Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
80 days and begin mating 30 days after hatching. Both larvae and adult koa bugs emit odorous
defense compounds when disturbed (Johnson et al. 2005).
The koa bug has no known natural predators; however, nonnative spiders and ants are known to
parasitize C. blackburniae eggs, nymphs, and adults. The big-headed ant chews koa bug eggs and
Western yellowjacket wasps are predators of young (Johnson et al. 2005). Other species known to
kill koa bugs include Anastatus sp., Acroclisoides sp., and birds. In addition, two biocontrol agents
(Trissolcus basalis and Trichopoda pilipes) that were introduced to control the southern green stink
bug are able to locate and develop on C. blackburniae. Although these species have a relatively
minor impact on C. blackburniae overall, substantial impacts may occur at individual sites (Johnson
et al. 2005).
The koa bug has also been impacted by the reduced abundance and distribution of its host species as
a result of agricultural activities and urban development. Because these plants typically fruit at the
same time, locating host plants suitable to lay eggs may require C. blackburniae to disperse over long
distances. Studies have shown that koa bug mortality due to dispersal accounted for about 50 percent
mortality in all individuals studied (Johnson et al. 2005).
4.8.3 Cave Invertebrates
Until the 1970s, it was assumed that the young and geologically unique Hawaiian Islands did not
support an abundance of cave-adapted fauna. However, Hawaiian caves have been found to support a
diverse array of rare and highly specialized invertebrates (Howarth 1972, 1983, 1991). These
cavernicoles can be classified into three categories: (1) troglobites, which are obligate cave species;
(2) troglophyles, which can live in caves or other cave-like (moist cool dark) habitats; and (3)
trogloxenes, which can be found in caves, but do not live their entire life in caves (Howarth 1973,
1983).
The Service recognizes one species of cave invertebrate on the Island of Hawai„i, the troglobitic
cixid leafhopper Oliarus polyphemus, as a species of concern. Troglobites are only able to survive in
cave ecosystems. These species are characterized by a number of anatomical and physiological
adaptations to cave life (Barr 1968, Christiansen 1982, Holsinger 1994, Culver et al. 1995).
Troglobites tend to lose their pigmentation, eyes, and hard exoskeletons. Additionally, troglobites
have elongated appendages and sensory structures with long hairs, lengthened life span, and modified
life-history patterns. As a result of their nutrient-poor environments, the life cycle of many
troglobites is characterized by delayed reproduction, increased longevity, lower total egg production,
and production of larger eggs (Culver 1982).
Obligate cave species have narrow and specific ecological requirements. Such requirements include
high relative humidity, stable temperatures, and a preference for high CO2 levels (Howarth and Stone
1990). They do not acclimate well to rapid changes in their physical, biological, or chemical
environment (Barr 1968, Culver 1982). Troglobites also rely on energy and nutrient input from the
surface. These invertebrates primarily feed on „ōhi„a roots or other plant roots that penetrate the lava
tube roof (Howarth 1973; 1983, Howarth et al. 2007). Additional nutrient sources into caves include
plant detritus washed in by surface waters, organisms that enter caves under their own power, and
guano from bats, rats, and mice. Thus, cave systems can be strongly influenced by the surface
ecosystem (Barr 1968, Culver 1982).
4-48 Chapter 4. Refuge Biology and Habitats