Can Hawaiian Carnivorous Caterpillars Attack Invasive Ants Or Vice Versa?
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Can Hawaiian carnivorous caterpillars attack invasive ants or vice versa? Shinji Sugiura1,2 1Department of Forest Entomology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan 2Center for Conservation Research and Training, Pacific Biosciences Research Center, University of Hawaii, 3050 Maile Way, Gilmore 408, Honolulu, HI 96822, USA E-mail: [email protected] The Hawaiian Islands have allowed insects to evolve (Meyrick) preyed on a braconid parasitoid. Although unique habits, such as ambush predating in caterpillars1 phytophagous Eupithecia are frequently parasitised by and ground-dwelling in damselfly nymphs2, because the parasitic wasps and flies, the carnivorous species of islands are isolated and originally lacked predators, such Eupithecia are rarely parasitised, suggesting that as ants and wasps3. However, many exotic species have carnivorous Eupithecia counterattack the parasitoids4,5. been introduced to the islands through human activities, However, spiders may defend against Eupithecia attacks; which has affected the native fauna3. one spider, Theridion grallator Simon, was attacked by Ambush carnivorous caterpillars (Eupithecia spp.; E. orichloris, but the spider escaped from the E. Lepidoptera: Geometridae) provide a remarkable orichloris by biting it4. Similarly, ants with strong example of a feeding behaviour unique to the Hawaiian mandibles may counterattack Eupithecia larvae4. Islands1,4. More than 20 endemic species of Eupithecia However, it is unclear whether Eupithecia can attack have been recorded from the Hawaiian Islands1,4. While ants. the larvae of two Eupithecia species are herbivores, the Here, I examined whether E. orichloris can attack ants larvae of other species on the islands are obligate under laboratory conditions (21°C). An E. orichloris predators1,4. The larvae of carnivorous Eupithecia perch larva (body length, 19.3 mm) and workers of the invasive inconspicuously along leaf edges (Fig. 1a) and stems and ant Pheidole megacephala (Fabricius) collected from seize arthropods that touch their posterior body section1. Oahu Island in early June 2010 were used for the Their prey includes various arthropods species, such as experiment. Pheidole megacephala has minor (body springtails, drosophilid flies, cockroaches, crickets, length 2 mm) and major (3.5 mm) forms of workers; psocids, moths, and leafhoppers1,4. Eupithecia larvae major workers have larger heads with stronger mandibles even attack predatory arthropods. For example, than minor ones6. First, I used forceps to place a minor Montgomery4 reported that Eupithecia orichloris worker of P. megacephala on a leaf where E. orichloris Nature Precedings : doi:10.1038/npre.2010.5374.1 Posted 8 Dec 2010 Figure 1. a An Eupithecia orichloris larva perching on a leaf; b E. orichloris feeding on a minor worker of Pheidole megacephala; c The body of the minor worker was torn apart in the E. orichloris attack (the arrow indicates the removed abdomen); d E. orichloris was counterattacked by a major worker of P. megacephala (the arrow indicates the biting by P. megacephala); e The major worker escaped from the E. orichloris attack; f E. orichloris lost a foreleg as a result of the bite by the major worker (arrow). 1 perched. The E. orichloris was observed to bend the seized the ant the instant the ant touched its posterior ACKNOWLEDGEMENTS. I thank Vincent Costello body. The caterpillar seized the ant using its thoracic and Brenden Holland for providing the caterpillar. The (elongated spiny) legs (Fig. 1b), and then used its author was supported by a JSPS Postdoctoral Fellowship mandibles to tear the ant body in two (Fig. 1c). Thus, E. for Research Abroad. orichloris can successfully attack the minor workers of P. megacephala. The next day, I similarly placed a major REFERENCES worker of P. megacephala on a leaf where E. orichloris 1. Montgomery, S. L. GeoJournal 7, 549–556 (1983). perched. The E. orichloris was also observed to attack 2. Zimmerman, E. C. Insects of Hawaii vol. 2: the ant the instant the ant touched its posterior end. Apterygota to Thysanoptera, University of Hawai‘i However, the ant counterattacked (Fig. 1d) and was Press (1948). observed to bite one of the thoracic legs of E. orichloris 3. Ziegler, A. C. Hawaiian Natural History, Ecology, (Fig. 1d) and ultimately escaped (Fig. 1e). The E. and Evolution, University of Hawai‘i Press (2002). orichloris lost a foreleg and consequently lost its ability 4. Montgomery, S. L. Carnivorous caterpillars: the to seize prey (Fig. 1f). The caterpillar died 10 days later. systematics, behavior, biogeography and The Hawaiian Islands, which originally lacked ants, conservation of Eupithecia Curtis (Lepidoptera: have recently been invaded by many exotic ant species7. Geometridae) in the Hawaiian Islands, Ph.D. The invasion of native vegetation by exotic ants has Dissertation, University of Hawaii (1984). reduced the abundance of endemic arthropods8. For 5. Henneman, M. L. and Memmott, J. Science 293, example, the invasive ants Linepithema humile (Mayr), 1314–1316 (2001). Anoplolepis gracilipes (F. Smith), and P. megacephala 6. Wetterer, J. K. Pacific Science 61, 4437-456 (2007) have gradually been invading native forests where 7. Krushelnycky, P. D., Loope, L. L. and Reimer, N. J. Eupithecia caterpillars are found. Although it remains Proc. Entomol. Soc. 37, 1–25 (2005) unclear whether the invasive ants have reduced the 8. Cole, F. R., Medeiros, A. C., Loope, L. L. and Zuehlke, population of Eupithecia caterpillars, my simple W. W. Ecology 73, 1313–1322 (1992). experiment suggests that the invasive ant P. megacephala may affect Eupithecia caterpillars. Nature Precedings : doi:10.1038/npre.2010.5374.1 Posted 8 Dec 2010 2 .