Insect pest life cycle stages face unfavarable conditions

1. DIAPAUSE
Mango
Nut
Weevil
White Grub
Bombyx mori
Grasshopper
Locust
Pink bollworm
Cabbage butterfly
Red hairy caterpillar
By:
Vijendra Jagrat

2.  The word diapause was coined by Wheeler
 It is the period of arrested growth or development in the life cycle of
the insects during which the physiological processes like differentiation
and reproduction are suspended. Diapause is represented by low rate of
metabolism, low oxygen consumption, low body weight, low body water
content and vitamin deficiency in the blood.
 Diapause may occur in egg, larva, nymph, pupa or adult stage.
Examples:
1. Egg (embryonic) diapause - Bombyx mori, Grasshoppers, Locusts
2. Larval diapause- Pink bollworm (Pectinophora gossypiella)
3. Pupal diapause- Red hairy caterpillar (Amsacta albistriga) , Cabbage
butterfly (Pieris sp.)
4. Adult diapause- Mango nut weevil (Sternochaetus mangiferae), White
Grub, Fruit flies

3. Types of diapauses: two types
1. Obligatory diapause: It refers to the stage of suspended activity of the insect which
is a hereditary character controlled by genes and is species specific. e.g. egg
diapause in silkworm
2. Facultative diapause: It is the stage of suspended activity of the insect due to
unfavourable conditions and with the onset of favourable condition, the insect
regains its original activity. e.g. Cotton pink bollworm, Pectinophora gossypiella
The unfavourable conditions may be biotic or abiotic. Biotic conditions are natural
enemies, population density etc. whereas abiotic conditions are temperature,
rainfall, humidity, photoperiod, type of food material etc.
The occurrence of diapause during summer due to high temperatures is
known as "aestivation" where as the period of inactivity during winter due
to low temperature is known as "hibernation".

4. There are five phases in diapauses
i) Induction phase
ii) Preparation phase
iii) Initiation phase
iv) Maintenance phase
v) Termination phase
Photoperiod is the most important stimulus
initiating diapause.

5. Facultative diapause Obligate diapause
Most common Rare
Occurs only when induced by
environmental conditions
Occurs in specific life stage in
every generation regardless of
environmental conditions.
Termination of diapause occurs
by Token stimuli (viz. chilling,
sunlight, water etc.)
Termination of diapause occurs
spontaneously without any
external stimuli.
e.g. Multivoltine insects e.g. Univoltine insects
Fraenkel (1959) proposed “THE TOKEN STIMULI THEORY

6. Environmental factors
that trigger diapause
1. Photoperiod is the alternating phases of light and dark in the day or
the ratio of day-to-night length, known as the photoperiod. Seasonal
changes to the photoperiod (such as shorter days as winter approaches)
are the major factors responsible for the start or end of diapause for many
insects
2. Temperature - Some insects require specific thermal requirement to end
the diapause phase. For example, the woolly bear caterpillar must
endure a period of chilling to trigger the end of diapause and continuation
of the life cycle
3. Food As the growing season ends, the diminishing quality of their food
sources may help trigger a diapause phase in some insect species. As
French bean plants turn brown and dry the balck bean bug adults will
enter a state of diapause
Long days and high temperature induces diapause e.g Bombyx mori
Black Bean Bug

7. Diapause Quiescence
It is highly evolved form of dormancy
for overcoming cyclic and extreme
environmental conditions
Development is temporarily inhibited
by unfavourable environment
It is long adaptive form of dormancy It is for short period of time
Stage is determined (Egg or larva or
pupa or adult)
Stage is not determined
Diapause is irreversible dormancy
(larva entering diapause will be
changed to pupa) and the insects are
called heterodynamic insects.
Quiescence is reversible dormancy
(quiescent larva will come out as larva
insects are called homodynamic
insects
Pupa of Helicoverpa armigera
 Trehalose is present in overwintering insects. It acts as a cryoprotectant.
 Glucose is present in desiccating insects.