Insect Pests of Fruit, Plantation, Medicinal & Aromatic Crops (2+1)

Insect ecology

Websters dictionary meaning

• Totality (or) Pattern of relation between organisms and their environment. A German biologist ‘Ernst Haeckel (1869) proposed the term ‘ecology’. This deals with total relationship of an animal to both its organic and inorganic environment.
Insect ecology

• Science of insect in relation to their environment.
Habitat ecology

• Study of habitat and its effects on the organism. Autoecology: Study of an individual, its behaviour and the influence of environment on its life cycle.
Syn ecology

• Study of a group of organism which are found as a unit. It is also called Community ecology.
Ecosystem

• A self containing habitat in which living organisms and the physiochemical environment interact in an exchange of energe and matter to form a continuing cycle.
Biotic balance

• It is the condition of equilibrium in the population of animals. It is not a static one but oscillating. The population level is determined by I. Reproductive potential and II. Environmental Resistance.
I. Reproductive potential

• The ability of an insect to multiply in a given time in the absence of environmental resistance. Factors that affect the reproductive potential are a) initial population by fecundity. c) Length of developmental period and d) sex ratio.
II. Environmental resistance

• The sum total of all factors in on environment that tends to reduce the rate of multiplication. Factors that affect the environmental resistance are a) Physical b) nutritional, c) host plant and d) biotic.
a) Physical factors

i) Temperature – influence the rate of development and level of distribution – zone of effective temperature – aestivation – hibernation.
ii) Light – Certain life stages respond to light – photoperiodicity,
iii) Moisture – influence distribution and development,
iv) Climate –average physical conditions in a locality – influence rate and development.

b) Nutritional factors

i) Availability of food regulate population abundance.
ii) kind and quality of food influence life cycle.
iii) Host selection – monophagous, polyphagous – chemical factors in host selection.

c) Host Plant associated factors – rapidity of growth, foliage characteristics, taste factors etc.
d) Biotic factors

i) Competition – within and among different species (Inter and intra specific).
ii) Parasites and predators parasites like fungi, bacteria, protozoo, nematodes and various arthropods – predators like birds, mammals, reptiles, amphibions and insects check the population.
iii) Human population trend – Rapidly growing world population – growth rate projected world population – Indian population – resources.

Biotic factor

• Biotic factors of the environment tend to modify the activities of insects. Individuals within a population enter into varied interactions with each other besides interacting with the adjacent population. These interactions may be positive (or) negative according to whether it produces beneficial or harmful effects on the interacting individual (or) population. In the positive interaction, the individuals live adjusting with each other (Mutusalim, commensalisms). The negative interaction leads to competition, parasitism and predation.
i. Competition

• The active demand by two or more individuals of the same species of population. (Intra specific competition) (or) members of two or more species at the same trophic level (Inter specific competition) for a common resource (or) requirement that is actually limiting. Both intra specific and inter specific competition contribute to the density and diversity of a population.
a) Inter specific competition

• Two competing species can’t exist in a same place for a long time. Inter specific competiton leads to competitive displacement. (eg) Mediterranian fruit fly in Hawai in 1940. The accidental introduction of oriental fruit fly replaces the Mediterranian fruit fly. Competitive displacement between Nosema apis and mite Acarapis woodi in Honeybee. Tribolium(red flour beetle) eliminate oryzalphilus (saw toothed beetle) both are grown in same flour.
b) Intra specific competition

• If the common resource is abundance, no problem in the individual and if it is limited competition occurs and superior abilities will survive in the end. (eg) a)Aphid – dispersal. b) Cannibolsim in American bollworm, Helicoverpa armigera.
ii. Parasites and predator

• Interaction between predator and prey are different from the parasite and host relationship in that the predator and prey maintain an equilibrium more dynamic than the parasite and its hosts. The parasites in general, when the rate of parasitization is high cause death and resultant elimination of the hosts. But a predator never eliminates the prey completely. Parasite includes fungi, bacteria, protozoa nematodes and other arthropods. Predator includes insect predators, birds, mammals, reptiles, amphibians that check the population.
Abiotic factor (physical factors)
a) Temperature

• It has got a profound influence on the life cycle of insects. a) Temperature influences on the rate of development (or) number of generation (eg) Temperature is an important factor in the life of the bed bugs. The number of generations passed through during a year is directly dependent on the ambient temperature. As many as twelve generations occurs in the tropical and two in cold climate. For the sugarcane stem borer, Chilo infuscatellus, the larval period extend over 16-24 days in summer and 141-171 days in winter. b) Temperature influences the fecundity and rate of egg production. (eg) Cabbage Diamond backmoth lay more number of eggs at 18° C (larval temperature) than 22°C. c) Temperature influences the rate of migration and dispersal. (eg) In Desert lowest (Schistioceva gregaria), migration of swarms occurs at 17°C to 20°C.
• Zone of effective temperature. Normal life activities go on smoothly at a specific temperature (or) at a specific range of temperature. This is called the optimum temperature. The rate of chemical reaction within tissues is modified by temperature. Metabolic processes are influenced by temperature and increase with it upto a maximum and suddly decline at the upper lethal temperature. The extreme temperature alters the insect and the insect entes into diapauses (resting stage). If the resting stage is due to low temperature, than it is called hibernation. If the resting stage is due to high temperature, it is called Aestivation.
b) Light

• The radiant energy, termed light is one of the most important ecological factors affecting many aspects of the insect life. Several vital phenomena of the insect biology (eg) feeding, growth, development, diapuse, survival and ethology are profoundly influenced by light. Photoperiodism: Daily and seasonal duration of light has profound effect on the production of sexual form in Aphids. Short day length is influencing sexual forms, while long day length is influencing asexual forms (parthenogenetic) viviparous reproduction. Photoperiods also influence growth, metabolism and daily rhythm of activity (feeding, flying, mating and oviposition). The light influences on the inception and completion of diapauses.
• Daily rhythm of activity: It has been observed that many species of insects are not equally active throughout the 24 hr of the day. Some are primarily nocturnal (dark active); other are diurnal (day active) and still other which are referred to as crepuscular (dusk active) are active mainly at dawn and dusk.
c. Relative humidity

• Termites are a group of insects for which atmospheric humidity is an important ecological factor. They usually move towards a zone of high humidity, when subjected to the slightest desiccation. Humidity is high, rice brown plant hopper multiplication is more. Certain entomogenous fungi requires very high humidity for multiplication and spread (eg) white halo fungus, Verticillum lecanii attack on coffee green bug.
d. Rainfall

• For normal emergence of adults rainfall is a must (also it is essential for pupation) for insect like cutworms, Helicoverpa armigiera, Spodoptetra litura. If it is excess, grubs like white grubs will come out of environment where they are subject to predation. Excess rainfall control aphids and Diamond backmoth.
e. Wind

• It helps more in the dispersal of insect species besides interfering with their normal feeding, mating and multiplication. (eg) with the help of wind current Helicorerpa adult moth fly upto 90 km. Another examples is the spreads of eriophyid mite in coconut.
f.Soil type

• Type of soil play a role in multiplication of insects. (eg) wireworms multiply even in heavy clay soil (poor drainage) with lesser drainage, Whereas white grub multiply very well in loose sandy soil (light) with better drainage.
g)Water

• Standing (stagnated) water helps in multiplication of insect like mosquitoes. Running streams are preferred by black flies and caddish flies.
h) Tropographic factors

• Besides mountain, large areas under water viz., sea etc also act as physical for the spread of the insect.
Ecology related terminology

i. Habitat is the place where the organism lives.
ii. Population denotes groups of individuals of any kind of organism. Insect populations are groups of individuals set in a frame that is limited in time and space.
iii. Community in the ecological sense includes all the populations of a given area. Community can also be defined as interacting ‘web’ of populations where individuals in a population feed upon and in turn are fed upon by individuals of other populations (Fig. 1)

iv. Ecosystem

• • Ecosystem or ecological system is the functioning together of community and the nonliving environment where continuous exchange of matter and energy takes place.
• • In other words ecosystem is the assemblage of elements, communities and physical environment.
• • Ecosystem is the ultimate unit for study in ecology as they are composed of living organisms and the nonliving environment.
• Examples of natural ecosystem: Ponds, lakes and forests ecosystem (Fig.2)
v. Biosphere is the term used for all of the earth’s ecosystems functioning together on the global scale.

Living Genes Cells Organs Organisms Populations Communities components

+

Nonliving components Matter Energy Biosphere

= Biosystems

• Gene Cell Organ Organism Population Ecosystem
• Figure 3. Flow of matter and energy in an ecosystem
Agro ecosystem is largely created and maintained to satisfy human wants or needs. It is not a natural ecosystem but is man made. Agro ecosystem is the basic unit of pest management - a branch of applied ecology.
A typical agroecosysyetm (Fig. 4) is composed of

i. more or less uniform crop-plant population
ii. Weed communities
iii. Animal communities (including insects)
iv. Microbiotic communities
v. and the physical environment the react with.

Unique features of Agroecosystem

• Dominated by plants selected by man
• No species diversity and no intraspecific diversity. Genetically uniform
• Phenological events like germination, flowering occur simultaneously
• Lack of temporal continuity - due to various agricultural operations carried out by man like ploughing, weeding, pesticide application etc.
• Plants contain imported genetic material
• Nutrients are added
• Outbreak of pests, weeds and diseases occur frequently