Adult Behavior

Males usually begin emergence and peak in numbers a few days ahead of females. Both are sexually mature upon eclosion, and males of nearly all moths are attracted by chemical signals (pheromones) emitted by "calling" females. Hence, in most Lepidoptera mating takes place soon after female eclosion, and she has mature eggs ready to be fertilized and deposited within the first 24 h. Mate-seeking involves primarily visual cues in most butterflies, although there may be short-range pheromones produced by one or both sexes that mitigate courtship. Males, and females too in most species, mate more than once. It is assumed that sperm precedence prevails, wherein the most recent male's sperm is effective.

Adults of both sexes of most Lepidoptera feed and in confinement die quickly if water is not available. Feeding on honey-enriched fluids extends the life of some moths and increases fecundity. Most macromoths and butterflies feed at flowers, imbibing nectar, whereas most micromoths do not and apparently gain nourishment from extrafloral nectaries, sap flows, and honeydew secreted by aphids or other Homoptera. Exceptions occur in diurnal microlepidoptera (e.g., Adelidae, Sesiidae, Heliodinidae, Scythrididae, Plutellidae, and Tortricidae, but not nocturnal species of the latter three families), which visit flowers, often other than the larval hosts. The mouthparts are nonfunctional in a few families (e.g., Lasiocampidae, Lymantriidae) and in specialized species such as winter-active Geometridae and Ethmiidae, and females possess mature eggs upon eclosion.

Host-plant selection is made primarily by the female, which seeks by chemical and tactile cues the proper substrate or habitat for oviposition. This choice is made by instinct, inherited genetically, and the newly hatched larvae also require specific stimuli, detected by chemoreceptors on the antennae and mouthparts; in host-specific species, they starve if the proper plant is not available, ignoring plants or synthetic diets that are quite acceptable and sufficient for nourishment of generalist species.

Most butterflies and moths live only a few days, until mating and egg laying are accomplished, but some are active for several weeks, or they may overwinter as adults and become active on warm days. Some adult microlepidoptera enter a prereproductive state lasting through summer and winter, followed by mating and oviposition in early spring.

Larval Development

The newly formed larva, or caterpillar, first bites its way out of the eggshell, leaving a crescentic slit or ragged hole at the micropylar end. Some species then eat the reminder of the eggshell. All growth takes place during the larval stages, so caterpillars consume enough nutrients to carry through cocoon formation, pupation, and metamorphosis to the adult. It must be sufficient for the moth or butterfly to move to its first feeding or, in species with nonfeeding adults, enough to provide for complete egg development of the next generation. To accommodate growth, the larva molts its skin (cuticle) several times, through successively larger stages (instars). Most Lepidoptera undergo five or six instars, but many larvae that feed on detritus or dry plant material undergo indeterminate numbers of instars.

Silk is produced by paired labial glands. It is composed of two proteins secreted in a viscous fluid in two strands, which consolidate as they leave the spinneret and contact the air. Its functions are many: first instars of many species are dispersed by air currents on silk strands; many or most species lay down a silk line as they move, enabling them to cling to substrates; silk is used by most external-feeding micromoths to form shelters in foliage or other food sources, and some construct portable cases from which they feed; others line tunnels with silk in fruits, stems, roots, or soil from which they forage to feed. Finally, silk is used in cocoon formation

FIGURES 17-22 Leaf mines. (17) Stigmella variella (Nepticulidae) on Quercus agrifolia; (18) mature larvae of Coptodisca arbutiella (Heliozelidae, Incurvarioidea) and their abandoned mines, on Arctostaphylos; (19) Cameraria gaultheriella (Gracillariidae) on Gaultheria shallon; (20) Marmara arbutiella (Gracillariidae) on Arbutus menziesii; (21) Phyllocnistis populiella (Phyllocnistidae, Gracillarioidea) on Populus tremuloides; (22) Epinotia nigralbana (Tortricidae) on Arctostaphylos (photographs by J. Powell, all California, except Fig. 21, Alaska).

FIGURES 17-22 Leaf mines. (17) Stigmella variella (Nepticulidae) on Quercus agrifolia; (18) mature larvae of Coptodisca arbutiella (Heliozelidae, Incurvarioidea) and their abandoned mines, on Arctostaphylos; (19) Cameraria gaultheriella (Gracillariidae) on Gaultheria shallon; (20) Marmara arbutiella (Gracillariidae) on Arbutus menziesii; (21) Phyllocnistis populiella (Phyllocnistidae, Gracillarioidea) on Populus tremuloides; (22) Epinotia nigralbana (Tortricidae) on Arctostaphylos (photographs by J. Powell, all California, except Fig. 21, Alaska).

preceding pupation, within the larval shelter or gallery or separately, sometimes as a characteristically shaped structure.

Larval habits vary widely and often are quite specific for a family, genus, or species. These include leaf mining, in which a larva spends it entire life within a leaf, and the depth and form of the mines are consistent such that the moth family or genus often is recognizable from the mine (Figs. 17—22). Other types of internal feeding include stem mining; boring in seeds, stems, and roots (Figs. 25 and 26); or feeding in galls developed by plants, stimulated by the larvae (Figs. 27 and 28). Many external-feeding caterpillars avoid adverse conditions by seeking shelter in leaf litter at the base of the plant or in tunnels during the day and emerge at night to feed, when temperatures are cooler, humidity is higher, and diurnal predators are not active. Many macromoth and butterfly larvae remain exposed, motionless, protected by cryptic coloration, body form, and behavior (Figs. 29—32), or even camouflaged by a coat of flower bits or debris that collect on hooked body setae. Larvae of a few genera live gregariously in silken tents that shield them from climatic extremes (Fig. 33). Many others are protected from vertebrate predators by toxic chemicals they sequester, and advertize their presence by bright colors (aposematic) (Fig. 34).

The duration of larval development varies greatly with the feeding and life cycle types, even within families and genera. The time required to reach maturity also is dependent upon temperature within species, such as between seasonal generations. Most Lepidoptera grow slowly in early instars,

FIGURES 23-28 Case-bearers, borers, and gall inducers. (23) Thyridopteryx meadii (Psychidae, Tineoidea), case on Larrea tridentata; (24) Coleophora species (Coleophoridae, Gelechioidea) on Malus; (25) larva of Synanthedon sequoiae (Sesiidae, Sesioidea) under bark of a conifer; (26) larva of Grapholita edwardsiana (Tortricidae) in stem of Lupinus arboreus; (27) stem galls induced by Gnorimoschema baccharisella (Gelechiidae) on Baccharispilularis; (28) stem galls caused by Epiblema rudei (Tortricidae), with newly emerged moth and its pupal shell on Gutierrezia (photographs by J. Powell, except 24, 25 by R. Coville, all California).

FIGURES 23-28 Case-bearers, borers, and gall inducers. (23) Thyridopteryx meadii (Psychidae, Tineoidea), case on Larrea tridentata; (24) Coleophora species (Coleophoridae, Gelechioidea) on Malus; (25) larva of Synanthedon sequoiae (Sesiidae, Sesioidea) under bark of a conifer; (26) larva of Grapholita edwardsiana (Tortricidae) in stem of Lupinus arboreus; (27) stem galls induced by Gnorimoschema baccharisella (Gelechiidae) on Baccharispilularis; (28) stem galls caused by Epiblema rudei (Tortricidae), with newly emerged moth and its pupal shell on Gutierrezia (photographs by J. Powell, except 24, 25 by R. Coville, all California).

increasing in size much more rapidly in later instars, particularly the last. Growth after eclosion from the egg to maturity usually takes 30 to 50 days, but sometimes is more rapid, as few as 18 or 19 days. Larval life can extend much longer, particularly in species that enter quiescent phases at lower temperatures, intermittently feeding when warmer, or in detritus-feeders, which can simply wait long periods when food is not suitable. Such species may live 100 to 140 days before pupation, and those that enter obligate diapause, usually as first or last instar, typically spend 9 or 10 months as inactive larvae in addition to their feeding and growth period.

Larval Foods

The nutritional requirements of many caterpillars are generally similar. Synthetic diets that contain the same basic elements, casein, sucrose, salt, cellulose, wheat germ, amino acids, and vitamins, incorporated in an agar base, are successfully used for rearing many kinds of Lepidoptera. However, sometimes species that are specific to particular plants do not accept a synthetic diet. Hence, nutritional value alone may not be sufficient to elicit feeding, and natural plant chemicals act either as cues for feeding or as deterrents, often the same chemical in both roles with different larval species.

The majority of Lepidoptera caterpillars are phytophagous, consuming living plants, almost exclusively flowering plants,

FIGURES 29-34 Cryptic and aposematic caterpillars. (29) Oidaematophorus species (Pterophroidae) on Petasites palmatus; (30) stick-like larva of Sicya macularia (Geometridae) on Ceanothus thyrsiflorus; (31) Schizura unicornis (Notodontidae, Noctuoidea) on unidentified tree; (32) Catocala species (Noctuidae) on Quercus kelloggii; (33) tent caterpillars, Malacosoma califor-nicum (Lasiocampidae, Bombycoidea), on Quercus agrifolia; (34) Battus philenor (Papilionidae) on Aristolochia californica (photographs by J. Powell, except 31 by R. Coville, 32 by D. Wagner, all California except 31, British Columbia).

FIGURES 29-34 Cryptic and aposematic caterpillars. (29) Oidaematophorus species (Pterophroidae) on Petasites palmatus; (30) stick-like larva of Sicya macularia (Geometridae) on Ceanothus thyrsiflorus; (31) Schizura unicornis (Notodontidae, Noctuoidea) on unidentified tree; (32) Catocala species (Noctuidae) on Quercus kelloggii; (33) tent caterpillars, Malacosoma califor-nicum (Lasiocampidae, Bombycoidea), on Quercus agrifolia; (34) Battus philenor (Papilionidae) on Aristolochia californica (photographs by J. Powell, except 31 by R. Coville, 32 by D. Wagner, all California except 31, British Columbia).

and primarily angiosperms. All parts of plants are eaten, each kind of caterpillar specializing on its particular niche, leaves, flowers, fruit, stems, or roots. Some species feed internally (endophagous) as leafminers and seed or root borers, others externally (exophagous), either concealed in shelters constructed with silk or exposed. Larvae of the most primitive family, Micropterigidae, consume liverworts and mosses or are general feeders on green plants, fern sporangia, or fungal spores in moist habitats. Some other groups of moths do not feed on flowering plants (e.g., Tineidae), but specialize on wood-rot fungi (Polyporaceae) or are detritivores on the ground, under bark of dead tree limbs, or in abandoned insect and spider nests or feed on animal products in mammal burrows, bird nests, or scats, and a few can digest wool. Many species feed on fallen leaves, notably Oecophoridae and Tortricidae on Eucalyptus (Myrtaceae) in Australia, and several groups of Noctuidae in wet forest habitats. Some Lepidoptera specialize on lichens (lithosiine Arctiidae, some Psychidae and Xylorictidae), mosses (some Crambidae), or ferns (unrelated species, mainly on oceanic islands). A few Lepidoptera are predaceous on scale insects or other Homoptera or in ant nests. A Hawaiian geo-metrid moth (Eupithecia) is predaceous on adult flies, which it catches by seizing the fly with elongate prolegs. Other members of the worldwide genus Eupithecia are plant feeders.

Virtually every kind of flowering plant is eaten by one or more species of caterpillar. Food preferences vary enormously among families; they are summarized in the accounts of the major families that follow. Nearly all internal feeders, such as leafminers, stem and root borers, and gall inducers, and most other microlepidoptera are specialists on one or a few related plants, whereas perhaps half or more of external-feeding macro-moth species are generalists within habitats, such as ground-dwelling cutworms feeding on low-growing herbaceous plants or shrub- and tree-feeding species. Most butterfly species are specialists.

Pupal Development

The duration of pupation during which metamorphosis to the adult occurs varies with temperature, usually requiring about 10 to 12 days, but many species require several weeks or hibernate as pupae, often for 10 months or more.

Pupal movement is an important adaptation in primitive moths and basal Ditrysia. The pupa moves forward just preceding adult eclosion and either anchors by the cremaster to silk or wedges in the emergence aperture, which is prepared by the larva to be slightly narrower than the pupal abdomen. This movement is aided by rows of dorsal, backwardly projecting spines. Gelechioidea and the Obtectomera (Figs. 1, 16B, 16C) have independently derived fusion of abdominal segments that restricts movement, enabling turning within the cocoon but not forward movement, and the adult emerges directly from the pupation site. Pupae respond to tactile stimuli, including potential predators and probing by a parasitoid wasp ovipositor, by turning or wriggling. Some moth pupae have special structures on the abdomen that produce clicking or rattling sounds when the wriggling abdomen strikes the walls of the pupal cells or parchment-like cocoon, or sounds are produced by rubbing fine pegs or rasp-like surfaces on adjacent segments. Such sounds may aid in pupal defense.

Life Cycle

Most Lepidoptera in temperate climates undergo a single annual generation (univoltine), although many have two discrete seasonal broods (bivoltine), and some produce continuous generations as long as favorable temperature conditions prevail (multivoltine). Diapause, a state of arrested development regulated by hormones, controls the life-cycle pattern and enables populations to survive during unfavorable times (winter, dry season, etc.) when necessary resources are not available. Diapause may be the single most important adaptation leading to species radiation of Lepidoptera in northern climates and high mountains, in the world's deserts and tropical dry season habitats, and in other places where insects could not grow and reproduce continuously. In Lepidoptera, diapause occurs primarily in eggs, in first or last instars, in pupae, or as a reproductive delay in adults, depending on the species. In Mediterranean climates, larval feeding typically occurs in spring when foliation peaks, and diapause lasts through the dry season in summer and hibernation in winter. Some species aestivate in diapause as prepupal larvae or pupae, fly in autumn, and then hibernate as adults or eggs. Multivoltine species enter diapause at the end of the growing season, often triggered by decreasing day length, or the larvae simply wait in a quiescent state, feeding slowly on warm days through winter, and metamorphose, and adults eclose with warmer temperature in spring.

Most tropical Lepidoptera are too poorly documented to estimate the proportion of multivoltine to other life-cycle patterns. Some species migrate from wet regions to dry forest habitats at the beginning of the rainy season to take advantage of the newly available resources, but others undergo diapause through the dry season.

Many Lepidoptera are capable of maintaining the diapause to a second or later season if appropriate climatic conditions do not occur. This happens as a regular phenomenon in species adapted to seed feeding on plants with biennial crops such as conifers or sporadically in species that depend upon resources that are limited to a specific season but are erratic in abundance, such as flowering and fruiting by desert plants. Numerous pre-pupal larvae of yucca moths (Prodoxidae) have metamorphosed synchronously after 8 to 30 years in diapause under experimental conditions.

Was this article helpful?

0 0
Bee Keeping

Bee Keeping

Make money with honey How to be a Beekeeper. Beekeeping can be a fascinating hobby or you can turn it into a lucrative business. The choice is yours. You need to know some basics to help you get started. The equipment needed to be a beekeeper. Where can you find the equipment you need? The best location for the hives. You can't just put bees in any spot. What needs to be considered when picking the location for your bees?

Get My Free Ebook


Post a comment