Tropism in insects & insect communication

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Dr. T. KRISHNA CHAITANYA
Assistant Professor (Agricultural Entomology)
School of Agricultural Science & Technology, NMIMS, Shirpur
ENTO 131 - Fundamentals of Entomology (3+1)

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Tropism in insects &
Insect communication

3. • Herbivores are monophages, oligophages and polyphages.
• These defenses are either physical (spines, pubescence on stems and
leaves, silica or sclerenchyma in leaf tissue etc.) or chemical
(secondary plant compounds-tannins, terpenoids, alkaloids etc.) in
nature.
• Secondary plant compounds may either repel an insect for feeding and
oviposition or affect the biology of an insect due to antibiosis.
• Insects are intimately associated with plant and are important to many
plants in their reproduction, through pollination or seed dispersal.
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4. Insects (Entomophily) can facilitate the pollination, similarly can
Wind (Anemophily), Water (Hydrophily), Animals (Zoophily).
Entomophily - Insect pollination
(i) Cantharophily -beetle pollination
(ii) Myophily -fly pollination
(iii) Sphecophily- Wasp pollination
(iv) Myrmecophily- ant pollination
(v) Melittophily-bee pollination
(vi) Phalaenophily-moth pollinated
(vii) Psycophily- butterfly pollinated
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5. • Insect-plant interactions associated with pollination are clearly
mutualistic. The plant is fertilized by appropriate pollen, while the
insect obtains food. E.g. (i) Fig species pollinated by fig wasp. The
female wasp enters the fig syconium via the ostiole
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7. (ii) Correlation between moth proboscis length and flower depths -
Madagascar star orchid with 30 cm length of flower parts is pollinated by
giant hawk moth with long proboscis.
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8. • Ants and seed dispersal: Many ants feed on seeds and also helps in
dispersal of seed, known as myrmecochory.
• ‘Phytotelmata' (Plant held water containers): Many plants support
insect communities in structures that retain water. In this process plant
also derive some nutrition from insects. e.g. Pitcher plants.
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9. Insect communication
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10. Insects generally communicate to locate their food source
and mate, using
(i) Semiochemicals
(ii) Light Production
(iii) Sound Production
(iv) Body language
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11. I. SEMIOCHEMICALS
a. Pheromones: "substances that are secreted to the outside by an
individual and received by a second individual of the same species in
which they release a specific reaction".
(i) Female lepidoptera - eversible sacs or pouches between the 8th and
9th abdominal segment.
(ii) Female honey bee - mandibular glands
(iii) Female aphids - hind tibia
(iv) Female cockroach - midgut
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12. Further classification of pheromones is based on categories of behaviour
associated with sex, aggregation, spacing, trial forming and alarms.
(i) Sex Phermones: Used for mate location and courtship (eg) Queen
butterfly Danaus gilippus : Male insect produces courtship pheromone
an alkaloid called danaidone.
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13. (ii) Aggregation pheromones: Causes insects of both sexes to crowd
around the source of the pheromone. This may lead to increased chances
of mating. The other benefits being, security from predation, maximum
utilization of scarce food resource, overcoming of host resistance and
cohesion of social insects. e.g. Cockroaches and scolytid beetles.
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14. (iii) Spacing phermones: Produces appropriate spacing on food
resources. (eg) Many _Tephritid_ flies lay eggs singly in fruit where a
single maggot is to develop. Here the female deposits an oviposition
deterrent pheromone on the fruit to avoid subsequent oviposition.
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15. (iv) Trial - marking pheromones: Many social insects use this
pheromone to mark their trails to food and the nest. This pheromone is
volatile and short-lived. (eg) In ants the trial pheromone are commonly
metabolic waste products excreted by the poison gland. These need not
be species specific - several species share some common chemicals.
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16. (v) Alarm pheromones: This causes alarm behaviour. Alarm is
provoked by the presence of predator or in many social insects by the
threat to the nest.
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17. II. Light production: The principal role of light emission is in courtship
signaling and prey finding. This involves species specific variation in
duration, number and rate of flashes in a pattern and the frequency of
repetition of the pattern. (eg) Lampyrid beetle (fire fly)
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18. III. Sound Production: It is useful in location of mate. (eg) Mosquitoes,
Cicada.
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19. IV. Body Language (The dance language of bees)
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Karl von Frisch
Nobel Prize in Physiology
or Medicine (1973)

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