Leaf beetles (Paropsines)
S. A. Lawson and J. King
Summary
The paropsine leaf beetles (Coleoptera: Chrysomelidae) include the eucalypt tortoise beetles and eucalypt leaf beetles Paropsis, Paropsisterna and Chrysophtharta and their relatives.
The beetles are rounded in shape and look similar to ladybirds, but have longer antennae.
This DPI&F Note provides information on the biology and management of species which are pests of eucalypt plantations in Queensland.
Damage
Leaf beetle larvae are responsible for the most severe damage. For species such as Paropsis atomaria and Chrysophtharta cloelia, larvae feed almost exclusively on the softer, young growth in the crowns of trees. Defoliation by larvae leads to the typical symptoms seen in Fig. 1, with the crowns taking on a characteristic broom-like appearance. When populations are high they will eat all the new growth, including that on lateral branches.
Fig. 1. Characteristic defoliation
of upper crown by larvae.
Adults feed on leaves, often on older, mature leaves as well as the younger foliage. Feeding damage by adults is identifiable by the 'scalloped' feeding pattern on the edges (margins) of leaves, shown in Fig. 2. Trees are less likely to be severely defoliated by adults, but when populations are high they can cause considerable loss in leaf area of mature foliage, particularly in late summer - autumn.
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Fig. 2. Edge scalloping of leaves caused by adult feeding. |
Fig. 3. Paropsis atomaria adult. |
Beetle species and host trees
Identification
Adult chrysomelid beetles look rather like ladybirds, however the structure
of the antennae is different. Leaf beetle antennae are up to half as long as
the body, slender, usually not thickened at the tips, and usually can be seen.
Ladybird antennae are very short, thickened at the tips and held pressed against
the head, they are difficult to see. It is important to distinguish between
the two because ladybirds are beneficial insects and leaf beetles are pests.
The taxonomy of leaf beetles is highly problematic and so identification of
species is sometimes difficult.
Adults range in size from about 4 mm up to 15 mm in length. Many species are metallic, or pink, yellow, beige, or red. There are also adults with finely patterned elytra (wing covers), some which are strongly patterned with red and black and some plain brown or black species.
Larvae have well developed, dark heads and three pairs of legs, most are pale in colour, some with dark stripes along the body.
Important Queensland species
Paropsis and Paropsisterna beetles feed on eucalypts, and are often called the eucalypt tortoise beetles. Paropsis species vary in size and colouring, many are brightly coloured, with intricate patterns on the elytra but the colours fade in dead beetles. The most common species in Southeast Queensland is Paropsis atomaria (Fig. 3), which is a serious pest of eucalypt plantations, particularly of E. cloeziana (Gympie messmate), but it can attack a very wide host range of eucalypt species.
Another common species observed in eucalypt plantations, although not at damaging levels, is Paropsis variolosa. Some of the larger species of Paropsisterna are shining brown or black and some have a few large red or orange spots on a black or brown background. Species of Paropsisterna have been observed in some eucalypt plantations, though not at damaging levels.
Chrysophtharta
The larvae and adults of Chrysophtharta also feed on eucalypts. Chrysophtharta bimaculata is a major pest of eucalypts in Tasmania, but has not been recorded as a pest in Queensland. Of major concern in Queensland is C. cloelia, which has been recorded on a number of eucalypt species including E. pilularis (blackbutt), E. robusta (swamp mahogany), E. pellita (large fruited red mahogany), E. grandis (rose gum), E. dunnii, (Dunn's white gum), E. tereticornis (forest red gum), E. camaldulensis (river red gum) and on hybrids of the latter two species with E. grandis .
Fig. 4. Chrysophtharta cloelia adult.
Distribution
Paropsine leaf beetles are widely distributed throughout Queensland and southeastern Australia. Due to the huge diversity of species and our current poor knowledge of the taxonomy of them, distribution of individual species is not well known.
Of the species that are pests of eucalypt plantations, Paropsis atomaria is common and widely distributed throughout Southeast Queensland and further south, as is P. variolosa. Neither of these species is common in Far North Queensland.
Chrysophtharta cloelia is also widely distributed in Southeast Queensland and further south, and also occurs commonly in Far North Queensland, where it is probably the most important leaf beetle pest of eucalypts.
Life cycle
Adults feed singly. However, there can be many adults and larvae feeding on one host tree. Adults are active in the spring and summer in cooler climates and all year round in the tropics. In cooler climates adults over-winter in sheltered places, for example under bark, and begin egg-laying in spring.
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Fig. 5. Paropsis atomaria laying egg collar on young shoot. |
Fig. 6. Chrysophtharta cloelia laying egg raft on leaf. |
Eggs are laid directly onto leaves or stems, usually on or near new growth. The eggs are cemented onto leaves in patterns characteristic of the species: singly, or end to end in a neat line, or side by side in rows or in a 'collar' round a leaf stem or slender twig (see Figs 5 and 6). Eggs are very vulnerable to predators such as ladybirds, predatory bugs and tiny wasp parasites.
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Fig. 7. Young Paropsis atomaria larval group feeding on eucalypt leaf. |
Fig. 8. Mature Paropsis atomaria larvae in defensive pose. |
Newly hatched larvae feed in a group (Fig. 7), at first grazing patches on the leaf surface. As the larvae grow they may stay in a group or feed by themselves. At this stage leaves are often chewed down to the central vein. Fully developed larvae move down the tree to pupate in the soil.
Larvae of many paropsines defend themselves by producing a toxic compound from glands close to the hind end. Disturbed larvae will tap their 'tails' on the leaf and then lift the hind end of the body and exert finger-like defensive glands (Fig. 8). The compound is a powerful deterrent to predators such as ants.
In the tropics and subtropics the adults and larvae are present all year round, but they are most active in summer. In cooler parts of the state they overwinter as adults from about May to September and begin feeding on new growth and lay eggs as the weather warms up in early spring. For example, the most common species in Southeast Queensland, Paropsis atomaria, appears to have 2-3 generations/year. These generations overlap, so all stages, adults, eggs and larvae, are present throughout the active season.
Management
Effective management of leaf beetles, as with other pests, requires regular inspection of plantations, particularly while the trees are in their first two growing seasons. When signs of damage have become obvious (e.g. severe crown defoliation) it is often too late to take remedial action. For P. atomaria and C. cloelia in Southeast Queensland there are usually 2 defoliation events per year: in late December-early January and late March to May. Monitoring of larval numbers on trees should thus be more intensive in the several weeks before these peaks, the aim being to be able to make a decision on control before significant damage is done.
Biological control
Eggs and larvae are eaten by a variety of natural enemies, including ladybirds and predatory bugs (Fig. 9), and are parasitised by wasps and tachinid flies. Small numbers of pests can be monitored for parasites and predators, and further action can be considered if pest numbers increase beyond the capacity of the natural enemies to control them.
The
action of these predators and parasitoids often lags behind the development
of the beetle population, due to the natural enemies having to play 'catch-up'.
In the meantime, severe defoliation can result.
Fig. 9. Predatory pentatomid bug feeding on leaf beetle larva.
Insectivorous birds have also been observed feeding on leaf beetle larvae in plantations and are potentially important control agents. Again, there may be considerable lag between the appearance of the pest and the arrival of the birds and this is also dependent on the availability of other food for birds in the area.
Manual control
On ornamentals or for small numbers of trees, adults and larvae can be collected into soapy water in a bucket. Adults tend to drop to the ground if disturbed. Eggs can be scraped off shoots and larvae hosed off foliage. Inspections should continue after they have been removed in case any were missed.
Regular monitoring of plantations is essential to determine changes in the abundance of the critical stages (eggs, young larvae, older larvae, adults).
Chemical control
At the time this guide was prepared, two insecticides, namely Dominex 100 and Saboteur 400, were registered for use against leaf beetles in eucalypt plantations in Queensland. Note: This information was correct at the time of publication. However, it is the user's responsibility to ensure that registered agricultural chemicals are used in accordance with legal requirements (see Further Information). Always read the label.
Chemical applications should only be considered if defoliation is severe enough (> 50% defoliation) to cause an unacceptable loss of growth or tree mortality. Most eucalypts can tolerate levels of defoliation of up to 40-50% without economically significant loss of growth.
Further Information
Infopest CD-ROM contains current national information on registered agricultural chemicals and is available from Infopest, DPI&F, GPO Box 46, Brisbane Qld 4001 or by email from infopest@dpi.qld.gov.au
Elliott, H.J., Ohmart, C.P and F.R. Wylie (1998). Insect Pests of Australian Forests: Ecology and Management. Inkata Press. 214pp.
Farrow, R. (1996). CSIRO Identification Leaflets - Insect Pests of Eucalypts on farmland and in plantations in southeastern Australia. No. 6. 4pp. CSIRO Publishing.
State Forests of NSW (1995). Leaf Beetles Forest Protection Series. Leaflet E6, 4pp.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Last reviewed 7 April 2006
