Insect Conservation

Biological conservation typically involves either setting aside large tracts of land for "nature", or addressing and remediating specific processes that threaten large and charismatic vertebrates, such as endangered mammals and birds, or plant species or communities. The concept of conserving habitat for insects, or species thereof, seems of low priority on a threatened planet. Nevertheless, land is reserved and plans exist specifically to conserve certain insects. Such conservation efforts often are associated with human aesthetics, and many (but not all) involve the "charismatic megafauna" of entomology - the butterflies and large, showy beetles. Such charismatic insects can act as "flagship" species to enhance wider public awareness and engender financial support for conservation efforts. Single-species conservation, not necessarily of an insect, is argued to preserve many other species by default, in what is known as the "umbrella effect". Somewhat complementary to this is advocacy of a habitat-based approach, which increases the number and size of areas to conserve many insects, which are not (and arguably "do not need to be") understood on a species-by-species approach. No doubt efforts to conserve habitats of native fish globally will preserve, as a spin-off, the much more diverse aquatic insect fauna that depends also upon waters being maintained in natural condition. Equally, preservation of old-growth forests to protect tree-hole nesting birds such as owls or parrots also will conserve habitat for wood-mining insects that use timber across a complete range of wood species and states of decomposition. Habitat-based conservationists accept that single-species oriented conservation is important but argue that it may be of limited value for insects because there are so many species. Furthermore, rarity of insect species may be due to populations being localized in just one or a few places, or in contrast, widely dispersed but with low density over a wide area. Clearly, different conservation strategies are required for each case.

Migratory species, such as the monarch butterfly (Danaus plexippus), require special conservation. Mon-archs from east of the Rockies overwinter in Mexico and migrate northwards as far as Canada throughout the summer (section 6.7). Critical to the conservation of these monarchs is the safeguarding of the overwintering habitat at Sierra Chincua in Mexico. A most significant insect conservation measure implemented in recent years is the decision of the Mexican government to support the Monarch Butterfly Biosphere Reserve established to protect the phenomenon. Although the monarch butterfly is an excellent flagship insect, the preservation of western overwintering populations in coastal California (see Plate 3.5) protects no other native species. The reason for this is that the major resting sites are in groves of large introduced eucalypt trees, especially blue gums, which are faunist-ically depauperate in their non-native habitat.

A successful example of single-species conservation involves the El Segundo blue, Euphilotes battoides ssp. allyni, whose principal colony in sand dunes near Los Angeles airport was threatened by urban sprawl and golf course development. Protracted negotiations with many interests resulted in designation of 80 hectares as a reserve, sympathetic management of the golf course "rough" for the larval food plant Erigonum parvifolium (buckwheat), and control of alien plants plus limitation on human disturbance. Southern Californian coastal dune systems are seriously endangered habitats, and management of this reserve for the El Segundo blue conserves other threatened species.

Land conservation for butterflies is not an indulgence of affluent southern Californians: the world's largest butterfly, the Queen Alexandra's birdwing (Ornithoptera alexandrae), of Papua New Guinea (PNG) is a success story from the developing world. This spectacular species, whose caterpillars feed only on Aristolochia dielsiana vines, is limited to a small area of lowland rainforest in northern PNG and has been listed as endangered. Under PNG law, this birdwing species has been protected since 1966, and international commercial trade was banned by listing on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Dead specimens in good condition command a high price, which can be more than US$2000. In 19 78, the PNG governmental Insect Farming and Trading Agency (IFTA), in Bulolo, Morobe Province, was established to control conservation and exploitation and act as a clearinghouse for trade in Queen Alexandra's birdwings and other valuable butterflies. Local cultivators, numbering some 450 village farmers associated with IFTA, "ranch" their butterflies. In contrast to the Kenyan system described in section 1.5, farmers plant appropriate host vines, often on land already cleared for vegetable gardens at the forest edge, thereby providing food plants for a chosen local species of butterfly. Wild adult butterflies emerge from the forest to feed and lay their eggs; hatched larvae feed on the vines until pupation when they are collected and protected in hatching cages. According to species, the purpose for which they are being raised, and conservation legislation, butterflies can be exported live as pupae, or dead as high-quality collector specimens. IFTA, a non-profit organization, sells some $400,000 worth of PNG insects yearly to collectors, scientists, and artists around the world, generating an income for a society that struggles for cash. As in Kenya, local people recognize the importance of maintaining intact forests as the source of the parental wild-flying butterflies of their ranched stock. In this system, the Queen Alexandra's birdwing butterfly has acted as a flagship species for conservation in PNG and the success story attracts external funding for surveys and reserve establishment. In addition, conserving PNG forests for this and related birdwings undoubtedly results in conservation of much diversity under the umbrella effect.

The Kenyan and New Guinean insect conservation efforts have a commercial incentive, providing impoverished people with some recompense for protecting natural environments. Commerce need not be the sole motivation: the aesthetic appeal of having native birdwing butterflies flying wild in local neighborhoods, combined with local education programs in schools and communities, has saved the subtropical Australian Richmond birdwing butterfly (Troides or Ornithoptera richmondia) (see Plate 2.2). Larval Richmond birdwings eat Pararistolochia or Aristolochia vines, choosing from three native species to complete their development. However, much coastal rainforest habitat supporting native vines has been lost, and the alien South American Aristolochia elegans ("Dutchman's pipe"), introduced as an ornamental plant and escaped from gardens, has been luring females to lay eggs on it as a prospective host. This oviposition mistake is deadly since toxins of this plant kill young caterpillars. The answer to this conservation problem has been an education program to encourage the removal of Dutchman's pipe vines from native vegetation, from sale in nurseries, and from gardens and yards. Replacement with native Pararistolochia was encouraged after a massive effort to propagate the vines. Community action throughout the native range of the Richmond birdwing appears to have reversed its decline, without any requirement to designate land as a reserve.

Evidently, butterflies are flagships for invertebrate conservation - they are familiar insects with a non-threatening lifestyle. However, certain orthopterans, including New Zealand wetas, have been afforded protection, and we are aware also of conservation plans for dragonflies and other freshwater insects in the context of conservation and management of aquatic environments, and of plans for firefly (beetle) and glow worm (fungus gnat) habitats. Agencies in certain countries have recognized the importance of retention of fallen dead wood as insect habitat, particularly for long-lived wood-feeding beetles.

Designation of reserves for conservation, seen by some as the answer to threat, rarely is successful without understanding species requirements and responses to management. The butterfly family Lycaenidae (blues, coppers, and hairstreaks) includes perhaps 50% of the butterfly diversity of some 6000 species. Many have relationships with ants (myrmecophily; see section 12.3), some being obliged to pass some or all of their immature development inside ant nests, others are tended on their preferred host plant by ants, yet others are predators on ants and scale insects, while tended by ants. These relationships can be very complex, and may be rather easily disrupted by environmental changes, leading to endangerment of the butterfly. Certainly in western Europe, species of Lycaenidae figure prominently on lists of threatened insect taxa. Notoriously, the decline of the large blue butterfly Maculinea arion in England was blamed upon over-collection and certainly some species have been sought after by collectors (but see Box 1.1). Action plans in Europe for the reintroduction of this and related species and appropriate conservation management of other Maculinea species have been put in place: these depend vitally upon a species-based approach. Only with understanding of general and specific ecological requirements of conservation targets can appropriate management of habitat be implemented.

Box 1.1 Collected to extinction?

The large blue butterfly (Maculinea arion) was reported to be in serious decline in southern England in the late 19th century, a phenomenon ascribed then to poor weather. By the mid-20th century this attractive species was restricted to some 30 colonies in south-western England. Only one or two colonies remained by 1974 and the estimated adult population had declined from about 100,000 in 1950 to 250 in some 20 years. Final extinction of the species in England in 1979 followed two successive hot, dry breeding seasons. Since the butterfly is beautiful and sought by collectors, excessive collecting was presumed to have caused at least the long-term decline that made the species vulnerable to deteriorating climate. This decline occurred even though a reserve was established in the 1930s to exclude both collectors and domestic livestock in an attempt to protect the butterfly and its habitat.

Evidently, habitat had changed through time, including a reduction of wild thyme (Thymus praecox), which provides the food for early instars of the large blue's caterpillar. Shrubbier vegetation replaced short-turf grassland because of loss of grazing rabbits (through disease) and exclusion of grazing cattle and sheep from the reserved habitat. Thyme survived, however, but the butterflies continued to decline to extinction in Britain.

A more complex story has been revealed by research associated with reintroduction of the large blue to England from continental Europe. The larva of the large blue butterfly in England and on the European continent is an obligate predator in colonies of red ants belonging to species of Myrmica. Larval large blues must enter a Myrmica nest, in which they feed on larval ants. Similar predatory behavior, and/or tricking ants into feeding them as if they were the ants' own brood, are features

Tramp ants and biodiversity 17

in the natural history of many Lycaenidae (blues and coppers) worldwide (see p. 15). After hatching from an egg laid on the larval food plant, the large blue's caterpillar feeds on thyme flowers until the molt into the final (fourth) larval instar, around August. At dusk, the caterpillar drops to the ground from the natal plant, where it waits inert until a Myrmica ant finds it. The worker ant attends the larva for an extended period, perhaps more than an hour, during which it feeds from a sugar gift secreted from the caterpillar's dorsal nectary organ. At some stage the caterpillar becomes turgid and adopts a posture that seems to convince the tending ant that it is dealing with an escaped ant brood, and it is carried into the nest. Until this stage, immature growth has been modest, but in the ant nest the caterpillar becomes predatory on ant brood and grows for 9 months until it pupates in early summer of the following year. The caterpillar requires an average 230 immature ants for successful pupation. The adult butterfly emerges from the pupal cuticle in summer and departs rapidly from the nest before the ants identify it as an intruder.

Adoption and incorporation into the ant colony turns out to be the critical stage in the life history. The complex system involves the "correct" ant, Myrmica sabuleti, being present, and this in turn depends on the appropriate microclimate associated with short-turf grassland. Longer grass causes cooler near-soil microclimate favoring other Myrmica species, including M. scabrinodes that may displace M. sabuleti. Although caterpillars associate apparently indiscriminately with any Myrmica species, survivorship differs dramatically:

with M. sabuleti approximately 15% survive, but an unsustainable reduction to <2% survivorship occurs with M. scabrinodes. Successful maintenance of large blue populations requires that >50% of the adoption by ants must be by M. sabuleti.

Other factors affecting survivorship include the requirements for the ant colony to have no alate (winged) queens and at least 400 well-fed workers to provide enough larvae for the caterpillar's feeding needs, and to lie within 2 m of the host thyme plant. Such nests are associated with newly burnt grasslands, which are rapidly colonized by M. sabuleti. Nests should not be so old as to have developed more than the founding queen: the problem here being that the caterpillar becomes imbued with the chemical odors of queen larvae while feeding and, with numerous alate queens in the nest, can be mistaken for a queen and attacked and eaten by nurse ants.

Now that we understand the intricacies of the relationship, we can see that the well-meaning creation of reserves that lacked rabbits and excluded other grazers created vegetational and microhabitat changes that altered the dominance of ant species, to the detriment of the butterfly's complex relationships. Over-collecting is not implicated, although climate change on a broader scale must play a role. Now five populations originating from Sweden have been reintroduced to habitat and conditions appropriate for M. sabuleti, thus leading to thriving populations of the large blue butterfly. Interestingly, other rare species of insects in the same habitat have responded positively to this informed management, suggesting an umbrella role for the butterfly species.

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