First Record of Fossorial Behavior in Hawaiian Leafroller Larvae, Omiodes continuatalis (: )1

Cynthia King2,3 and Daniel Rubinoff 3

Abstract: Larvae of the endemic Hawaiian leafroller moth, Omiodes continuatalis (Wallengren), were used in controlled exposure trials on the island of Maui, Hawai‘i, in May–August 2006, to examine effects of introduced parasitoids on native Hawaiian Lepidoptera. During the trials we observed O. continuatalis larvae burrowing up to 14 cm into the soil beneath plants on which they were deployed. This discovery reflects the first record of fossorial behavior not asso- ciated with pupation in larvae of Hawaiian Omiodes and suggests how O. con- tinuatalis, a species once listed as extinct by the U.S. Fish and Wildlife Service, may persist despite intense pressure from introduced biological control agents.

Omiodes continuatalis (Wallengren)isan to Omiodes species disappearances because endemic crambid leafroller moth, historically two endemic Hawaiian Omiodes species were distributed throughout the main Hawaiian the direct targets of biological control pro- Islands. The species was noted by Thomas grams (Funasaki et al. 1988). Omiodes accepta Blackburn to be the most common moth en- (Butler), the sugarcane leafroller, and O. countered during his collecting trips before blackburni (Butler), the coconut leafroller, 1880 (Zimmerman 1958). A century later, became important economic pests in their re- O. continuatalis and an additional 13 species spective crops and were the subject of multi- in the Omiodes were listed as extinct or ple biological control releases between 1895 possibly extinct by the U.S. Fish and Wildlife and 1958 (Funasaki et al. 1988). After the re- Service and other agencies (Gagne´ 1982, leases, high rates of parasitism were observed Gagne´ and Howarth 1985, Evenhuis 2002, in populations of target as well as nontarget IUCN 2003). Likely reasons cited for their Omiodes species, and biological control agents extinction were loss of habitat and decline of were implicated in subsequent species de- native host plant species, as well as the non- clines and disappearances (Zimmerman 1958, target impacts of exotic parasitoids intro- Bess 1974). duced for biological control programs A review of unidentified material in mu- (Gagne´ 1982). The nontarget impacts of in- seum collections and additional field surveys troduced parasitoids are particularly relevant has resulted in the rediscovery of O. continua- talis and four other Omiodes species previously 1 This project was funded by a U.S. Department of listed as extinct (Haines et al. 2003). Al- Agriculture (USDA) Cooperative State Research, Educa- though the distribution and abundance of tion, and Extension (CSREES) Special Research Grant O. continuatalis has been dramatically reduced Tropical and Subtropical Agricultural Research (USDA (Blackburn cited in Zimmerman 1958), the CSREES Award no. 2004-34135-14998). Additional funding was provided by USDA CSREES project species persists on Maui, Kaho‘olawe, and HAW00942-H and HAW00956-H. Manuscript accepted Hawai‘i Island and can be locally abundant 3 May 2007. (W. Haines, unpubl. data). However the re- 2 Corresponding author (e-mail: cbaking@hawaii discovery of a few of the presumed extinct .edu). species of Omiodes has not lessened concerns 3 Department of Plant and Environmental Protection Sciences, 310 Gilmore Hall, 3050 Maile Way, University over the impacts of introduced parasitoids of Hawai‘i at Ma¯noa, Honolulu, Hawai‘i 96822. (Howarth 2000), and biological control agents have been documented parasitizing a Pacific Science (2008), vol. 62, no. 1:147–150 growing array of native Hawaiian Lepi- : 2008 by University of Hawai‘i Press doptera (Henneman and Memmott 2001, All rights reserved Oboyski et al. 2004). More ominous, bio-

147 148 PACIFIC SCIENCE . January 2008 logical control agents have infiltrated largely ployment and after retrieval from the field to native montane habitats not previously con- confirm the larval instar at release and re- sidered at high risk of invasion (Henneman trieval. Larvae and plants were retrieved and and Memmott 2001). replaced after approximately 4 days of expo- To quantitatively assess the relative threat sure. Field trials were conducted at five sites exotic parasitoids pose to endemic moth on East Maui: Hawai‘i Commercial & Sugar species, we initiated controlled exposure ex- (HCS) Ha¯li‘imaile sugarcane field (274 m periments on the island of Maui from May elevation), lower Makawao Forest Reserve to August 2006. As part of this study, we (914 m), University of Hawai‘i (UH) Kula recorded O. continuatalis larval behavior for Agricultural Research Station (975 m), upper all instars. Through detailed observations of Makawao Forest Reserve (1,280 m), and Ha- more than 800 individual larvae, we recorded leakala¯ Ranch (1,280 m). previously unknown behavior that may bear directly on the level of native moth vulner- results and discussion ability to introduced parasitoids. Early obser- vations of O. continuatalis indicate that the On at least 12 occasions, when attempting to larvae hide intermittently in leaf litter accu- retrieve larvae from sugarcane foliage we mulated at the base of grasses and generally discovered that larvae were not present on prefer to feed on foliage on the lower portion the plant. Instead, O. continuatalis larvae were of plants (Swezey 1907). Many of the trial found well below the surface of the soil. larvae exhibited this typical behavior, but on These fossorial larvae were found at depths numerous occasions O. continuatalis larvae ranging from 5.5 to 14 cm below the soil were also observed hiding underground. The surface. Omiodes continuatalis larvae progress purpose of this note is to describe the nature through 9–10 developmental instars, so it is of this newly recognized fossorial behavior notable that individuals retrieved from under and to discuss the potential implications of the soil ranged from third to fourth instar such behavior on the ability of species to sur- (head capsule width: 0.625–1.9 mm) and vive the pressures of introduced parasitoids. were not the most mature larvae utilized in the trials. The developmental stage of these materials and methods larvae discounts the likelihood that individu- als burrowed into the soil to pupate. Previous Laboratory colonies of O. continuatalis were observations of the species indicate that even established using female captured when preparing to pupate, O. continuatalis from ultraviolet light traps set on Ka‘ili‘ili may retreat to the base of the plant on which Road in Kokomo, Maui (484 m). Omiodes con- they are feeding and web together soil and tinuatalis adults were placed in sleeve cages leaf matter to create a shelter before pupating with potted sugarcane plants and housed in a but remain at the soil surface (Swezey 1907; greenhouse at the University of Hawai‘i Kula C.K., pers. obs.). We observed the fossorial Agricultural Research Station on Maui. Fe- behavior at the Ha¯li‘imaile sugarcane field, male moths oviposited readily, and resultant UH Kula Agricultural Research Station, larvae were reared. Before our nontarget Haleakala¯ Ranch, and Makawao Forest Re- parasitism field trials, one to four larvae of serve (1,280 m) field sites. Additional records various instars were transferred onto young of fossorial behavior would likely have been sugarcane plants. Each plant was propagated documented, but such behavior has not been in potting soil (Sunshine Mix 5) and con- recorded previously and was not initially sus- tained within 12.7 by 15.2 cm plastic pots. pected to be the reason for larval ‘‘disappear- These sugarcane plants were then transported ance.’’ Consequently, early in the trials, larval to field sites and placed inside predator exclo- absence was attributed to unknown mortality sures that prevented mammals, ants, and birds when, in fact, larvae may simply have been from removing the larvae. The head capsule underground. width of each larva was measured before de- Body coloration provides an indication of Fossorial Behavior in Omiodes continuatalis Larvae . King and Rubinoff 149 how fossorial larvae may have been spending species or populations that have burrowing their time. Omiodes continuatalis larval body larvae. The burrowing observed in the O. con- color directly reflects recent dietary intake; tinuatalis larvae in our study may reflect the larvae feeding on green or yellowing foliage tendency of a local population rather than are colored accordingly. If the larvae discov- a widespread ability because the larvae used ered underground were staying there and in our field trials originated from a single feeding on plant roots or dried foliage at the Kokomo population, though this would be base of the sugarcane plant, they would have an improbable coincidence. However it is pos- appeared light yellow or brown, however all sible that specific stimuli facilitate or inhibit of the larvae retrieved from beneath the soil larvae from hiding underground. Further- exhibited a vivid green body. Their green col- more, species of Omiodes that occur on the oration indicates that larvae were not feeding leaves of arborescent host plants, such as ba- below the ground but periodically moving nana and palms, or epiphytic host plants, such up from beneath the soil to feed on green as the native Hawaiian lilies, probably do not foliage. have the opportunity to hide in soil and may The larvae of many crambid species are therefore be more vulnerable to predators known to be fossorial (Landry 1995); how- and parasitoids. If this behavior is unique to ever this represents the first documented evi- certain taxa, it could help explain why some dence of fossorial behavior in any Hawaiian species of Omiodes have persisted, albeit in re- Omiodes and has important practical and evo- duced numbers, while other species seem to lutionary implications. Our observations sug- have truly gone extinct. gest that the behavior is not associated with pupation. To date, we have observed hun- dreds of larvae across five generations pupat- acknowledgments ing in plant foliage and at the soil surface but We thank A. Arcinas (Hawai‘i Agricultural never below the soil surface. Instead, the bur- Research Center) and M. Nakahata (Hawai‘i rowing behavior may function as a facultative Commercial & Sugar Company) for provid- response to predation and parasitism that has ing plant material, and D. Oka and G. Otani been present in Hawai‘i throughout the evo- (University of Hawai‘i Kula Agricultural lution of Hawaiian Omiodes and may be trig- Research Station) for field preparation and gered under certain conditions in segments of greenhouse assistance. K. Camp, J. McNas- the population. A decreased risk of predation sar, and J. Muir provided essential field assis- and parasitism and subsequent increase in lar- tance. Access permits were granted by S. val survivorship is a potential benefit to indi- Meidel (Haleakala¯ Ranch), and G. Shishido viduals and species exhibiting the behavior. and B. Gagne´ (Department of Land and Nat- Hiding underground could provide tempo- ural Resources, Division of Forestry and rary refuge not only from parasitoids but Wildlife). Special thanks to M. Wright and also from predators including wasps and spi- C. Hooks (University of Hawai‘i, Depart- ders. It is possible that burrowing behavior ment of Plant and Environmental Protection may have been triggered as a result of unnat- Sciences) for valuable input on study design, ural conditions created by exclosures and a and also W. Haines (University of Hawai‘i, novel potted plant substrate. However, many Department of Plant and Environmental of our observations are consistent with the Protection Sciences) for access to unpub- documented tendency of O. continuatalis lished data. Two anonymous reviewers pro- larvae to shelter and feed at the base of host vided valuable feedback on this publication. plants, and fossorial behavior is commonly observed in other crambid larvae. The frequency and distribution of fosso- Literature Cited rial behavior across species in the genus Omi- odes are unknown but could have important Bess, H. A. 1974. Hedylepta blackburni (But- implications for the persistence of particular ler), a perennial pest of coconut on wind- 150 PACIFIC SCIENCE . January 2008

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