Francis G. Howarth

Cavernicoles in Lava Tubes on the Island of Hawaii

Cave-adapted arthropods have evolved in lava tubes in Hawaii. This is the first report of cavernicoles from the Hawaiian islands. The specialization of the cavernicolous insects and the recent origin of the lava tubes suggest that subterranean connections between lava tubes regularly occur and provide dispersal routes. The discovery that lava tubes were colonized by representatives of the adaptively radiating native fauna offers significant potential for evolutionary studies.

Evolution in Hawaiian cave-adapted isopods (Oniscidea: Philosciidae): vicariant speciation or adaptive shifts?

We assessed evolutionary relationships among Hawaiian cave-adapted isopods using a maximum-likelihood criterion to analyze cytochrome oxidase I nucleotide sequences. Results support morphological data that two genera of philosciid isopods have invaded caves independently in the islands. In the genus Littorophiloscia, a sister relationship between a surface-dwelling species, L. hawaiiensis, and an undescribed cave species was corroborated. This evidence, along with the known parapatric distributions between species, supports a speciation event by an adaptive shift on the island of Hawaii from a marine littoral to a terrestrial subterranean habitat. The monophyletic genus Hawaiioscia contains four known obligate cave-dwelling species, each of which occurs on a separate island. However, despite present-day allopatric distributions between Hawaiioscia species, the geographic and phylogenetic patterns are not sufficient to support a vicariant mode of speciation. Instead, we believe that the known species of Hawaiioscia evolved from a widespread ancestral surface species or a group of closely related species through multiple, independent adaptive shifts on each of the islands of Kauai, Oahu, Molokai, and Maui. This is the first molecular investigation of evolutionary relationships between surface-dwelling and cavernicolous arthropods in Hawaii and it suggests that simple vicariance is insufficient to explain the evolution of troglobites in tropical zones.

Non-target Effects of Biological Control Agents

Biological control uses three strategies: management practices to enhance native agents already occurring in the system (Chapter 4); captive rearing and release of resident native agents (Chapter 3); and importation and release of non-native agents (sometimes termed ‘classical biological control’) (Chapter 2). A fourth strategy is rapidly being developed: genetic manipulation of both native and non-native agents to enhance their effectiveness against pests (see Chapter 14). An important measure of successful pest control is the effect of the control procedure on the environment, including any direct and indirect effects on non-target species. Although biological control is frequently presumed to be safe to the environment (Lai, 1988; Coulson et al., 1991; U.S. Congress, 1995; Bathon, 1996; Onstad and McManus, 1996; McEvoy, 1996; Jervis 1997), all pest control methods have inherent risks. That is, any method that reduces the population of an abundant pest organism to below an economic threshold will have community-level effects and therefore will inherently pose environmental risks. The scope of this chapter is to review the published evidence for environmental impacts of biological control on non-target organisms and to suggest ways of minimising the inherent risks. In the context of this book, non-target effects are important for they have the potential to compromise the success of biological control.

Evolutionary ecology of aeolian and subterranean habitats in Hawaii

Inhospitable lava flows, high altitude stone deserts and subterranean habitats in the Hawaiian islands are now known to support a considerable variety of endemic arthropod species. Current studies of these organisms are revealing a remarkable range of morphological, behavioral and physiological adaptations to the physically extreme environments they inhabit.

Founder effects initiated rapid species radiation in Hawaiian cave planthoppers

The Hawaiian Islands provide the venue of one of nature’s grand experiments in evolution. Here, we present morphological, behavioral, genetic, and geologic data from a young subterranean insect lineage in lava tube caves on Hawai‘i Island. The Oliarus polyphemus species complex has the potential to become a model for studying rapid speciation by stochastic events. All species in this lineage live in extremely similar environments but show strong differentiation in behavioral and morphometric characters, which are random with respect to cave age and geographic distribution. Our observation that phenotypic variability within populations decreases with increasing cave age challenges traditional views on founder effects. Furthermore, these cave populations are natural replicates that can be used to test the contradictory hypotheses. Moreover, Hawaiian cave planthoppers exhibit one of the highest speciation rates among animals and, thus, radically shift our perception on the evolutionary potential of obligate cavernicoles.

Identification of roots in lava tube caves using molecular techniques: implications for conservation of cave arthropod faunas

Lava tube cave ecosystems on the volcanic islands of Hawai‘i support communities of rare and highly specialized cave arthropods. In these cave ecosystems, plant roots, both living and dead, provide the main energy source for cave animals. Loss of deep-rooted plants over caves will affect populations of cave-adapted animals living below. Furthermore, the loss of native plant species will likely eliminate host specific cave animals. Thus, identification of plant roots currently found in caves is necessary for the development of effective management actions that encourage the growth of appropriate deep-rooted plant species, thereby protecting the underlying cave ecosystem. We used molecular techniques to identify plant roots found within cave ecosystems on the islands of Maui and Hawai‘i. Sequences of the internal transcribed spacer (ITS) regions and the 5.8S gene of nuclear ribosomal DNA from cave roots were compared to sequences of known plant species either collected on the surface over the footprint of each cave or to sequences accessioned in GenBank. Roots in the cave ecosystem studied on Maui belonged to two alien tree species: Eucalyptus tereticornis and Grevillea robusta. Within the Hawai‘i cave ecosystem, roots of two plant species were identified: the alien tree G. robusta and the native vine Cocculus orbiculatus. The Maui cave ecosystem supports populations of at least 28 species of arthropods, including eight that are blind obligate cave inhabitants. The Hawai‘i cave ecosystem supports 18 arthropod species, of which three are cave-adapted. Creating protected reserves around biologically significant caves, controlling, and preventing the introduction of harmful invasive plant species within the cave footprint, and encouraging the establishment of deep-rooted native plant species is essential for the continued survival of the unique ecosystems found within Hawaiian lava tube cave systems.

Root Communities in Lava Tubes

Plant roots are an important component of underground food webs in mesocaverns, lava tubes, and solution caves. Trees such as Metrosideros , Eucalyptus , Ficus , and Brachychiton are adapted to send their roots through porous rock to get water and nutrients. These trees are primary producers, photosynthesizing and sending energy in the form of carbohydrates into their roots. Surface species that live on and around roots may venture deep underground along roots, but most are not able to survive deep in caves and become food for predators and scavengers. In some groups, including the planthopper family Cixiidae and the moth family Noctuidae, new species have evolved traits that allow them to spend their entire life cycle underground. Besides these primary consumers (herbivores), tree root communities in caves include carnivores, detritivores, decomposers, and fungivores. Many of these animals are obligate cave species (troglobites) and are generally restricted to habitats with high humidity and low air motion found in mesocaverns and the deep cave zone. Protection of troglobites in tree root communities requires more than simply protecting the caves in which they occur, it requires determining the plant species that provide the roots, and protecting these species on the surface over the cave and associated mesocaverns.

The Old World biting midge, Forcipomyia (Lepidohelea) pulcherrima SANTOS ABREU, new to the fauna of the United States (Diptera: Ceratopogonidae)

ABSTRACT We provide the first United States records of the Old World biting midge, Forcipomyia (Lepidohelea) pulcherrima SANTOS ABREU (Diptera: Ceratopogonidae), from California, Florida and Hawaii. The fourth instar larva of F. pulcherrima is also described and illustrated for the first time.

Development of Insect Conservation in Hawai‘i

As the most isolated group of high islands in the world, the Hawaiian archipelago occupies a very special place in insect conservation: first as a cradle of evolution of a remarkable endemic fauna and second as a prime example of the vulnerability of island environments to anthropogenic changes – especially the effects of alien species. Lessons from both these themes are of global relevance, and the recognition that these same phenomena are occurring in continental systems has been important in maturing attitudes to insect conservation. Mirrored in other parts of the Pacific, such as New Zealand (Watts et al. this volume; Howarth and Ramsay 1991), external disturbances have had massive impacts on the Islands’ biota. These losses – together with the prospect of continuing severe losses – have contributed to debates over the rationale justifying alien species introductions, including non-native biological control agents. The impacts of introduced control agents are increasingly recognized as an important issue in insect conservation over the last few decades.

Chapter 38 – Cave Insects

Publisher Summary This chapter discusses the subterranean biome, highlighting terrestrial systems and the insects that are obligately adapted to live permanently in underground voids. The most conspicuous aspect displayed by obligate cave arthropods is the reduction of structures normally considered adaptive. Cave species also often lack a circadian rhythm and have relatively low metabolic and reproductive rates. A few characters are often enhanced, including modified structures such as increased hairiness, enlarged sensory organs, longer appendages, and specialized tarsi. Insects, arachnids, and millipedes are the dominant terrestrial groups living in caves. Beetles (Coleoptera), especially the families Carabidae, Leiodidae, and Staphylinidae, are well represented in the temperate caves. Troglobitic species are also found in the orders Diplura, Thysanura, Blattodea, Dermaptera, Grylloblattodea, Psocoptera, and Lepidoptera. Troglobitic bristletails (Diplura) occur mainly in temperate caves. The fantastic adaptations displayed by obligate cave animals have long intrigued biologists. Their often narrow environmental tolerances, coupled with their island-like habitats, have reinforced the view that these animals are fragile, lead an endangered existence, and are in need of conservation. Ecological studies are needed that improve our understanding of the functioning ecosystem, as well as understanding of natural successional processes. However, experimental ecological studies in caves are problematic because in few other habitats are humans so dramatically intruders as in caves.