Nettle Caterpillar

Nettle Caterpillar [Darna pallivitta Moore]. 

D. pallivitta, after dispersing from its initial infestation site in Panaewa to Waiakea and Hilo in the South Hilo District and to Keaau, Kurtistown, and the Hawaiian Paradise Park (HPP) Subdivision in the Upper Puna District during FY 05, continued to steadily extend its range of infestation. In FY 06, the nettle caterpillar was commonly found in residential areas of Waiakea and Hilo and became widespread in HPP, extending southeastward into the Ainaloa Estates Subdivision. However, it is still confined to the southeastern portion of the Island of Hawaii. Reports of sightings have been made on few occasions in Kona but none have ever been confirmed. 

Pest calls regarding this stinging caterpillar increased in mid-July 2005, mostly from HPP. This area is rapidly being developed so substantial numbers of landscaped house lots occur there now.   In September, many calls continued to be received from HPP, but also from Waiakea, Waiakea Uka, and Kaumana. A total of 27 were received that month, most as a result of stinging incidents. Light trap counts of adults in HPP made by volunteers suggested some synchrony of the life cycle. The numbers of moths caught at lights were highest in September, following the outbreak of larvae. By November, only a single call was received, regarding  the caterpillars. 

In a cooperative effort with HDOA-PPC Branch personnel in Hilo, Dr. Matthew Siderhurst (USDA-ARSPBARC), funded by the Hawaii Invasive Species Committee (HISC), developed a pheromone lure for D. pallivitta males. Lures given to Hilo PPC personnel for trials were set out in Kona to try to confirm recent reports of the nettle caterpillar at three different sites.  No moths were captured in the traps at any of the sites so its presence in Kona remains unconfirmed. 

Rearing of D. pallivitta in the Hilo Insectary continued to be a difficult challenge due to the infection of the larvae by a nuclear cytoplasmic polyhedrosis virus. It has become a routine practice to kill off the colony after enough pupae are collected because the infection becomes epidemic in the rearing cages. All supplies and equipment must then be sterilized and the colony restarted using eggs from the emerged moths of the last generation.   Nonetheless, the Hilo Insectary has so far been able to keep the HDOA Insect Quarantine Facility (IQF) in Honolulu supplied with larvae as needed for rearing the parasitoid that was introduced from Taiwan. 

Exploration for nettle caterpillar natural enemies in Taiwan during October 2004 resulted in the collection of a parasitic wasp, Aroplectrus dimerus Lin (Eulophidae) that was found attacking D. pallivitta larvae. Host-specificity testing in the IQF was conducted to determine if this potential biological control agent will attack any non-target species, mainly native Hawaiian caterpillar species or species that have been introduced as weed biocontrol agents.  The testing was completed and a report of the results is being written for submission to the Board of Agriculture to request the release of this biocontrol agent from quarantine.

Propagation of the parasitoid A. dimerus is continuing in the IQF, however, it is greatly dependent on shipments of D. pallivitta larvae from the Hilo Insectary.  Laboratory conditions appear conducive to the spread of the virus that has plagued the D. pallivitta colonies for several years. After rearing the larvae for one generation in the laboratory, the colony becomes badly diseased and propagation stock is needed for further colonization. Thus, supplemental larval shipments are routinely sent from the Big Island, where the virus disease is less prevalent but still an ongoing problem.