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Plate 6

6.1 The cryptic adult moths of four species of Acronicta (Lepidoptera: Noctuidae): A. alni, the alder moth (top left); A. leporina, the miller (top right); A. aceris, the sycamore (bottom left); and A. psi, the grey dagger (bottom right) (D. Carter and R.I. Vane-Wright).

6.2 Aposematic or mechanically protected caterpillars of the same four species of Acronicta: A. alni (top left); A. leporina (top right); A. aceris (bottom left); and A. psi (bottom right); showing the divergent appearance of the larvae compared with their drab adults (D. Carter and R.I. Vane-Wright).

6.3 A blister beetle, Lyttapolita (Coleoptera: Meloidae), reflex-bleeding from the knee joints; the hemolymph contains the toxin cantharidin (sections 14.4.3 & 15.2.2) (T. Eisner).

6.4 One of Bates' mimicry complexes from the Amazon Basin involving species from three different lepidopteran families

- Methona confusa confusa (Nymphalidae: Ithomiinae) (top), Lycorea ilione ilione (Nymphalidae: Danainae) (second from top), Patia orise orise (Pieridae) (second from bottom), and a day-flying moth of Gazera heliconioides (Castniidae) (R.I. Vane-Wright).

6.5 An aposematic beetle of the genus Lycus (Coleoptera: Lycidae) on the flower spike of Cussonia (Araliaceae) from South Africa (P.J. Gullan).

6.6 A mature cottony-cushion scale, Iceryapurchasi (Hemiptera: Margarodidae), with a fully formed ovisac, on the stem of a native host plant from Australia (P.J. Gullan).

6.7 Adult male gypsy moth, Lymantria dispar (Lepidoptera: Lymantriidae), from New Jersey, USA (D.C.F. Rentz).

figure prominently on lists of threatened insect taxa. Notoriously, the decline of the large blue butterfly Phengaris (formerly Maculinea) arion in England was blamed upon overcollection (but see Box 1.1). Action plans in Europe for the reintroduction of this and related species and appropriate conservation management of Phengaris 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.

We conclude with a review of the conservation of insects, with examples, including text boxes on the conservation of the large blue butterfly in England (Box 1.1), the effects of tramp ants on biodiversity (Box 1.2), and the issue of sustainable human use of mopane "worms", the caterpillars of African emperor moths (Box 1.3).

Box 1.1 Collected to extinction?

The large blue butterfly, Phengaris (formerly Maculinea) arion (Lepidoptera: Lycaenidae), 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 southwestern 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 in the natural history of many Lycaenidae (blues and coppers) worldwide (see sections 1.8 and 12.3). 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 9-10 months until it pupates in early summer of the following year. The caterpillar requires an average 230 immature ants for successful pupation. It apparently escapes predation by the ants by secreting surface chemicals that mimic those of the ant brood, and probably receives special treatment in the colony by producing sounds that mimic those of the queen ant (section 12.3). 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 Myrmica 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 less than 2% survivorship occurs with M. scabrinodes. Successful maintenance of large blue populations requires that more than 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 with numerous alate queens in the nest the caterpillar 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 vegetation 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.

Box 1.2 Tramp ants and biodiversity

No ants are native to Hawai'i yet there are more than 40 species on the island: all have been brought from elsewhere within the last century. In fact all social insects (honey bees, yellowjackets, paper wasps, termites, and ants) on Hawai'i arrived with human commerce. Almost 150 species of ants have hitchhiked with us on our global travels and managed to establish themselves outside their native ranges. The invaders of Hawai'i belong to the same suite of ants that have invaded the rest of the world, or seem likely to do so in the near future. From a conservation perspective one particular behavioral subset is very important, the so-called invasive tramp ants. They rank amongst the world's most serious pest species, and local, national, and international agencies are concerned with their surveillance and control. The big-headed ant (Pheidole megacephala), the long-legged or yellow crazy ant (Anoplolepis gracilipes), the Argentine ant (Linepithema humile), the "electric" or little fire ant (Wasmannia auro-punctata), and tropical fire ants (Solenopsis species) are considered the most serious of these ant pests.

Invasive ant behavior threatens biodiversity, especially on islands such as Hawai'i, the Galapagos, and other Pacific Islands (see section 8.7). Interactions with other insects include the protection and tending of aphids and scale insects for their carbohydrate-rich honeydew secretions. This boosts densities of these insects, which include invasive agricultural pests. Interactions with other arthropods are predominantly negative, resulting in aggressive displacement and/or predation on other species, even other tramp ant species encountered. Initial founding is often associated with unstable environments, including those created by human activity. The tendency for tramp ants to be small and shortlived is compensated by year-round increase and rapid production of new queens. Nestmate queens show no hostility to each other. Colonies reproduce by the mated queen and workers relocating only a short distance from the original nest, a process known as budding. When combined with the absence of intraspecific antagonism between newly founded and natal nests, colony budding ensures the gradual spreading of a "supercolony" across the ground.

Although initial nest foundation is associated with human- or naturally disturbed environments, most invasive tramp species can move into more natural habitats and displace the native biota. Ground-dwelling insects, including many native ants, do not survive the encroachment, and arboreal species may follow into local extinction. Surviving insect communities tend to be skewed towards subterranean species and those with especially thick cuticle such as carabid beetles and cockroaches, which also are chemically defended. Such an impact can be seen from the effects of big-headed ants during the monitoring of rehabilitated sand mining sites, using ants as indicators (section 9.7). Six years into rehabilitation, as seen in the graph (from Majer 1985), ant diversity neared that found in un-impacted control sites, but the arrival of P. megacephala dramatically restructured the system, seriously reducing diversity relative to controls. Even large animals can be threatened by ants: land crabs on Christmas Island, horned lizards in southern California, hatchling turtles in south-eastern USA, and ground-nesting birds everywhere. Invasion by Argentine ants of fynbos, a mega-diverse South African plant assemblage, eliminates ants that specialize in carrying and burying large seeds, but not those that carry smaller seeds (see

section 11.3.2). Since the vegetation originates by germination after periodic fires, the shortage of buried large seeds is predicted to cause dramatic change to vegetation structure.

Introduced ants are very difficult to eradicate: all attempts to eliminate fire ants in the USA have failed. In contrast, it is hoped that an ongoing campaign, costing nearly A$200 million (more than US$150 million) in the first 8 years, may prevent Solenopsis invicta from establishing as an "invasive" species in Australia. The first fire ant sites were found around Brisbane in February 2001, although this ant is suspected to have been present for a number of years prior to its detection. At the height of surveillance, the area infested by fire ants extended to some 80,000 ha. Potential economic damage in excess of A$100 billion over 30 years was estimated if control failed, with inestimable damage to native biodiversity continent-wide. Although intensive searching, baiting, and destruction of nests appear to have been successful in eliminating major infestations, all nests must be eradicated to prevent resurgence, and thus continual monitoring and containment measures are essential. Undoubtedly the best strategy for control of invasive ants is quarantine diligence to prevent their entry, and public awareness to detect accidental entry.

Box 1.3 Sustainable use of mopane worms

An important economic insect in Africa is the larva (caterpillar) of emperor moths, especially Imbrasia belina (illustrated here as the adult moth and a late-instar larva feeding on mopane, after photographs by R. Oberprieler). Mature larvae are harvested for food across much of southern Africa, including Angola, Namibia, Zimbabwe, Botswana, and Northern Province of South Africa. The distribution coincides with that of mopane (Colophospermum mopane) (shown in the map, adapted from van Voorthuizen 1976), a leguminous tree which is the preferred host plant of the caterpillar and dominates the "mopane woodland" landscape.

Early-instar larvae are gregarious and forage in aggregations of up to 200 individuals: individual trees may be defoliated by large numbers of caterpillars, but regain their foliage if seasonal rains are timely. Throughout their range, and especially during the first larval flush in December, mopane worms are a valued protein source to frequently protein-deprived rural populations. A second cohort may appear some 3-4 months later if conditions for mopane trees are suitable. It is the final-instar larva that is harvested, usually by shaking the tree or by direct collecting from foliage. Preparation is by degutting and drying, and the product may be canned and stored, or transported for sale to a developing gastronomic market in South African towns. Harvesting mopane produces a cash input into rural economies: a calculation in

the mid-1990s suggested that a month of harvesting mopane generated the equivalent to the remainder of the year's income to a South African laborer. Not surprisingly, large-scale organized harvesting has entered the scene accompanied by claims of reduction in harvest through unsustainable over-collection. Closure of at least one canning plant was blamed on shortfall of mopane worms.

Decline in the abundance of caterpillars is said to result from both increasing exploitation and reduction in mopane woodlands. In parts of Botswana, heavy commercial harvesting is claimed to have reduced moth numbers. Threats to mopane worm abundance include deforestation of mopane woodland and felling or branch-lopping to enable caterpillars in the canopy to be brought within reach. Inaccessible parts of the tallest trees, where mopane worm density may be highest, undoubtedly act as refuges from harvest and provide the breeding stock for the next season, but mopane trees are felled for their mopane crop. However, since mopane trees dominate huge areas - for example, over 80% of the trees in Etosha National Park are mopane - the trees themselves are not endangered.

The problem with blaming the more intensive harvesting for reduction in yield for local people is that the species is patchy in distribution and highly eruptive. The years of reduced mopane harvest seem to be associated with climate-induced drought (the El NiƱo effect) throughout much of the mopane woodlands. Even in the northernmost part of South Africa, long considered to be over-harvested, the resumption of seasonal, drought-breaking rains can induce large mopane worm outbreaks. This is not to deny the importance of research into potential over-harvesting of mopane, but evidently further study and careful data interpretation are needed.

Research already undertaken has provided some fascinating insights. Mopane woodlands are prime elephant habitat, and by all understanding these megaherbivores that uproot and feed on complete mopane trees are keystone species in this system. However, calculations of the impact of mopane worms as herbivores showed that in their 6-week larval cycle the caterpillars could consume 10 times more mopane leaf material per unit area than could elephants over 12 months. Furthermore, in the same period 3.8 times more fecal matter is produced by mopane worms than by elephants.

Notoriously, elephants damage trees, but this benefits certain insects: the heartwood of a damaged tree is exposed as food for termites providing eventually a living but hollow tree. Native bees use the resin that flows from elephant-damaged bark for their nests. Ants nest in these hollow trees and may protect the tree from herbivores, both animal and mopane worm. Elephant populations and mopane worm outbreaks vary in space and time, depending on many interacting biotic and abiotic factors, of which harvest by humans is but one.

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