Abstract:
The bug had five
nymphal instars with average nymphal period of 22.2, 25.0 and 23.5 days on
soybean, cowpea and mash, respectively. Its duration was significantly short on
soybean compared to that recorded on other two hosts. Total life cycle was
completed in 29.75 days on soybean, 34 days on cowpea and 33 days on mash. Among the three hosts, the bug survived for significantly longer duration
on soybean. Morphometrics
of different developmental stages of the bug was also recorded. Female (2.59mm  1.13mm) was
found to be bigger in size compared to male (2.32mm 0.79mm). Biological
parameters of the bug were studied on soybean, cowpea and black gram under laboratory conditions (temp 23-30°C
and RH 67-90%).

Keywords: Biology, Chauliops choprai,
soybean, cowpea and mash.

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Introduction

 

 

Materials and
methods

Maintenance of the stock in the laboratory

Stock culture of the bean bug was maintained
separately on potted plants of three hosts viz., soybean (Him Soya), cowpea
(C 475) and black gram (Him Mash-1) under caged conditions in Department of
Entomology throughout the course of this study. For this purpose, the copulating
adults (Plate1.)
of bean bug were collected from naturally infested plants of soybean, cowpea
and black gram grown under field conditions and released on potted plants of
respective crops maintained separately under caged conditions in the lab. The
insects were allowed to feed and multiply on the potted plants. Dried and
matured plants were periodically replaced with young plants of the same
varieties. Various stages of the insect required for the experimentation were
obtained from the stock culture and for their feeding fresh leaves of different
hosts were obtained from the field.

Biology of C. choprai on three hosts
under lab conditions

            Biology
of the bug was studied on three hosts viz.,
soybean (cv. Him Soya), cowpea (cv. C 475) and mash (cv. Him Mash1) under
laboratory conditions following methodology of earlier workers (Sharma and
Sharma 1998) with some modifications. During the period of experimentation
daily averages of temperature and RH were recorded with the help of Thermo
Hygro Clock TM-2 (Mextech TM). For the purpose of recording data on
various biological parameters of C.
choprai, experiments were conducted in complete randomized design with three
hosts (soybean, cowpea and mash) taken as treatments and number of individuals
(eggs, nymphs and adults of the bug) kept for recording observations were taken
as replications. The observations were recorded on 100 individuals (in batches)
for studying different biological parameters. Data were recorded on the
following parameters of the biology of the bug:

       
i.           
Incubation period

     
ii.           
Duration of nymphal instars

    iii.           
Total nymphal period

    iv.           
Total life cycle

     
v.           
Morphometrics of the developmental stages

    vi.           
Pre-oviposition, oviposition and post
oviposition period

  vii.           
Fecundity

viii.           
Adult longevity

i) Incubation period: To know the
incubation period, freshly laid eggs of C.
choprai were taken from the stock culture along with leaves and placed in
Petri dishes (7.5cm in diameter) at the rate of 25 per Petri dish. To prevent
the desiccation of eggs, Petri dishes were provided with a moist filter paper
at the bottom. The experiment was repeated 4 times, thus, a total of 100 eggs
(25 eggs/ replication) were observed on each host. The eggs were observed daily
in order to record data and to determine incubation period and per cent
hatching. The period between date of oviposition and date of hatching was
considered to be the incubation period.

ii) Duration of
nymphal instars: After hatching, first instar nymphs were shifted to specimen jars (54cm) with tender leaves of host crops. Fresh leaves were provided as food
daily until adult stage. In order to know the nymphal period each first instar
nymphs were kept in individual jar containing fresh leaves for
further rearing. Stalks of the leaves were wrapped with moist cotton wool to
keep the leaf turgid. Moist filter paper was kept at the bottom of the jar to
maintain humidity and the mouth of the jar was covered with muslin cloth for
proper aeration. Moulting periods and dead nymphs were recorded daily in order
to determine the developmental periods and survival rates of each stage. Different
instars were determined on the basis of their exuvae. The duration of first
instar nymph was taken as the time period between nymphal emergence and first
moulting. The duration of other instars were taken as the time period between
two successive moults. Time gap between hatching of eggs and last nymphal
moulting was taken as the total nymphal period.

iii) Pre-oviposition, oviposition and post
oviposition period: After completion of
nymphal duration, adults emerged at the same day were transferred to glass chimneys
(2015cm) for the purpose
of mating under laboratory conditions on all the three host crops, separately. The number of eggs laid on the plants by
adults were counted daily. The pre-oviposition, oviposition and post
oviposition periods were recorded separately. The period between the emergence
of adult female bug to the start of egg laying was recorded as the
pre-oviposition period. The time taken from initiation of egg laying to the
last egg laid by the female was considered as the oviposition period.
Post-oviposition period was taken as the time period between the last egg
laying and death of female. Number of eggs laid by each female was recorded to
determine its fecundity. Number of females dying on each day of their life was
recorded to determine age specific morality. The effect of each host on
the oviposition of the bug was recorded.

iv) Adult longevity:
The data on longevity of male and female, total fecundity of the bug were
recorded. The adult longevity was
recorded for both the sexes separately. The number of days the adult survived
was taken as the adult longevity.

Morphometrics of
different developmental stages

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