Transcript UV fluorescing millipedes from southeastern Ohio

Ecology of Assassin Bugs (Hemiptera: Reduviidae) at the Barbara A.
Beiser Field Station
Derek Hennen
Advisor: Dr. McShaffrey
Introduction
Background
The assassin bugs (family Reduviidae) are a fascinating group of predaceous
insects. There are about 6,500 species worldwide, with 195 species present in the
United States and Canada (Hagerty & McPherson, 1999). They are considered
beneficial insects due to their dietary habits (Hagerty & McPherson, 1999) and show
usefulness for applications in biological control (Grundy et al., 2000). Assassin bugs
are generalist predators, and most use ambush tactics: they wait in place or slowly
stalk their prey before jumping upon the unfortunate victim. Once they have
captured their prey, they thrust their straw-like mouthparts into the body and inject
enzymes to kill and digest the prey before sucking out the liquefied innards.
The abundance and diversity of assassin bugs at the Barbara A. Beiser Field
Station (Figure 1) in Marietta, Ohio has only been studied informally since 2007,
when the station was established. Due to their ecological importance as predators
and lack of specific knowledge about their abundance and diversity, a field survey
was undertaken to answer questions about assassin bug ecology.
Results
Discussion
7 species of assassin bugs from four separate subfamilies were found at the field
station (Figures 2-8). Of these assassin bugs, 76.5% were found on the forested slope,
17.6% were found in the riparian forest, and 5.9% were found in old field. The
assassin bugs showed a preference for forest edge and edge of path habitats, as
predicted by the literature. Interestingly enough, 31% of the assassin bugs that were
found were spotted on one species of plant, the invasive Rosa multiflora, an import
from Asia.
The wheel bug pair fed on smaller insects than themselves, such as
Chauliognathus pensylvanicus (54 mg), but were found to take longer to kill their
prey than Mead (1974) reported, ranging from 11-24 minutes rather than “15-30
seconds.” The female laid a total of 190 eggs, and dispersal of the female after
oviposition was found to be markedly increased, with the female taking 56 flights in
32 minutes.
Purpose
Quantify assassin bug abundance and diversity at the Barbara A. Beiser Field
Station and to lay the groundwork for future insect research at the station.
Hypothesis
Assassin bugs will be most abundant in fields and marginal habitats and will not be
associated with host plants.
Figure 2. Rhiginia cruciata
Figure 3. Arilus cristatus
Figure 4. Sinea spinipes
Figure 5. Zelus luridus
Figure 6. Melanolestes picipes
Figure 7. Phymata pennsylvanica
The first hypothesis, that assassin bugs would be most abundant in fields and
marginal habitats was confirmed. The second hypothesis, that assassin bugs will not
be associated with host plants, was inconclusive. While assassin bugs were found on
a wide variety of plants (18 species), 31% were found on one plant, necessitating
more data to be collected before a conclusion can be drawn.
The assassin bugs found during the survey demonstrate the great variety in the
family. The seven species range in size from 10 mm to 38 mm, and this difference in
size in turn affects the size of prey they can catch, separating the bugs into different
ecological niches. A few species are of note for the opportunities they present for
future research. The dietary habits of Rhiginia cruciata in particular are begging to be
researched. This assassin bug is in the subfamily Ectrichodiinae, which contains
species of assassin bugs that specialize on millipedes (Carpintero & Capriles, 1996;
Dougherty, 1995). It would be very exciting to investigate whether or not R. cruciata
shows a preference for feeding on millipedes.
The discovery of the species Rocconota annulicornis at Beiser Field Station is of
note. The description by Blatchley (1926) indicates that this is an uncommon species.
It has previously only been found in four of Ohio’s counties: Harrison, Monroe,
Muskingum, and Summit (Dan Swanson, personal communication), making this the
first record of this species from Washington County. Both the nymph and adult of
this species were found (and are now in the collection at Marietta College): the
nymph on May 24th and the adult on July 21st at another site located in Little Hocking,
Washington County. The picture of the nymph may be one of the few ever
published.
The reported lethality of the wheel bug’s bite may not be as fatal for all of the
insect’s prey as has been reported. Mead (1974) does not state which insects are
killed in his reported time period, so it isn’t possible to directly compare his
observations with the ones reported here. It is likely that lethality and time until
death differs depending on the prey species. The increased flight activity in the wheel
bug after oviposition indicates that the wheel bug disperses away from the eggs after
oviposition, which would allow the female to ensure that she does not lay all of her
eggs close together—a good strategy for avoiding localized catastrophic loss of
progeny.
Literature Cited
Figure 1. Barbara A. Beiser Field Station
Figure 8. Rocconota annulicornis
(nymph)
Materials & Methods
The field station was surveyed with a variety of methods, including sweep netting
and hand picking from brush. The literature noted that forest edge habitats and field
habitats were preferred by assassin bugs (Hagerty & McPherson, 1999), and these
areas were emphasized during sampling. The survey was carried out for six weeks
between late May and mid July, with some extra sampling in mid September. Notes
were taken of plant associations, behavior, and habitat preferences of the assassin
bugs.
A breeding pair of wheel bugs, Arilus cristatus, was taken and observed in a
laboratory setting during the study. The wheel bugs were placed in a cage and fed
beetles and other insects.
Acknowledgements
I would like to thank Dr. McShaffrey, who served as my advisor, and the Marietta
College Biology Department for their support and encouragement of my research and
the Marietta College Investigative Studies Committee, which provided the funding for
this research. I would also like to thank my Capstone class for their encouragement,
and Dan Swanson for providing me with excellent information about the assassin
bugs.
Blatchley WS. 1926. Heteroptera or true bugs of eastern North America with especial
reference to the faunas of Indiana and Florida. Nature Pub. Co., Indianapolis.
1116 pp.
Carpintero DJ & Capriles JM. 1996. Diagnostic characters and key to the genera of
American Ectrichodiinae (Heteroptera, Reduviidae). Caribbean Journal of Science.
32(2): 125-141.
Dougherty V. 1995. A review of the new world Ectrichodiinae genera (Hemiptera:
Reduviidae). Transactions of the American Entomological Society (1890-). 121(4):
173-225.
Grundy PR, Maelzer DA, Bruce A, and Hassan E. 2000. A mass-rearing method for
the assassin bug Pristhesancus plagipennis (Hemiptera: Reduviidae). Biological
Control. 18: 243-250.
Hagerty AM & McPherson JE. 1999. Survey of the Reduviidae (Heteroptera) of
southern Illinois, excluding the Phymantinae, with notes on biology. The Great
Lakes Entomologist. 32(3): 133 – 160.
Mead FW. 1974. The Wheel Bug, Arilus cristatus (Linnaeus) (Hemiptera: Reduviidae).
Entomology Circular No. 143. Florida Department of Agriculture and Consumer
Services, Division of Plant Industry, Gainesville, FL.