Intrinsic and extrinsic factors affect insect communities. Intrinsic factors include biotic interactions between members of the same and other species through food sources, competition, and symbiotic relationships. Extrinsic abiotic factors that influence insect communities are temperatures, humidity, light, soil conditions, and human activities through changing habitats, applying pesticides, and transporting insect species.

1. INTRINSIC AND EXTRINSIC
FACTORS AFFECTING INSECT
COMMUNITY

2. Outline
 Introduction
 Intrinsic factors
 Biotic factors
 Food, source
 Homotypal effect
 Heterotypal effect
 Extrinsic factors
 Abiotic factors
 Temperatures
 Humidity
 Light
 Medium (soil)- edaphic factors
 Anthropogenic factors
 Impact of human activities

3. Introduction
 Insect community is affected by a couple of factors, some of these
factors are as a result of interaction of the insect communities on
basis of how they compete for nutrients, space and mates
(reproduction success).
 Other factors as a result of interaction between the insect and the
environment factors such as temperature, humidity, light, and
mediums e.g. soil, rocks etc.
 Human also affect hugely on insect colonies through various actions
which human take in a move made to control or completely eradicate
insects from a given are.

4. Diagrams of factors affecting insect community
teTEMPERATURE
RAIN
LIGHT
PESTICIDES
INSECT COMMUNITY
OTHER MEMBEROF
SAME SPECIES
COMPETITORS
FOOD SOURCES
NATURAL ENEMNIES
WIND

5. Intrinsic factors
 These factors which emanate from the insect community interaction and a result the factors
are biotic.
 FOOD SOURCE/NOURISHMENT
 Food is a key element in maintaining any insect community.
 There are many nutritional modes of life of insect.
 Hylophagous (insect which eat organic matter)
 Necrophagous- eat dead zoogenic matter.
 Saprophagous – eat dead phytogenic matter.
 Coprophagous – eat the dung of higher animals

6. Food/nourishment cont..
 Biophagous (eat living organic matter)
Phytophagous (herbivor) – eat loving
phytogenic matter.
Zoophagous (carnivor) - eat living zoogenic
matter.
o Parasites –live on higher animal but not
killing it.
o Parasitoids –live on higher species and
finally kill it.
o Episite or predators- immediately kill

7. Food and nourishment cont..
Degree of food specialization of pest
 Monophagous pest e.g. pea beetle – Bruchus pisorum
 Specialize in feeding of a single plant species.
 Oligophagous pest e.g. potato beetle – Leptinotarsa decemlineata
 Generally specialize in feeding of the species of given plant family.
 Polyphagous pest e.g. Noctua- Agrotis segetum, Agriotes spp.
(wireworms), Melolontha spp. (chafers) eg locust, tomato spider mite
.
 Can feed on species of totally different plant species.
 Pantophagous pest (cockroaches – Blatta spp)
 Can feed on living and non living materials derived from plant and
animal. E.g. these cockroaches feed on plants and rats too.

8. Food and nourishment cont..
 Specialist insect community i.e insects with a tight
nutritional spectrum is most affected incase of absence of
such food.
 On the other hand Opportunist insect communities i.e
insect with a wide food spectrum stand a better chance of
survival in case of absence of one type or source of food.
 Changing the food source: is rare phenomena when
different developmental stages of the same insect species
eat several food e.g. numerous ichneumons are
parasitoids as larvae but feed on pollen and nectar of
flower as adults.

9. Food and nourishment cont..
 Food parameters can affect on the efficacy of reproduction, the
number of offspring and their growth and development e.g. in the
case of lamellicorn beetles e.g. stag-beetle fewer, smaller and
infertile adults develop feeding on improper additional food.
 Quantity and quality of food can influence the development of insect
e.g. in case of bees, well nourished larvae develop to queens, but
underfed larvae develop to worker-bees.
 Female insect generally require more and better quality food than
male.

10. Homotypal effect (members of same
species)
 Two phenomena are evident here.
 One if individuals are too many the population of the community start
decreasing i.e outbreak.
 The other is if the individuals are too few the female and male cant
find each other thus a further decrease in population number due to
few offspring's.
 Many species need a continuous contact with their companions “group
effect” e.g. social insects such as migratory locust.

11. Homotypal effect (members of same
species)
 Competition: is an interaction between organisms or species in which the fitness
of one is lowered by the presence of another.
 Limited supply of at least one source (such as food, water and territory) used by
both is required.
 Intraspecific competition: this is competition
among individuals of the same species is referred
to as intraspecific competition.
 Interspecific competition: a form of competition in
which individuals of different species compete for
the same resource in habitat.

12. Heterotypal effect (members of other species)
 Heterotypal effect: individuals of different species co-exist in a
habitat and one of them has an effect on the other or both have an
effect on each other.
 Probiosis : an association of two organisms that enhance the life
process of both e.g. bees and flowering plant.
 Parabiosis: the union of two animals where one organism benefits but
the other is unaffected.
 Commensalism: e.g. cabbage seed weevil/ Ceutorhynchus
obstrictus and Braciscca pod midge/ Dasineura brassicae.
 Add content.

13. Heterotypal effect cont..
 Symbiosis: is a close prolonged association between two or more
different organisms of different species that may, but does not
necessary, benefit each member.
 Symfilia: association between two species when a social insect
provide shelter for another insect in exchange fort its secretion
(e.g.: ants and aphids).
 Antibiosis: an association between two or more organism that is
detrimental to at least one of them.
 Predation: an interaction where a predator ( an organism that is
hunting) feed on its prey (the organism that is attacked) the act
of predation always results in the death of the prey and is neve
to its benefit e.g. hornets to bees.

14. Heterotypal effect cont..
Parasitism: relationship between
organism of different species where one
organism the parasite benefit at the
expense of the host.
Parasitoids: parasitoids are organisms
living in or on their host and feeding
directly upon it, eventually leading to
its death. E.g. parasitoid wasps on
lepidopteran eggs and larvae

15. Extrinsic factors
 There factors which affect insect communities
which are from the environment and non-living
i.e abiotic factors.
 These include:
Temperature
Light
Humidity
Medium i.e air and soil

16. Temperature
 Temperature does influence many activities in insect and their
community.
 Bulk of insect die on 40-60o (killing effect depend on the duration of
high temperature).
 owing to their ecological plasticity insect are able to adapt and
become acclimatized to the changing environment enlarging the
boundaries of the tolerance temperature zone (it can be supported by
global warming e.g Helicoverpa armigera).
 In the temperate zone minimum temperatures during winter season
determine the northward spread of insect.

17. Temperature cont..
 Other activities of insect affected by temperature include:
feeding, development and reproduction.
 Developmental rate of insect is highly influenced by the
temperature, it can come off only above the biological zero
point or developmental threshold temperature.
 Insect species living in the temperate zone need to have a
developmental stage which is able to survive the long and cold
winter period.
 Degree day
 Temperature threshold
 Paper abdel mutalab

18. Humidity
 Depending on the type of biotope we generally study the relative
humidity, soil moisture or moisture content of plant (or plant parts).
 Its is obvious that all insects species have a concrete claim to water as
well.
 There are euryhygric i.e able to withstand a wide range o humidity
and stenohygrics species ( e.g. owing to its semi-arid origin, potato
beetle is an extremely euryhygr beetles which can survive the 50% loss
of its body’s water content.
 Humidity can also affect on the behavior of insect e.g. insects
overwintering as adult emerge earlier in case of dry soil/litter;
wireworms can move slower in wet soil.

19. Humidity cont..
 In case of many insects, embryonic development can start only after
the egg absorbed some water e.g. may-beetle, rape saw-fly.
 Liquid water can be dangerous to insect e.g. young larvae of potato
beetle can show 60% mortality because of the thunder-shower.
Interestingly opposite the potato beetle adult can survive till two
weeks on the surface of water.
 Humidity (together with temperature) effect on the developmental
rate and reproduction e.g. meal-mite require about 13% humidity for
optimal reproduction.

20. Light
 Energy of natural biotypes is derives almost entirely from the radiating sun.
 There are several parameters of light which affect insect.
 These include:
 Intensity
 Current position of the sun in the sky.
 Wave length (colour)
 Polarization
 Photoperiod.

21. Light intensity
 Light intensity may be dangerous to insect species living in dark places e.g.
soil or in caves due to the ultraviolet radiation of sunlight.
 Light intensity affect insect activity both on the nocturnal and diurnal insect.
 E.g for the case of diurnal insect.
 Exogenous rhythm (swarming start from dusk) e.g. the European
cockchafer- Melolontha Melolontha.
 Endogenous rhythm (controlled by inner clock) European grapevine moth-
Lobesia botrana

22. Light current position of the sun in the
sky
 This plays a major role in the spatial orientation of the insects.
 Phototaxis: the positive or negative response of a freely moving organism
towards or away from light (light traps: e.g. European borer).
 Other insects can use the current position of the sun in the sky for spatial
orientation eg potato beetles always move at the same angle to light
direction while searching for food plants.
 Honey bees use the angle of the bee-hive and light direction; they can
orientate within the dark hive owing to their inner clock they can correct
the angle of light direction and flight direction (honey bee dance, tail
wagging dance).

23. Light current position of the sun in the
sky
 Direction of the dance differs
from the vertical in the same
angle as the food source takes to
the sun.
 Duration of the dance shows the
distance of the food source from
the beehive.

24. Light wave length
 There are significant difference in
colour vision of insect.
 Honey bees can perceive
ultraviolet light as a colour, but
cannot see the red colour.
 Wave length has an effect on
insect behavior (colour traps e.g.
yellow plate attract whiteflies
while blue plate attract aphids
and thrips.

25. Light polarization
 Light is an electromagnetic wave.
 Light polarization is a property of light wave, which
describe the direction of their oscillation vibration owing
to solid particles within the atmosphere; its direction
depends on the position of the sun on the sky.
 All social insect can perceive light polarization, which
makes them possible to orientate in cloudy weather
accurately( when light direction cannot be used).

26. Light photoperiod
 Its is duration of bright (photophase) and dark
(skotophase) period within one day.
 Mainly in the temperate zone it decisively determines the
development of many species.
 It can cause morphological changes e.g. in case of 16
hours photophase or even more Euscelis plebujus (cicada)
develops to a so called (forma plebejus) with longer
wings, but under 16 hours photophase it develops to a
shorter winged (forma incises).

27. Medium
 The two medium i.e air and soil impact highly on the insect
community.
AIR
 Only a temporary space where insect many occur.
 Tiny wingless insect utilizing the ascending warm air currents were
caught in surprising height (4500).
 Air pressure changes have an effect on the behavior of insects too,
generally all insect hide in windy weather.
 Insect which are capable of flying, they generally fly against the
breeze and have them carried by the wind.

28. Medium cont..
SOIL
 Physical and chemical parameters of soil have effects on soil-borne
insects e.g. Agriotes spp wireworms prefer soils with a pH of 4.0-5.5.
 Soil organic matter is important food source for cockchafer grubs and
wireworms in their early larval stages.
 CO2 soil content affect insect too e.g. Melolontha melolontha larva
can survive in soils saturated with CO2 for a up to a month.
 Physical aspects of soil influence insect too e.g. Zabrus tenebrioides
(ground beetles important cereal pest) cannot live through in loose
sandy soils because its larvae requires loam to make their vertical
tubes in soil.

29. Anthropogenic factors
 All the effect derive from human activities are able to
change the habitat the species composition of biotic
communities the size of population more over the
condition of the planet.
 Changing of natural flora: vast expanse deforestation and
giving place to plant production.
 Technologies of plant production and plant protection:
applying of pesticides e.g. DDT.
 Building-up artificial habitats: emergence of synanthropic
species living nearby the man e.g. stored products pests;
cockroaches and bugs.

30. Anthropogenic factors
 Intended and accidental movement/ transport of
useful and harmful species: colonizing natural
enemies of a new pest from its original home
(successful and unsuccessful attempts).
 Environment load and pollution: toxic organic,
inorganic, synthetic and radioactive materials