Weevils

Rank & taxon

Family Curculionidae (excluding ambrosia beetles)

Description

Weevils are most diverse family in the world, occuring from the poles to the tropics, and feeding on all types of plants. They may range in size from around 1-50 mm long, and palm-associated weevils span the entire range. Most can be easily recognized by the elongated rostrum, or snout, bearing small mandibles at the tip. Another distinctive feature of weevils is their elbowed, club-shaped antennae. Weevils generally have 5-segmented tarsitarsi:
the portion of insect legs distal to the tibia (singular tarsus)
, though one segment is often so small that the tarsitarsi:
the portion of insect legs distal to the tibia (singular tarsus)
appear 4-segmented instead. Aside from these features, the morphological and biological diversity within the family is, as one might expect, immense. Larvae possess a large head capsule with correspondingly large mandibles, are legless, and move peristaltically. They are usually whitish or cream-colored, but often turn an orange-yellow color prior to pupation. Late instarinstar:
stage in an insect's life history between any two molts. The newly hatched insect is the first instar, and the adult (imago) is the final instar.
larvae may be significantly larger than the imagoimago:
the adult stage of an insect
, up to 64 mm long and 25 mm wide.

Distribution

Worldwide; over 4,600 genera, more than 51,000 described species

Biology/life cycle

Adult weevils are usually cryptic, taking refuge in sheltered areas of the palm, such as unopened inflorescences, petiole bases, floral peduncles, or larval-damaged areas in the crown and/or stem. Most palm-associated weevils chew an oviposition site with their mandibles, and deposit 30-400 eggs in specific plant tissues, depending upon the species. Larvae usually go through 5 to 10 instars prior to pupating, making a cocoon from host fibers. Weevils are often borers of palms, but many are considered beneficial, serving as pollinators.

Hosts

Palms: a wide variety of palm species

Other: nearly every plant species

Representative taxa on palms

Rhynchophorus palmarum, a large weevil (around 50 mm in length), is one of the most significant pests of plantations of Cocos nucifera (coconut palm) and Elaeis guineensis (African oil palm) in Central America. Large larval infestations can be lethal to adult palms.

Dynamis borassi, frequently confused with R. palmarum, is a pest of coconut palm in several South American countries. It usually attacks and destroys unopened inflorescences.

Additional comments

Palm and sugar cane weevils (Rhynchophorus palmarum, Dynamis borassi, and Metamasius hemipterus) in tropical America can be vectors for red ring nematode (Bursaphelenchus cocophilus), the causal agent of a potentially lethal disease, red ring disease. The nematode may also cause a chronic condition known as "little leaf," which can eventually lead to red ring disease. Coconut palm varieties are particularly susceptible to infestations of both the weevils and the nematodes, though African oil palm and date palm (Phoenix spp.) may also be affected.