Northern citrus root weevil

Scientific name

Pachnaeus opalus (Coleoptera: Curculionidae)

Similar species

southern citrus root weevil, Pachnaeus litus

The southern citrus root weevil, Pachnaeus litus is found in southern Florida, but the distribution of the northern citrus root weevil and the southern citrus root weevil overlap in central Florida. The northern citrus root weevil and the southern citrus root weevil look almost identical, but the southern citrus root weevil has a visible notch on the pronotumpronotum:
the dorsal surface of the first thoracic segment
, and the northern citrus root weevil has a smooth pronotal edge.

Distribution

United States: eastern United States.

Worldwide: Mexico.

Native to the eastern United States.

Diagnostic characteristics

Adults

• Snout-like mouthparts.
• Hardened forewings (elytra) cover the abdomenabdomen:
  one of the three body segments in insects; the most posterior segment containing the heart, reproductive organs, and digestive organs
  when at rest.
• Bright blue-green, aqua, or gray in color.
• Size of adults is 8.5 - 14 mm (0.33 - 0.55 in.) in length.

Larvae

• White, grub-like insects with well-developed brownish-black chewing mouthpartschewing mouthparts:
  mouthparts designed for biting and chewing; mandibles move from side to side with overlapping edges that cut like scissors as well as surfaces for grinding; characteristic of orthopterans <a href="http://idtools.org/id/citrus/pests/morphology.php?state[]=head#mouthparts"></a>
  .
• Size ranges from 12.7 - 25.5 mm (0.5 - 1.0 in.) in length.

Eggs

• Egg masses consist of 25 - 50 eggs.
• Cylindrical.
• Cream-colored to transparent.

Hosts

Citrus hosts

All Citrus species and their hybrids

Non-citrus hosts

Northern citrus root weevil has been identified on 27 different hosts in Florida with no particular affinities for certain plant families.

Host damage

Leaves

• Eggs are laid in masses on mature leaves.
• Leaves may be held together by a gelatinous substance which protects the eggs.
• Eggs hatch in about 7 - 10 days.
• Adults feeding on foliage result in marginal notching of leaves on young, tender shoots.
• Leaf injury by adult weevils seems to be a minor problem only associated with young trees and has no apparent effect on mature trees.

Roots

• Newly hatched larvae fall from the leaves and burrow into soil to feed on the roots of citrus trees.
• Larval feeding results in a weakened and stressed tree.

Biology

A female lays about 4,000 eggs in her lifetime. Adults usually emerge from the ground mid-May through mid-July. Eggs are laid directly on the host planthost plant:
the plant the provides sustenance for an insect
foliage and hatch in 7 - 10 days, depending on the moisture level. Larvae drop to the ground to feed underground on the roots for about one year then pupate below ground. Throughout the year, adults can be found in the early morning and late afternoon but move deeper into the canopycanopy:
referring to the crown of a tree that includes the leaves, stems, and branches
during the day. An adult lifespan is 100 - 120 days.

References

Duncan, L.W., M.E. Rogers, C.W. McCoy, S.H. Futch, J.H. Graham, and H.N. Nigg. 2011. Florida Citrus Pest Management Guide: Citrus Root Weevils. University of Florida. (http://edis.ifas.ufl.edu/cg006).

Authors

Weeks, J.A., A.C. Hodges, and N.C. Leppla