8
Rice Brown Planthopper
“hopper burn” if no control measures are adopted .
Regulation of morphoforms in BPH:
Generally proportion of macropterous or brachypterous adults developed from 5th
instar nymphs is influenced by many factors. Chemical composition of the rice plant
is the most important factor affecting the wing-form ratio of BPH. Among different
nymphal instars, supply of nutrients for 1st instar nymphs is important. Feeding of first
instars on plants with good nutrient status results in development of high proportion of
brachypterous adults Conversely, if first instars when allowed to feed on plants with
poor nutrition during vegetative stage due to lower nitrogenous fertilizer application
or on plants during senescence usually result in development of high proportion of
macropterous adults, both males and females. Temperature range of 21° to 27
℃
which
is optimal for nymphal development and adult reproduction for BPH is also favorable
for production of higher proportion of brachypterous forms. However, at temperatures
lower than 21
℃
or higher than 31
℃
higher proportion of macropterous forms result.
Relative humidity and population density are not related to wing dimorphism (Zhang,
1983). However, recent studies have revealed that irrespective of external factors that
promote macroptery or brachyptery, the whole process is under hormonal regulation
and genetically controlled.
Neurosecretory system in BPH:
A typical neurosecretory system in BPH consists of 1. Neurosecretory cells present
in the brain, 2. Corpora allata (CA) and corpora cardiac (CC) present in the head
region 3.Thorasic glands (TG) located in thorax which is typical to other insects. The
brain neurosecretory cells release a hormone usually termed as brain hormone (BH).
BH stimulates the production of juvenile hormone (JH) in CA and CC is involved in
storage and regulatory release of JH. BH also regulates the production and release of
moulting hormone or ecdysone (ED) from TG. In general JH has several functions in
insect physiological processes like growth, development, metamorphosis, reproduction
and also regulation of wing dimorphism. In BPH presence of JH above certain titre or
concentration in the insect body enable the individual to continue to remain in nymphal
stage while ED coordinates other functions related to the moulting process.
