11
Rice Brown Planthopper
no role in regulating JH during developmental stage of the insect. However, the gene
encoding for FAMeT had a positive change in female adults revealing that the enzyme
might be playing an important role in reproductive functions like ovary development,
vitellogenesis or egg yolk production etc. (Liu et al., 2010). Genetically, brachyptery
is a sex linked character clearly controlled by a single pair of dominant alleles in the
females but the segregation was not so clear in males of BPH (Iwanaga et al., 1985).
Evolutionary and adaptive significance of morphoforms in BPH:
Presence of high RH in the environment is very crucial for growth and multiplication
of BPH in rice ecosystem. To achieve this they appeared to have evolved the ability
of long range migration as a solution. Therefore macropterous forms have come into
existence to facilitate the process. It is of common knowledge that whenever there are
adverse conditions in rice ecosystem higher proportion of macropterous forms develops
to get away from the adversity. It could be unfavourable food usually rich in sugars
and poor in free aminoacids, peptides and proteins or higher temperatures or very low
temperatures where BPH cannot survive or multiply.
Usually with the beginning of senescence of rice crop food quality is poor. So BPH
has to leave the crop in search of a more nutritive young crop where it can thrive and
multiply for at least few generations. Evolution of macroptery and brachyptery appear
to have far higher significance to BPH than mere migration to a favourable place of
good food availability.
Deeper significance of BPH morphoforms than mere migration to favorable
area:
If we critically observe the type of climate that exists in rice growing tropical countries,
usually during rainy season favorable temperature exists at the beginning of the season.
Almost similar temperature conditions exist throughout that season. So temperature
is not the limiting factor for growth and multiplication of BPH during rainy season or
kharif season. When macropterous adults settle in young crop, the nymphs of the next
generation emerge within a span of 15-20 days. Then, those first instar nymphs start
feeding on nutritively rich rice plants. So, that itself forms the point where almost all
of those nymphs will become brachypterous adults by release of high titre of JH III in
the system of first instars. Simultaneously gene transcripts responsible for continued
maintenance of the same higher concentration of JH III till the penultimate nymphal
