Review Sheet -- Test 3 (Week 12) Biology 1224 -- Entomology; James Adams
Interactions with other Organisms -- ECOLOGY of insects
Insect-Vertebrate Interactions --
Chap. 8, pages 199-211
This is a world of feed and be fed on. A lot of vertebrates use insects as a staple in the diet;
in turn, a lot of insects are parasitic, and occasionally predatory (dytiscids, belostomatids, odonate
naiads, large mantids, some ants), on vertebrates.
Parasites may be either ecto- or endoparasites. Parasites are often attracted by carbon
dioxide produced by potential hosts. You need to know examples of Continuous, Transitory,
and Temporary parasites. Some parasites may be flying (several Diptera, and Eye Moths!) or
crawling, some may be internal (under the skin, in the gut) during the larval stages (for example,
certain fly larvae [Bot Flies]).
Virtually all Phthiraptera and Siphonaptera, and various Dermaptera, Heteroptera,
Coleoptera, Diptera, and even a few Lepidoptera, are dependent on vertebrate blood at some
point during their development. Blood is typically ingested after a bite, accompanied by the injection
of anticoagulants. Other tissues (skin cells, sebum [oils], mucus, hairs or feathers, etc.) may be
ingested by some species.A number of hymenopteran species, particularly ants, will make
use of vertebrate tissue when available. In the process, a number of these species are also
important vectors for diseases of vertebrates. As for the aquatic insects, large vertebrates that are
mostly aquatic seem to escape parasitic attack by insects.
Vertebrate predatory effects (see below) on insects include a variety of effects on body
form and coloration for protection, and effects depend on palatability of the insects. Insects may
exhibit crypsis (camouflage of various kinds), disruptive coloration, flash coloration, mimicry
of objects (including other insects), eyespots/false head coloration, aposematic (warning) colora-
tion, and mimicry in unpalatable species (protective chemicals). In addition, species may exude
distasteful, malodorous secretions, make sounds, and have other special behaviors to deter predators.
Check out the COLOR PLATES (after page 338 in your textbook).
Cryptic coloration and behavior includes remaining immobile on an appropriate back-
ground and using camouflage against background, special resemblance (twigs, flowers, bird
droppings), shadow elimination (fringes, checkering, etc.), disruptive coloration. Escape
behavior in these species is usually by dropping, jumping, or erratic flight. They may also use
eyespots/false head coloration. There are also examples of insects whose forewings are muted,
hiding brightly colored hindwings that are rapidly flashed when the insect is detected -- this is
thought to startle the vertebrate predator temporarily and allow escape. Batesian mimicry of
nasty insects (called models) is also common (sometimes limited to just females -- sex-limited
mimicry), and some species may produce mimetic sounds of unpalatable species.
A number are brightly colored -- this may represent aposematic (warning) coloration, and
some have additional aposematic behaviors, including behaviors that show off bright colors, or
sounds that indicate nasty taste in nighttime active insects (Tiger Moths). Mullerian mimicry
may also be exhibited by unpalatable species, as well as aggregation behavior (presents a bigger
signal). In addition, species may exude distasteful, malodorous secretions (remember osmeteria
in swallowtail caterpillars, for instance). Predators must learn/be trained about these signals.
Insect-Plant Interactions -- Chap. 9
Estimates are that approximately half of all insects are phytophagous
including a majority of the members of the six largest orders. Indeed, insects are the most
important consumers of plants on the face of the planet. Not all interactions are injurious,
however. The main pollinators of angiosperms (flowering plants) are also insects, without
which we would not have most fruits, nuts, berries, etc.
Pollination is the point, but plants must offer or pretend to offer a reward -- usually nectar.
The benefits for both: 1) Plants -- produce less pollen than for those that are wind-pollinated;
insects numerous; 2) Insects -- guaranteed (almost) food source
Required plants to develop colorful targets B brightly colored petals (including in UV) --
and/or strong odors, especially for attracting nighttime pollinators. Odors may be pleasant, but
some species have fleshlike odors, or odors that are pheromone mimics (so males visit the flowers
and pollinate them while trying to mate with the flower). Some New World orchids are pollinated
specifically by Orchid Bees -- the orchids provide males with compounds that can be used to
attract females; but males must go through the "trap" in the flower to get out and pick up pollen.
Nectar seems exclusively developed to meet nutritional needs of favored pollinators.
Indeed, the success (diversity) of Lepidoptera, Hymenoptera and Diptera can probably partially
be explained by the development of nutritious nectar. The most common flower visitors: Leps,
Hymenops, Dips, and Coleoptera. Though many, particularly the hymenopterans, are important
pollinators, many species will eat pollen, and others, particularly the beetles, will eat other flower
parts as well. A wide variety of the first three orders visit flowers, but in beetles flower visiting is
exhibited mostly by cantharids, some cerambycids, some scarabs, some meloids, and a few others.
-lecty -- constancy of visiting flower species; (monolectic, oligolectic, polylectic).
Monolecty is, of course, most beneficial for plants; interestingly, monolecty may also be at least
temporarily beneficial to the insect, especially with density of flower availability, as the insect can
form a powerful search image and learn a specific flower "mechanism". There are plenty of
flower visitors that are oligo- or polylectic, however.
Examples of complete pollnator-flower mutualism (a coevolutionary relationship): 1) Some
orchids and Orchid Bees; 2) Figs and Fig Wasps; 3) Yucca and Yucca Moths
External Feeding -- leaf feeders, sap/stem feeders, fruits, seeds, petals/flowers
External feeders are themselves exposed to predators, etc., and are usually protected by
chemicals and often brightly colored.
Internal Feeding -- Miners inside of leaves; borers in stems/roots, fruits/seeds; galls
Monophagy (specialists), Oligophagy, Polyphagy (generalists)
Many plants have developed secondary plant compounds for defense; but some species
of insects have overcome and even utilize these defensive compounds. Although some of these
compounds are poisons, other plants have produced juvenile hormone analogs, to disrupt
development. Many plants also stimulated into more growth by insect feeding.
Choice of feeding/oviposition based on plant chemicals detected by the insects.
Insect-Insect Interactions -- specifically Entomophagy; Chap. 10.
Though insects are typically near the bottom of the consumer chain, or, in other words,
typically food for the larger animals of the world, a number of insects are also feeders on other
insects. These interactions fall into one of three catergories: 1) predator-prey, 2) parasites
(ecto- and endoparasites), and 3) parasitoids. -- "intermediate" between predator and parasite.
Further specialized types of relationships can be defined, such as cleptoparasites, which
lay eggs in other species nests which hatch and kill other larvae already present and eating the
provisions of the nest. Social parasitism, where a "parasitic" queen takes over the role of queen
(certain bumblebee species) and slavery where pupae are hijacked and the hatching adults then
take care of the activities in the nest (certain ant species) are practiced by certain hymenopteran
species. Phoresy is transporting of one insect species by another -- this does not specifically harm
any individual. However, adult female parasites/parasitoids may be phoretic, hopping off when
the host lays eggs to lay her own eggs on the host eggs.
Predatory relationships -- some predaceous as adults, some as larvae, a majority in both stages.
Good eyesight is essential. As with plant feeders, predators can be monophagous, oligophagous,
polyphagous. Strategies can include: 1. "random" searches (frequent in walking predators/ground
dwellers, especially Coleoptera and some neuropteran larvae; egg predators would fall into this
category), 2. hunting (orient to prey at distance using visual or chemical cues;very common for aquatic
and aerial insects, though may include ground dwellers like ants using chemicals to orient), 3. ambush
(sit and wait; works in aquatic and terrestrial environments; ambush/assassin bugs and mantids are
well-known examples), and 4. trapping (ant lions, some caddisfly larvae; also includes species that
use light to attract prey). You will be responsible for examples of each.
Parasitoids include mostly certain dipteran and hymenopteran families. Hosts are typically
larvae of various insects, particularly coleopteran/lepidopteran species, but also other Hymenoptera,
Diptera, and several other orders, particularly Orthoptera and certain Hemiptera. Some parasitoids
(Ichneumonoids) have viral DNA that they inject with their eggs -- the virus disarms the ability of
the host to encapsulate the egg. Aquatic families are largely untouched by other insect parasitoids.
True insect parasites on other insects are rare. A few flies and wasps are parasitic;
strepsipterans are perhaps the most familiar example.
Insects and Microbes --
Chapter 11; as in previous chapters, KNOW EXAMPLES.
See Table 11.1, page 246 for types of Insect/Microbe relationships
"Microbes" can be food -- fungus/algae/other microorganism feeding; can be part of
detritus fed upon by decomposers; don't forget that some ants and termites grow fungal farms.
Some aquatic species are filter feeders, feeding on organic debris and planktonic organisms.
Symbioses -- Definitions:
Mutualism -- a symbiosis where both organisms benefit; can occur with microbes or
Obligate symbiosis -- both host and symbiote require the relationship
Facultative symbiosis -- host can live without symbiote
Commensals -- symbiotes that do not harm or benefit "host"
Examples (some of which you should already know!)
Various microorganisms aid wood-feeding species in digesting wood.
Heteroptera with microorganisms in gut pouches
Polydnaviruses deposited with ichneumon/braconid wasp eggs inside host to suppress
host's hemocyte immune response.
There are several examples of other microbes found in guts of various insect species
where the insects are not adversely affected if the microbes are removed.
And, of course, the microbes for which insects are vectors are technically facultative.
Insect pathogens are typically viruses, bacteria, fungi, protozoans or nematodes.
Many are specific to certain hosts; some are facultative, only becoming virulent after
entering hemocoel through wounds or disruptions in digestive tract.
Viral -- Baculoviruses, including nuclear polyhedrosis viruses; common pathogens of
larval lepidopterans (AAHH!). They are encapsulated in a thick protein coat, protecting them
from degradation in the environment; they therefore persist outside the host for a time. These
viruses, once ingested, infest host tissue, slowing development initially, which is favorable to virus
reproduction. As the virus multiplies and breaks down cells, the cuticle thins, becoming easily torn,
and the body contents liquefy, turning black in a grotesque death. Body fluids ooze onto surroun-
ding surfaces, quickly infecting other individuals that come in contact with the fluids. Obviously
useful for biological control, though specificity may be low. (See Table 11.2, page 251)
Bacterial -- few bacteria actually infest insects; the immune system of insects is relatively
effective against potential bacterial pathogens. Bacillus thuringiensis, however, is toxic to a
number of species of insects, mostly in the larval stages of endopterygotes. Different strains are
used in biological control for larval lepidopterans (Gypsy Moth control), mosquitos and blackflies,
some damaging chrysomelid beetles, etc. B. thuringiensis is not particularly persistent in the
environment, however. Some other bacteria may be more persistent and host specific, controlling
scarabs and their grubs (Japanese Beetles), certain flies (and larvae), leafhoppers, etc.
Protozoans -- not so much infectors of insects as vertebrates; insects are vectors for
protozoan diseases such as malaria (mosquitos), Chagas' disease (reduviids), African sleeping
sickness (Tsetse flies). Pebrine disease of Silkworms (Bombyx mori) is caused by a protozoan.
Fungal -- perhaps the commonest of insect pathogens. Spores of infectious fungi typically
germinate on the cuticle, and the hyphae ("roots") grow inward, invading the hemocoel. Toxins
exuded by fungi may cause death, or death may be slower as fungi turn insect tissues into fungal
growth. Infected individuals show behavioral changes before death, often crawling to the tops
of plant stems which probably aids the new fungal spores in dispersal. Many fungal pathogens
require very specific temp and humidity conditions to grow, and have therefore never been
cultured in the lab, meaning, unfortunately, that these are of limited use in insect control. Some
have been useful in controlling aphids (and others) in humid, temperature controlled greenhouses.
Nematodes -- small roundworms; a few species are striking parasitoids of insects, often
attaining relatively large size in the infested host before killing the host as it emerges. Some life
stage of the nematodes are capable of free life or persist dormant in the soil until the next suitable
host is encountered.
Insects as Vectors of disease -- (Chapter 11, pgs. 256-259, Chapter 12, pgs. 263-272)
No great detail to learn here, other than awareness of the large number of diseases carried
by insects, for both animals and (crop) plants. You will be responsible for knowing at least some
examples of both plant and animal diseases vectored by insects (see Table 11.3, pgs. 252-253,
and Table 12.1, page 265).
Beneficial/Injurious Insects -- Summary (see chap. 1, pgs. 13 - 15; we=ve covered examples in
different orders, and discussed this topic in chapters 8 - 11)
Pollinators of crop plants/orchard trees
Meat production (some), as some plant materials used to feed domestic animals require
Silk (produce by the completely domesticated Silk Moth)
Biological control -- extremely important in control of many insect and plant pests
Detritivores/decomposers incredibly important -- useful in scientific collections (to clean
bones of flesh, for instance)
Crop plant part eaters
Stored agricultural product pests
Parasites and transmitters of disease of humans/domestic animals
Pests on collections -- of importance in the scientific community
Non-native insects may displace native species -- the rest of the honeybee story
Pest Management --
Our previous discussion of injurious insects, and the above discussion of pathogens of
insects leads directly into the discussion of pest management. There are, of course, several
different courses of action that may be taken against pest insects, some of which we have already
discussed under various topics. These will be summarized (some of them reviewed) here.
Pesticide use is, of course, a familiar concept, but also a controversial one. Some
pesticides, though very effective on insects, are extremely persistent in the environment, and may
cause adverse affects on other organisms (including cancer and developmental abnormalities), and
may even be concentrated in tissues through biological amplification. Also, a number of insect
species develop resistance with continued application of one insecticide. As such, most strategies
now use a combination of less toxic insecticides with a variety of other approaches that are less
environmentally and socially damaging, an approach called Integrated Pest Management (IPM).
Methods of Pest Management
Chemical -- inorganic chemicals, organic chemicals (including botanicals and synthetic).
Insect growth regulators -- juvenile hormone analogs and chitin synthesis inhibitors;
prevent maturation and therefore eventually reproduction.
Microbial -- See Pathogens, above; Bacillus thuringiensis control for Gypsy Moths;
B. popillae for Japanese Beetles; polyhedral viruses; certain nematodes; etc.
Effectiveness dependent on dosage, combinations of methods used (including rotation of
insecticides), persistence, specificity, genetic resistance/variability of pest. Problems besides
direct health problems for humans include specificity and persistence.
Biological Control -- involves importing natural enemies or artificially increasing numbers of
natural enemies (in the lab) and releasing them. Specificity of enemies is critically important here.
Host Plant Resistance
Cultural Controls -- includes timing of planting/harvesting, tilling, weeding (removes
alternative food) and crop rotation.
Pheromones and attractants -- pheromones of many species have been synthesized, and may
be used in traps to prevent mating (sesiid, tortricid, and Gypsy moths); carbon dioxide is an
attractant used in some mosquito traps.
Genetic engineering has been applied to both sets of organisms involved here, the insects
and the plants.
Plants -- several species of plants have had genes for producing certain secondary plant
compounds or bacterial toxins that give them protection from certain insect pests; for example,
B. thuringiensis toxins have been genetically engineered into cotton and corn since 1995. There
is a problem, however, in that in some cases toxins may expressed in the parts of the plants we
plan on eating. And, of course, after a time, insects may build up resistance in some cases.
Insects -- one of the main examples of genetic alteration of insects involves the
Screwworm Fly, a serious pest of livestock. Large numbers are reared in the lab, irradiated
(which alters the genes and makes them sterile), and the sterile males are then mass released early
in the year when natural population numbers are low; females mating with these sterile males
produce non-fertile eggs.