Three effective, complementary biological control agents could contribute to a long term solution to the control of Paterson’s Curse in Tasmania, Paterson’s Curse Crown Weevil, (Mogulones larvatus) Paterson’s Curse Taproot Flea Beetle, (Longitarsus echii), and Pollen Beetle (Meligethes planiusculus) as part of an integrated management program.
Paterson’s Curse Crown Weevil (Mogulones larvatus)
The Paterson’s Curse Crown Weevil was released and established in the Tamar in the St Leonards area in 2008.
This agent has one generation each year. Adults emerge in spring to early summer and feed on flowering Paterson’s Curse before aestivating (torpor) over summer. Adults become active again in autumn stimulated by rain to feed on rosette leaves and lay eggs on the petioles and leaf blades.
Eggs can be laid over a long period from autumn to the end of the following spring. On hatching, the larvae mine into the leaf petioles and eventually, as they mature, into the root crown. Larvae require a cold period to complete development and, after feeding, larvae leave the rosette to pupate in the soil. About 10-20 larvae can kill a large rosette, 10-20 cm in diameter and only one or two larvae can kill a small rosette (John Ireson, 2018).
Paterson’s Curse Taproot Flea Beetle (Longitarsus echii)
The Paterson’s Curse Taproot Flea Beetle was also released in the Tamar in 2008 and became established in the St Leonards area.
The flea beetle has one generation each year. Adults are mainly active from late autumn to spring. Females commence egg-laying after one to two weeks of feeding and lay their eggs on the taproot of the rosette. Egg-laying can continue until November with females laying an average of 250 eggs. After hatching, larvae feed and mine into the taproot and secondary roots. After feeding, larvae leave the roots and pupate in the soil up to 20 cm below the ground surface. The pupae turn to adults during summer which remain below the ground surface until autumn/winter rain stimulates emergence. The adults then emerge from the soil to start the next generation. Feeding densities of 30-40 larvae will kill rosettes 30-40 cm in diameter. (John Ireson, 2018)
Pollen Beetle (Meligethes planiusculus)
The flower feeding beetles have 1 to 2 generations per year. Adult beetles are dormant over winter and become active in spring on the developing flower stalks. Here they feed, mate and lay eggs. Eggs hatch and larvae bore into the unopened flower buds and feed on the anthers, pollen and ovules. Larvae before the final moult move between flowers and feed on developing seeds. Larvae complete development in 14 to 20 days, then drop from the flowers to pupate in the leaf litter or soil. Adults emerge in around 10 days and return to their host to feed on pollen, developing ovules and maturing seed in open flowers. If adults emerge early enough they may lay more eggs, otherwise they will pass the remainder of the summer and following winter inactive in the leaf litter or soil.
Feeding damage to the flowers and developing seed by adults and larvae results in reduced seed production.
It is important to remember that biological control is a long-term process that will not eradicate Paterson’s Curse. However, the combined attack of complementary biological control agents may reduce vigour, seed output and rate of spread and make them more susceptible to grazing, weather stresses and herbicides as part of an integrated management program.