Stinging caterpillar found at O‘ahu nursery

The stinging caterpillar that has been established on the Big Island since 2001, was found at an O‘ahu nursery recently, according to a state Department of Agriculture press release.

An infestation of nettle caterpillar (Darna pallivitta) has been confirmed and efforts are underway to attempt to contain the infestation in the nursery that is located in a relatively remote area in central O‘ahu.

Workers at the nursery reported getting stung while moving plants from one site to another site on June 1, states the release.

The nursery owner contacted the UH College of Tropical Agriculture & Human Resources and extension agents then informed entomologists with the Hawai‘i Department of Agriculture. The nursery owner was instructed to immediately return all plants to the original site and immediately treat the second site with chemical insecticides. The nursery also began treating the original site with insecticides over the weekend.

Early last week, surveys were conducted by HDOA staff at both sites. The original site was found to be infested with nettle caterpillar and bait stations were deployed. The entire nursery is being chemically treated and surveys and monitoring will continue. No nettle caterpillar were found at the second site, but bait stations were also set.

HDOA is asking residents and nurseries to look out for the nettle caterpillar and report suspected infestations to the state’s Pest Hotline, 643-PEST (7378). Stings from the caterpillar may cause allergic reactions in those who are sensitive to the venom. If stung, treatment recommendations include immediately washing the affected area with soap and water to remove any residue, applying ice to reduce swelling and consulting a physician to determine if further treatment is necessary. Individuals who are sensitive to the venom should seek prompt medical attention, especially if they experience difficulty breathing or if they are stung in the eyes.

Nettle caterpillars grow to about one-inch long, white in color with black bands. The caterpillar has distinct spines that when touched, may cause a burning sensation that lasts about an hour. The adult moth is slightly smaller than a dime and is triangular in shape. It is bicolor with the front two-thirds of the body a yellowish-brown and the posterior third is brownish. The adult flies at night and hides under leaves during the day. The caterpillar has been found primarily on the underside of the leaves of palm plants, grasses and lilies.

After the discovery of the nettle caterpillar in Hilo, HDOA began research on potential biological control agents — natural enemies of the nettle caterpillar that specifically attack this pest without harming native or other beneficial insects and the environment. A predatory insect was found in Taiwan and has undergone testing in HDOA’s Insect Quarantine Facility in Honolulu. HDOA is currently in the process of obtaining approval from federal and state regulatory entities to release the biocontrol insect. This process is expected to take about another six months.

Until then, it is recommended that conventional chemical insecticides labeled for use on ornamental plants be applied to infested plants according to label directions. Insecticides routinely recommended for use to control leaf-feeding caterpillars include carbaryl and acephate. For those who prefer to use a non-toxic pesticide, Bt (Bacillus thuringiensis) sprays have proven to be effective against the larvae of various moths, including the nettle caterpillar. Bt is not toxic to humans, other animals, and the environment.

Nettle caterpillar were first reported at a Hilo nursery on the Big Island in September 2001. It has since spread along the eastern side of the Big Island, but until now had not been found on other islands.

Nettle Caterpillar

Introduction

Specimens of a stinging nettle caterpillar were first found infesting rhapis palm at a nursery in Pana‘ewa on the Big Island in September 2001. They were tentatively identified as Darna pallivitta Moore by D. Tsuda, University of Hawai‘i Insect Diagnostic Clinic, and B. Kumashiro, Hawai‘i Department of Agriculture (HDOA) and confirmed by Dr. M. Epstein of the Smithsonian Institution. This species occurs in Southeast Asia and is known to feed on palms (coconut and areca) and grasses (Cock et al. 1987).

Description

Nettle caterpillars grow to a maximum length of one inch and are covered with spines. A dark longitudinal stripe runs down the back of each caterpillar. The brownish cocoon is round and surrounded by a netting of silk. The adult moth is brown and is one-half inch in length.

Distribution

HDOA has confirmed additional infestation from Hawaiian Paradise Park which is several miles from the known range, indicating that they are probably hitchhiking on plant material. The highest known infestation is in Kurtistown (600 ft. elevation) which likely started in a similar manner. The caterpillar are well established in Waiakea and Waiakea Uka. Infestation in Kea‘au and Orchidland may be a range extension from the Pana‘ewa infestations. All of these sites are either in Lower Puna or South Hilo District.

Damage

The caterpillar have been found feeding on over 45 species of plant in 22 families including Arecaceae, Fabaceae, Poaceae, Agavaceae, Iridaceae, Rubiaceae, Melastomataceae, Apocynaceae, Caryophyllacea, Bromeliaceae, Musaceae, Commelinaceae, Zingiberaceae, Polypodaceae, Hypoxidaceae, Urticaceae, Myrtaceae, Costaceae, Oxalidaceae, Lilaceae, and Euphoribiceae. Fecal pellets on the leaves are signs that the caterpillar is present.

Health concern

The caterpillars are also a health concern due to the stinging spines which cause burning and itching sensations to the skin. Noticeable swelling may occur and welts may form that can last for several days followed by a persistent rash lasting for weeks. If there are any severe symptoms such as difficulty breathing, seek medical help immediately.