Phenology of Eucalyptus weevil, Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae), and chrysomelid beetles in Eucalyptus globulus plantations in south‐western Australia

Abstract

1 In south-western Australia, Eucalyptus globulus plantations are defoliated by a complex of beetle species, yet only scant information exists on these species under such climatic conditions. To improve management of these defoliating beetles in the region, canopy fogging and shoot clipping were conducted in plantations between 1999 and 2002 to identify and document the phenology of the beetle species present. 2 Eucalyptus weevil, Gonipterus scutellatus , was the most common and destructive defoliating beetle. Gonipterus scutellatus undergoes one principal generation each year with a lesser second generation or cohort in some seasons, which contrasts greatly with reports of two to four annual generations for the species in other regions. This limited reproduction by G. scutellatus may be due to the limited availability from summer onwards of new flushing foliage, which is essential for feeding and oviposition. 3 Several species of chrysomelid beetles were collected in plantations, but these were present in much lower numbers than G. scutellatus and were only a minor concern. However, some species, such as Chrysophtharta variicollis , appear to be capable of developing short-lived outbreaks. 4 A diverse suite of natural enemies was fogged from plantations but they were significantly less abundant than defoliating beetles and are not likely to provide significant control of beetles. 5 In terms of managing these defoliating beetles, monitoring and control should focus on G. scutellatus , and be conducted during spring when most damage occurs.

Effects of defoliation by Eucalyptus weevil, Gonipterus scutellatus, and chrysomelid beetles on growth of Eucalyptus globulus in southwestern Australia

“…Rather than estimating defoliation to foliage in the upper 50% of the tree, or the upper crown as it is often referred, defoliation of the adult-phase foliage was estimated at the growing tip of the tree containing only new season's foliage, because this was where beetle feeding was concentrated, and where defoliation has the greatest impact on tree growth and form. Only low levels (generally <10-20%) of defoliation were recorded to the lower crown and to juvenile-phase foliage during the trial (Loch, 2006). Estimates of foliage and defoliation were made to the nearest 10% with smaller graduations near 0% (i.e., 0%, 2%, 5%, 10%) and 100% (i.e., 90%, 95%, 98%, 100%).…”

“…In southwestern Australia, another defoliating beetle, the Eucalyptus weevil, Gonipterus scutellatus Gyllenhal, has been identified as the most damaging insect pest of established plantations of E. globulus Labill. (Loch and Floyd, 2001;Loch, 2005Loch, , 2006. However, a recent study has shown that what has been identified as G. scutellatus worldwide is a complex of more than 10 cryptic species (T. Mapondera, T. Burgess, R. Oberprieler, M. Matsuki, unpublished data).…”

“…and Cadmus excrementarius Suffrian, and nocturnal scarab beetles also cause some defoliation to established E. globulus plantations in southwestern Australia (Loch, 2006). Paropsisterna spp.…”

“…The species encountered during this study was a G. scutellatus species that had been accidentally introduced from southeastern Australia. This species undergoes one principal generation each year with a lesser second generation or cohort in some seasons (Loch, 2006). Adults and larvae cause similar damage to chrysomelid beetles by feeding on the new developing eucalypt leaves, buds and shoots of the upper crown.…”

Do artificial and natural defoliation have similar effects on physiology of Eucalyptus globulus Labill. seedlings?

“…), Paropsisterna agricola (Chapuis), Mnesampela privata (Guenée), Uraba lugens (Walker), Cadmus australis and Gonipterus scutellatus Gyllenhal are among the most important defoliators of established E. globulus plantations throughout Australia (Floyd et al, 2002;Loch, 2006;Loch and Floyd, 2001). These herbivores feed on new shoots and mostly juvenile leaves of eucalypts, which if of sufficient magnitude can lead to the characteristic damage of the upper crown called the "broom-topping effect" (Loch, 2005).…”