delay oviposition. Adults live 10 to 14 days.
Egg: The flattened, oval shaped eggs measuring 0.75mm x 0.45mm, are initially white and turn yellow-red after four days. With magnification, a network of meshed lines can be seen on the outer surface. Eggs hatch in seven to ten days.
Larva/Pupa: Larvae are segmented, with white bodies and brown heads. Newly hatched larvae move to the root crown to begin feeding. The larvae develop through six instars. The first through fourth instars mine about 10 cm of the taproot over 40-45 days. They produce a whitish web tunnel that encloses around the larvae as they create a spiral trail downward before returning to the top of the root. They can move through the soil to adjacent roots within 10 cm. They mature ind 70 days. Pupation takes about eight weeks which occurs the following spring within the webbing. Multiple larvae can exist on a single root.
Overwintering: It will overwinter in any larvae instar within the root.
Location & Efficacy: Agapeta zoegana larvae feed on the outer root layers, creating spiral tunnels which can kill small plants and prevent the flowering of larger ones. While entering, they often damage the vegetative stem bud, causing the plant to send up multiple short stems instead of a single bolt. Plants may become susceptible to secondary insect or pathogen attack.
Habitat: A. zoegana is common to the mesic, cooler areas where knapweed grows, and is often associated with moderate humidity and temperatures within the Bunchgrass and Ponderosa pine biogeoclimatic zones. It can tolerate cold winters, but requires a long growing season. Sites over 1000m may not allow sufficient time for development. Suitable host plants have 2.4mm diameter roots growing in undisturbed locations that are not mowed, grazed or cultivated.
Its native distribution includes the former Yugoslavia, eastern Rumania, western Hungary and eastern Austria. Small populations occur in the Upper Rhine Valley, but it is absent in the Swiss Valais.
In BC, releases have occurred in the Bunchgrass, Coastal Douglas-fir, Coastal western hemlock, Interior cedar-hemlock, Interior Douglas-fir, Montane spruce, Ponderosa pine and Sub-boreal spruce biogeoclimatic zones. Establishment and dispersal has been found throughout each of these with the exception of the Montane spruce and Sub-boreal spruce zones.
BC History: The first A. zoegana release was made in 1982. Since then, many thousands of adult moths have been collected and redistributed throughout the province.
Field Results: The species is well dispersed in the Southern Interior, and can be seen from mid-June through mid-August. Recently, observations indicate that, as A. zoegana disperses its density declines. Many larvae can be found on a single root, for example, 56 larvae were found on a large root (over 20 cm long). 28 Cyphocleonus achates larvae were also present on the same root.
Handling/ Collecting: Using light suction, adults can be aspirated head first into collection containers. Peak periods are in early mornings or evenings. Adults rest low on the plants or on the soil surface during the day. Disturbing the plants will cause the adults to take short flights.
Notes: A. zoegana can exist with other root feeding biocontrol agents, including Sphenopterajugoslavica and Cyphocleonus achates.
Field Guide: Operational Field Guide - Agapeta zoegana