Defense in insects

'' Walking sticks (order Phasmatodea), many katydid species (family Tettigoniidae), and moths (order Lepidoptera) are just a few of the insects that have evolved specialized camouflage. This allows them to hide within their environment because of a resemblance to the general background or an inedible object. Cost and benefit perspective Butterflies (order Lepidoptera) are a good example of the balancing act between the costs and benefits associated with defense. In order to take off, butterflies must have a thorax temperature of . This energy is derived both internally through muscles and externally through picking up solar radiation through the body or wings. When looked at in this light, cryptic coloration to escape from predators, markings to attract conspecifics or warn predators (aposematism), and the absence of color to absorb adequate solar radiation, all play key roles in survival. Only when these three affairs are in balance does the butterfly maximize its fitness. ==Mimicry==

Mimicry is a form of defense which describes when a species resembles another recognized by natural enemies, giving it protection against predators. Mimicry is divided into two parts, Batesian mimicry and Müllerian mimicry. Batesian mimicry In Batesian mimicry, an aposematic inedible model has an edible mimic. Automimics are individuals that, due to environmental conditions, lack the distasteful or harmful chemicals of conspecifics, but are still indirectly protected through their visibly identical relatives. An example can be found in the plain tiger (Danaus chrysippus), a non-edible butterfly, which is mimicked by multiple species, the most similar being the female danaid eggfly (Hypolimnas misippus). Müllerian mimicry In Müllerian mimicry, a group of species benefit from each other's existence because they all are warningly colored in the same manner and are distasteful. The best examples of this phenomenon can be found within the butterfly genus Heliconius. ==Behavioral responses==

that might attract predators or parasites. Behavioral responses to escape predation include burrowing into substrate and being active only through part of the day. Furthermore, insects may feign death, a response termed thanatosis. Beetles, particularly weevils, do this frequently. Bright colors may also be flashed underneath cryptic ones. A startle display occurs when prey takes advantage of these markings after being discovered by a predator. The striking color pattern, which often includes eyespots, is intended to evoke prompt enemy retreat. Better formed eyespots seem to result in better deterrence. ==Mechanical defenses==

Insects have had millions of years to evolve mechanical defenses. Perhaps the most obvious is the cuticle. Although its main role lies in support and muscle attachment, when extensively hardened by the cross-linking of proteins and chitin, or sclerotized, the cuticle acts as a first line of defense. Additional physical defenses include modified mandibles, horns, and spines on the tibia and femur. When these spines take on a main predatory role, they are termed raptorial. Some insects uniquely create retreats that appear uninteresting or inedible to predators. ==Autotomy==

Autotomy, or the shedding of appendages, Harvestmen (order Opiliones) also use autotomy as a first line of defense against predators. ==Chemical defenses==

wraps up a large milkweed bug and subsequently cuts it from its web. This illustrates the protection the bug gained form feeding on milkweed. Unlike pheromones, allomones, defensive chemicals, harm the receiver at the benefit of the producer. In the insect realm, chemical defenses are quite unevenly distributed. There is great variation in the presence and absence of chemical arms among orders and families to even within families. Many compounds are derived from the main food source of insect larvae, and occasionally adults, feed, whereas other insects are able to synthesize their own toxins. Class II chemicals are essentially harmless. They stimulate scent and taste receptors so as to discourage feeding. They are volatile and reactive, including acids, aldehydes, aromatic ketones, quinones, and terpenes. Furthermore, they may be aposematic, indicating through odors the presence of chemical defenses. Insects may use combinations of the two. Pasteels, Grégoire, and Rowell-Rahier grouped chemical defenses into three types: compounds that are truly poisonous, those that restrict movement, and those that repel predators. True poisons, essentially Class I compounds, interfere with specific physiological processes or act at certain sites. Repellents irritate the chemical sensitivity of predators. Impairment of movement and sense organs is achieved through sticky, slimy, or entangling secretions that act mechanically rather than chemically. This last grouping of chemicals has both Class I and Class II properties. Some chemicals can have multiple effects. ==Collective defenses in social insects==

Many chemically defended insect species take advantage of clustering over solitary confinement. Termites (order Isoptera), like eusocial ants, wasps, and bees, rely on a caste system to protect their nests. The evolution of fortress defense is closely linked to the specialization of soldier mandibles. Soldiers can have biting-crushing, biting-cutting, cutting, symmetrical snapping, and asymmetrical snapping mandibles. These mandibles may be paired with frontal gland secretion, although snapping soldiers rarely utilize chemical defenses. The Trigona fuscipennis species in particular, make use of attraction, landing, buzzing and angular flights as typical alarm behaviors. But biting is the prominent form of defense among T. fuscipennis bees and involve their strong, sharp five-toothed mandibles. T. fuscipennis bees have been discovered to engage in suicidal biting in order to defend the nest and against predators. Humans standing in the vicinity of nests are almost always attacked and experience painful bites. The Trigona workers give a painful and persistent bite, are difficult to remove, and usually die during the attack. Closer to the nest, it causes social insects to aggregate and may subsequently produce an attack against the threat. The Polistes canadensis, a primitively eusocial wasp, will emit a chemical alarm substance at the approach of a predator, which will lower their nestmates' thresholds for attack, and even attract more nestmates to the alarm. The colony is thus able to rise quickly with its sting chambers open to defend its nest against predators. In nonsocial insects, these compounds typically stimulate dispersal regardless of location. Chemical alarm systems are best developed in aphids and treehoppers (family Membracidae) among the nonsocial groups. Alarm pheromones take on a variety of compositions, ranging from terpenoids in aphids and termites to acetates, an alcohol, and a ketone in honey bees to formic acid and terpenoids in ants. ==Immunity==

Insects, like nearly every other organism, are subject to infectious diseases caused by viruses, bacteria, fungi, protozoa, and nematodes. ==Role of phenotypic plasticity==

Phenotypic plasticity is the capacity of a single genotype to exhibit a range of phenotypes in response to variation in the environment. For example, in Nemoria arizonaria caterpillars, the cryptic pattern changes according to season and is triggered by dietary cues. In the spring, the first brood of caterpillars resembles oak catkins, or flowers. By the summer when the catkins have fallen, the caterpillars discreetly mimic oak twigs. No intermediate forms are present in this species, although other members of the genus Nemoria, such as N. darwiniata, do exhibit transitional forms. ==See also==