Swarming leaf beetles

Swarming leaf beetle

Swarming leaf beetles damage

Scientific name

Rhyparida spp.

Description of adult

Swarming leaf beetles (Rhyparida spp.) are small (3–5mm), shiny, brown or black insects that swarm after the first heavy rains of the season. A number of species are involved but they all have similar habits.

Immature stages

Eggs are laid in the soil and hatch into small larvae similar in shape to white grubs.

Life history

The larvae feed on the roots of grasses for some months before pupating. Heavy rain allows emergence of the beetles from the soil.

Distribution

Found in all districts but more common in north Queensland.

Host range

The wide host range includes:

• commercial crops such as avocado, lychee, rambutan, durian, mangosteen and other rare fruits, maize, sugarcane,
• various ornamentals
• native trees, especially cadaghi (Eucalyptus torelliana) and lemon-scented gum (Eucalyptus citriodora)
• pasture species.

Damage

Major and sporadic. A serious pest in some localities, particularly where orchards are adjacent to pastures or sugarcane or in wet tropical coastal areas.

This insect causes damage to chempedak, cocoa, durian, grumichama, jaboticaba, jackfruit, longan, marang, mangosteen and rambutan. Swarms of this insect can cause severe damage to the new terminal growth on a range of crops. Damaged terminals have a burnt look. Development in young trees can be severely retarded. Occasionally developing fruits are attacked.

Control

These beetles can be difficult to detect as they hide under leaves during the day, coming out to feed at night. Shake branches over a bucket when trees start to flush in spring. If several beetles are recovered, action is warranted. In areas where attacks occur yearly, protect new growth on young trees as early as possible. Older bearing trees can normally tolerate damage.

Cultural

Beetle swarms generally occur during the spring to summer period after the first storms of the season. Cadaghi (Eucalyptus torelliana) is a favoured host and control of beetle swarms on this tree is sometimes possible before they invade orchards.

Chemical

Apply an insecticide treatment as soon as swarms invade the orchard. Repeat treatments may be necessary if reinfestation occurs.

Check the Australian Pesticides and Veterinary Medicines Authority database for chemicals registered or approved under permit to treat this pest on the target crop in your location. Always read the label and observe withholding periods.