Background

1. Ecology of Assassin Bugs (Hemiptera: Reduviidae) at the Barbara A. Beiser Field Station Derek Hennen Advisor: Dr. McShaffrey • Introduction • Results • Discussion 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. 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. 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. 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 Chauliognathuspensylvanicus(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. • Literature Cited Figure 2. Rhiginia cruciata Figure 3. Arilus cristatus Figure 4. Sinea spinipes 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 Pristhesancusplagipennis(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. • Materials & Methods • Acknowledgements 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. 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. Figure 5. Zelus luridus Figure 6. Melanolestes picipes Figure 7. Phymata pennsylvanica Figure 8. Rocconota annulicornis (nymph) Figure 1. Barbara A. Beiser Field Station