9
Rice Brown Planthopper
Involvement of hormones in morphoform development In BPH:
In BPH, JH plays a major role in morphoform development also apart from other
functions. Usually continuous maintenance of high titre of JH in nymphal stage leads
to development of the individual into brachypterous form while relatively low titre
of JH transfoms the individual to macropterous form. This in general is applicable to
both males and females although some differences have been observed in sexes with
regard to this phenomenon. But at what stage of nymphal development the individual’s
destiny is fixed to become brachypterous or macropterous and at what stage of
development it is possible to change the destiny of the individual insect by external
chemical interference is subject of present day research on this aspect. Intake of
Adequate quantity of nutritiously rich rice plant sap containing proteins, peptides and
free aminoacids by BPH in the first nymphal instar is more likely the most important
determining factor that fixes the individuals probability of becoming a brachypterous
adult. Exposure of the individual in 2- 4th instar to such a favourable food supply
appears to be having lower impact in destining the individual to a brachypterous adult.
This was observed by confining different nymphal stages to the most favourable food
or nutritious rice plants (Iwanaga and Tojo, 1986). However the ultimate destiny
of the individual can still vary up to 4th nymphal instar and certainly not in the 5th
instar or penultimate stage before becoming adult. This was demonstrated by external
application of JH to different nymphal instars of the insect (Wang et al., 1998). The fact
that Presence of JH above certain threshold in 5th instar nymphs is the deciding factor
to transform an individual insect to brachyptery was also proved by topical application
Plate 3: BPH first instar nymphs feeding on
rice leaf sheath, small 1mm in size
Plate 4: BPH eggs-translucent-cigar shaped-
inserted into leaf sheath in a row
