Can Hawaiian carnivorous caterpillars attack invasive ants or vice versa?
Shinji Sugiura1,2
1
Nature Precedings : doi:10.1038/npre.2010.5374.1 : Posted 8 Dec 2010
Department of Forest Entomology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba,
Ibaraki 305-8687, Japan
2
Center 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
unique habits, such as ambush predating in caterpillars1
and ground-dwelling in damselfly nymphs2, because the
islands are isolated and originally lacked predators, such
as ants and wasps3. However, many exotic species have
been introduced to the islands through human activities,
which has affected the native fauna3.
Ambush carnivorous caterpillars (Eupithecia spp.;
Lepidoptera: Geometridae) provide a remarkable
example of a feeding behaviour unique to the Hawaiian
Islands1,4. More than 20 endemic species of Eupithecia
have been recorded from the Hawaiian Islands1,4. While
the larvae of two Eupithecia species are herbivores, the
larvae of other species on the islands are obligate
predators1,4. The larvae of carnivorous Eupithecia perch
inconspicuously along leaf edges (Fig. 1a) and stems and
seize arthropods that touch their posterior body section1.
Their prey includes various arthropods species, such as
springtails, drosophilid flies, cockroaches, crickets,
psocids, moths, and leafhoppers1,4. Eupithecia larvae
even attack predatory arthropods. For example,
Montgomery4 reported that Eupithecia orichloris
(Meyrick) preyed on a braconid parasitoid. Although
phytophagous Eupithecia are frequently parasitised by
parasitic wasps and flies, the carnivorous species of
Eupithecia are rarely parasitised, suggesting that
carnivorous Eupithecia counterattack the parasitoids4,5.
However, spiders may defend against Eupithecia attacks;
one spider, Theridion grallator Simon, was attacked by
E. orichloris, but the spider escaped from the E.
orichloris by biting it4. Similarly, ants with strong
mandibles may counterattack Eupithecia larvae4.
However, it is unclear whether Eupithecia can attack
ants.
Here, I examined whether E. orichloris can attack ants
under laboratory conditions (21°C). An E. orichloris
larva (body length, 19.3 mm) and workers of the invasive
ant Pheidole megacephala (Fabricius) collected from
Oahu Island in early June 2010 were used for the
experiment. Pheidole megacephala has minor (body
length 2 mm) and major (3.5 mm) forms of workers;
major workers have larger heads with stronger mandibles
than minor ones6. First, I used forceps to place a minor
worker of P. megacephala on a leaf where E. orichloris
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
Nature Precedings : doi:10.1038/npre.2010.5374.1 : Posted 8 Dec 2010
perched. The E. orichloris was observed to bend the
seized the ant the instant the ant touched its posterior
body. The caterpillar seized the ant using its thoracic
(elongated spiny) legs (Fig. 1b), and then used its
mandibles to tear the ant body in two (Fig. 1c). Thus, E.
orichloris can successfully attack the minor workers of
P. megacephala. The next day, I similarly placed a major
worker of P. megacephala on a leaf where E. orichloris
perched. The E. orichloris was also observed to attack
the ant the instant the ant touched its posterior end.
However, the ant counterattacked (Fig. 1d) and was
observed to bite one of the thoracic legs of E. orichloris
(Fig. 1d) and ultimately escaped (Fig. 1e). The E.
orichloris lost a foreleg and consequently lost its ability
to seize prey (Fig. 1f). The caterpillar died 10 days later.
The Hawaiian Islands, which originally lacked ants,
have recently been invaded by many exotic ant species7.
The invasion of native vegetation by exotic ants has
reduced the abundance of endemic arthropods8. For
example, the invasive ants Linepithema humile (Mayr),
Anoplolepis gracilipes (F. Smith), and P. megacephala
have gradually been invading native forests where
Eupithecia caterpillars are found. Although it remains
unclear whether the invasive ants have reduced the
population of Eupithecia caterpillars, my simple
experiment
suggests
that
the
invasive
ant
P. megacephala may affect Eupithecia caterpillars.
ACKNOWLEDGEMENTS. I thank Vincent Costello
and Brenden Holland for providing the caterpillar. The
author was supported by a JSPS Postdoctoral Fellowship
for Research Abroad.
REFERENCES
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3. Ziegler, A. C. Hawaiian Natural History, Ecology,
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behavior,
biogeography
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