PHENOLOGY, OCCURRENCE AND INSECTICIDAL CONTROL OF RHYPARIDA NITIDA – A PEST IN SOUTHERN QUEENSLAND

Larvae of rhyparida beetles bore into the bases of newly ratooning shoots, causing dead hearts. Very minor damage will kill ‘surplus’ shoots, while more intense damage appears to set plant growth back and causes some yield loss. Prolonged attack will kill all shoots and kill the stool, leaving large gaps and necessitating replanting. No insecticide is registered for control of the pest and cultural controls are unknown. The project developed a better understanding of the phenology of Rhyparida nitida – this species has a 1 year lifecycle with extended oviposition over summer, slow development of small larvae during autumn and winter and more rapid development of larger larvae during spring. The extended oviposition means that each generation has individuals of widely varying ages. In field surveys over 2 years, there were no consistent associations of farming practices with numbers of rhyparida larvae. This is consistent with an insect that has adults that are very mobile and are nonselective for oviposition. When Furadan® was coultered into the soil, it did provide some control of larvae, but did not improve subsequent yield of cane. Confidor® and Nemacur® did not provide any significant control or yield increase. These results indicate the compensatory ability of the sugarcane plant following damage and the difficulty in timing applications to adequately target larvae. The success of the project was hampered by generally low populations of rhyparida. This indicates that the pest is likely to remain of minor importance within the Bundaberg-Isis area. As such, the returns from further work are likely to be low.