INSECT ECOLOGY

 Ecology is one of the disciplines of a much broader area of action covered by environmental science . Lcology concerns the processes dealing with what limit life , how living things interact with their surroundings and how living things make use of the resources .

 Ecology , the term proposed by a German biologist " Ernst Haeckel " during the year 1869. The study of the interrelationships between organisms and their environment is termed " Ecology " . According to different scientists the ecology has been defined as :

 Standford ( 1907 ) ; Life needs and house keeping habits of an organism .

 Clements ( 1916 ) : Science of community

 Odum ( 1971 ) : Study of organisms at home , 

Peter Price ( 1975 ) : Science of relationship of organisms to their nature . 

Environment and its components 

Environmental science , on other hand , deals with the application of this knowledge for managing the environment . Clark etal . ( 1967 ) - defined the environment of the population as everything external to the population that influences its abundance and evolution . According to Andrewartha and Birch ( 1954 ) , the environment of an individual organism may be analysed into four components , viz . , weather other organisms , food and a place to live . The four components were said to comprise everything that might influence an organism's chance to survive and multiply . 

 components of Environment

 Weather : Temperature , Light , Humidity , Rainfall . Wind etc.

 Food : Quality and quantity

Organisms: Plants and animals

 Place: Habitat

 EFFECT OF ABIOTIC FACTORS

 Temperature:

 It has got a profound influence on the life cycle of insects by affecting the number of generations.  Normal life activities go on smoothly at a specific temperature called optimum range of temperature.  The rate of chemical reactions and metabolic processes are influenced by temperature, insect enter diapause if the temperature is below optimum called hibernation or above optimum called aestivation.  Influence on fecundity: 0.g. 

 (1) Diamond back moth (DBM) lays more eggs at a temperature of 18 ° C than 22 ° C. 

 (ii) Grasshopper lays 20 to 30 times more eggs at 32 ° C than 22 ° C. 

 (iii) Oviposition of bedbug is inhibited at 8 ° C to 10 ° C.  Other effects:

 (i) High temperature induces more early shoot borer attack in sugarcane. 

 (ii) Larval period of sugarcane internode borer is shortened 16–24 days in summer and prolonged 141–171 days during winter.

  (ii) Desert locust Shistoceres gregaria swarms at 17'C to 20'C.

  Light:

 The influence of light on some insects are: (i) In ahids short day length produces sexual forms and long day length produces asexual forms like parthenogenetic viviparous reproduction (ii) Frut flies, Tephritids lay eggs only in light.  (iii) Codling moth, cotton bollworm Earias spp.  Red hairy caterpillar oviposit in dark.

 Humidity:

 Insect exhibit the phenomenon of humidity preferendum also like that of temperature.  The have a tendency to congregate within a narrow range of humidity and that range is the preferred humidity.e.g. 

 (I) High humidity induces the incidence of BPH in rice and aphids in other crops.

  (ii) Termites usually move towards a zone of high humidity when subjected to the slightest desiccation.  Termites showed a humidity preferendum of 90-95% RH and they live longer at 100% RH under starved condition.

  (iii) Migratory locust, Locusta migratoria failed to produce eggs at 40% RH but at 70% RH, it sexually matures. 

 (iv) Rice weevil, Sitiphilus oryzae fecundity is less at 34% RH and maximum at 70% RH.

 Rainfall:

 Some of the effects of rainfall on the biology of insectes

 (1) In red hairy caterpillar and cutworms rainfall is essential for adult emergence and pupation.

 (2) Excess rainfall brings the white grubs to soil surface so that get predated by birds.

  (3)Excess rainfall controls aphids and DBM

 (iv) Intermittent low rainfall increases BPH and thrips incidence in rice.

 Wind:

 Wind is of great value to insect displacement and therefore, affect population changes by influencing the numbers into or out of an area .

(1) Mostinsects will  not take flight when the speed of wind exceeds the normal night speed .(2) Strong flying insects tend to fly with the winds during migration and are displaced long distances as in case of spruce budworm moth.

 (iii) Aphids and lenthoppers are being blown thousands.  of kilometres,

 (iv) Helicoverpa adults ily up to 90 km with the help og wind current,

 (v) Air movement may be directly responsible for the death of insects.

 (vi) Severe wind coupled with heavy rains may cause morality.

 topographic factors:

 Besides mountains, lake, sen etc.  Also act as physical barrier for the spread.

  Soil type:

 plays an important role in the multiplication of insect species.  Wireworms multiply in heavy clny soil with poor drainage and white grubs multiply in loose sandy soil with better drainage.

 water: 

Standing water helps in the multiplication of insects like mosquitoes and certain beetles.  Running water stream is preferred by odonates and cadis flies etc,

EFFECT OF BIOTIC FACTORS

 Food:

 Quality and quantity of food play an important role in its survival.  longevity.  distribution, reproduction and speed of development, etc. 

 Quantity of food:

 When there is relatively small number of individuals per unit quantity of food, there is enough for all to grow to adulthood but in the scarcity of food, only these develop rapidly to become adulthood, while the slower ones do not develop.  More than one species consuming the same food will naturally reduce the total amount available for any of them.

 quality of food:

 Egg production, larval development, longevity and size of insects may be greatly influenced by the quality of food.  Many insects species store sufficient nutrients during the larval stage to accomplish adult activities.  The queen of honey bee and termites lay eggs for almost all of their adult lives and require food constantly.  The differences between workers and queen honeybee depend entirely on the diet that each receives during larval development.  They feed workers larvae only for three days and queen larvae continue to be fed on royal jelly.  Changes in the quality of food induce the appearance of winged forms and migratory behavior in aphids.

 competition

 competition includes all those interactions among different species which adversely affect their growth and survival.  The interaction between the individuals of the same species is called intraspecific and between those of different species is called inerspecific.

 intraspecific intractions are the following: 

Aggregation:-

 Aggregation refers to the tendency of some insects to concentrate in numbers larger than found in normal distribution and congregate under various  circumstances by their own movements eg  homopterans (species of membracids).

  Concurrence:

 They crowd together in mass assemblance at one time for feeding or hibernating eg Coccinelids, Pieris butterflies dragonflies armyworms. 

 Cannibalism:

 It takes place between members of the same species.  Large larvae and adults may feed on eggs and small larvae of their own species or older adults encounter the younger stages

Association of the sexes:

 The sex ratio in insects plays an important part in the build up of their population at the same temperature.  If the sex ratio of a house fly at normal temperature is 1: 1, then there will be 2 x 60 flies at the end of breeding season.

  Parental care:

 It includes care of eggs and broods also provision of larval food either on the plant itself or providing food material from outside.e.g.  dung beetle, earwings and mole cricket.

  Social life:

 ants, termites, wasps and honeybees live in a family colonies that have a division of labor among individuals and an interchange and sharing of food and other things among members of the colony.

  Interspecific intractions are the following: 

Commensalisms:-

 It is an unbalanced relationship in which one of the partner is benefitted and the other remaining unbenefitted and unharmed.e.g.  Staphylinid beetles inhabit nests of ants as commensals.

  Mutualism or Symbiosis:

 It is the relationship in which both the partners are benefitted egAnts feed on honeydew secreted by aphid actively produce 'milk' to obtain honeydew.Insect that feed on pollen and nectar have a mutualistic relationship to their plant hosts as they carry  it to the next flower and thus helps in pollination.

  Parasitism:

 It is the relationship in which one species benefits at the expense of another.e.g.  facultative parasites like biting flies, lice and ſeas.  Parasitoids are mostly Hymenoptera and Diptera (especially Tachinidae).

  Predatism:

 A predator kills but never eliminates the prey completely.  Preying mantis prey on many insects like larvae, nymphs and leaf hoppers.Crusoperla on aphids jassids and Coccinella on aphids.

  Natural enemies includes (a) parasites and (b) predators. 

 Environmental resistance

 The sum total of all factors in an environment that tend to reduce the rate of multiplication of an insect is known as environmental resistance.  The major factors responsible for the environmental resistance are physical, chemical, nutritional host plant and biotic factors.

  Physical factors

 include temperature, light and moisture and water.  The physical condition in a locality influence the rate and development of insects,

Chemical factors

 concentration of O, and Co, in the given medium is considered as chemical factors chemical present in the host decides the host selection and make an insect monophagous oligophagous and polyphagous.Amino acid and asparagin decides the development of BPH in rice,

 Nutritional factor  :

 Availability of food regulates population abundance and influence life cycle, sex ratio and fertility factors.

  Host plant associated factors:

 Plant characters like thorn, wax, bairness and thick cuticle interferes the normal feeding and oviposition.

  Biotic factors includes parasites and predators.

  CATEGORIES OF PEST

 Pest:

 Any animal which is noxious, destructive or troublesome to man or his interests.

  Categories of pests:
 Based on occurrence
 regular pest:

 One occurring more frequently on a crop having close association.  E.g.  Rice stem borer, Brinjal shoot and fruit borer etc.

  Occasional pest:

 One occurring infrequently in those causing damage at irregular interval with on close association.e.g.caseworm in rice.  mango stem borer etc.

 Seasonal pest:

 One occurs during a particular part of the year or season in particular crop.year after year.e.g.Red hairy caterpillar on ground nut, mangohoppers during flowering season.

  Persistent pest:

 One occurs on a crop almost throughout the year and is very difficult to control.e.g.Thrips in chilli, mealy bug in guava.

  Sporadic pest:

 One occurring in a few isolated localities.e.g. Coconut slug caterpillar, slug caterpillar on castor and rice gundhi bug etc.

  Based on level of infestation

 Epidemic pest:

 Occurrence of pest in a severe form in a region or locality at particular season or time.e.g.BPH in Tanjore during October and November.

  Endemic pest:

 Occurrence of pest in a low level in few pockets or contined to a particular area..BPH in North Bihar.Cutworm in Mokama.

  Based on the loss

Major pest:

 Insects which cause a loss of 10% or more of yiel are called as major pests.

  Minor pests:

 Those which normally cause a loss ranging from 5-10% (less than 10%). 

 Key pests:

 A pest which causes major damage every season unless controlled is regular as key pests.

  Potential pests:

 These pests normally cause negligible damage but may become highly destructive resulting from some disturbance in the environment and the consequent increase in their number e.g.  armyworm on wheat. 

 The status of the pest can be assessed by observing the cost - benefit ratio.