9750 J. Agric. Food Chem., Vol. 54, No. 26, 2006
Upadhyay et al.
coupling constant of 12 Hz, and were assinged to two methines adjacent
to oxygen in the molecule. The carbons carrying oxygen were observed
at δ63.39 and 70.19 in the 13C NMR spectrum. Also, there was a triplet
at δ2.33 integrating for two protons and was assigned to R-methylene
significance of potency estimation, g value, indicated that the
mean value is within the limits at all probabilities (90, 95, and
99%) as it is less than 0.5. Values of the t ratio greater than
1.96 indicated that the regression was significant. The steep
slope values indicated that even small increase in the dose causes
high mortality. Values of the heterogeneity factor less than 1.0
denoted that in the replicate test of random samples, the doses
response lines would fall within 95% confidence limits and thus
the model fits the data adequately.
1
protons to the carbonyl group. Its H NMR also displayed a multiplet
at δ5.34 for the two olefinic protons. Also, there was a multiplet at
δ1.29 integrating for six protons and it corresponded to three methylenes
in the molecule. All of this spectral data showed compound CDF1 to
contain an unsaturated six-membered lactone ring and was therefore
assigned constitution as 6-(1-hydroxy-non-3-enyl)tetrahydropyran-
2-one.
When the newly emerged adult insects of B. chinensis were
exposed to sublethal doses of different extracts and compounds,
they laid a lesser number of eggs, as comparison to the control,
i.e., when no extract or compound was used (Tables 3 and 4).
The maximum percent oviposition deterrence index (%ODI (
SE) at highest sublethal doses was observed in the case of CD1
(45.11 ( 1.92) followed in decreasing order by CD2 (41.18 (
2.43), CD3 (39.98 ( 1.78), and CD7 (30.88 ( 1.82), respec-
tively. When the insects were exposed to sublethal doses of
pure compounds obtained from the extract CD1, the maximum
oviposition deterrence index was observed for C2 (46.73 ( 2.73)
followed by C1 (45.56 ( 1.65). F values at df 3 and 20 were
highly significant for all stimuluses at all probability levels (90,
95, and 99%) indicating that all stimuli affected the oviposition
behavior of the pest. CDF1 has also shown oviposition inhibition
in B. chinensis. The maximum %ODI (69.73 ( 1.103) has been
recorded for CDF1 (Table 4).
The proposed structure was also biogenetically feasible as it could
have been possibly derived from 5Z,8Z-tetradecadienoic acid, commonly
known as goshuyic acid. Selective epoxidation of the double bond at
the C-5 position of the acid, followed by epoxide ring opening and
subsequent lactonization with the loss of a water molecule, can lead to
the formation of CDF1. Thus, from correlating spectral studies and
plausible biogenesis pathways, the structure of CDF1 was proposed as
6-(1-hydroxy-non-3-enyl)tetrahydropyran-2-one.
6-(1-Hydroxy-non-3-enyl)tetrahydropyran-2-one (CDF1). Color-
less oil; gave a single spot on TLC, Rf ) 0.7 in chloroform. IR νmax
(KBr): 3427, 2920, 2852, 1744, 1463, 1377, 1164, 1099, 721 cm-1
.
1H NMR (δ, CDCl3, 300 MHz): 0.96 (t, 3H, H-10′), 1.29-1.33 (6H,
-CH2), 1.96 (m, 2H, allylic -CH2), 2.33 (t, 2H, -CH2CO-), 2.77 (m,
2H, H-3′), 4.13 (dd, 1H, J ) 4.3 and 12 Hz, H-2′), 4.28 (dd, 1H, J )
6.2 and 12 Hz, H-1′), 5.34 (m, 2H, dCH). 13C NMR (δ, CDCl3, 75.47
MHz): 14.45, 23.05, 25.23, 29.50, 29.64, 30.06, 31.94, 32.29, 34.43,
63.39, 70.19, 129.37, 131.51, 176.24. EIMS m/z (%): 240 (M+, 14),
213 (10), 202 (14), 186 (20), 170 (15), 158 (22), 141 (30), 127 (18),
111 (32), 99 (44), 97 (56), 85 (64), 71 (100), 43 (30).
The above study showed clearly that different extracts as well
as the compounds isolated from C. decidua can significantly
kill or influence the egg delivery response of B. chinensis. This
also indicated that insects have susceptibility and oviposition
deterrency to biochemical extracts and compounds of C.
decidua, which can be used for the disruption of egg lying in
the field and stored grain godowns to reduce the pest population.
Bioassay Protocol. The toxicity of different extracts and compounds
isolated from it was tested against B. chinensis. Ten adult insects were
taken from laboratory culture and placed in glass culture tubes (10 cm
ht. × 4 cm diameter) along with ten grains of gram. Filter paper strips
(1 cm2) treated with different doses of extracts/pure compounds,
dissolved in their concerned solvents, were then placed at the bottom
of the culture tubes, and the open end was closed by the cotton sheet.
The coated filter paper strip with either the extract or the compound
was air-dried before application. In control, the filter paper strip was
treated only with the solvent used for dissolving extract/pure compound.
For each fraction and compound, four different doses were used, and
for each dose, six replicates were set. Mortality was recorded after 24,
48, 72, and 96 h.
Furthermore, isolation and characterization of some other
minor components of the rest of extracts of C. decidua will
certainly provide complete insight into the total pesticidal
activity of C. decidua and will help in the preparation of
formulations against the pulse beetle B. chinensis in future.
The oviposition inhibition assay was studied by repeating the above
procedure. For each chemical stimulus, three different doses were used,
and for each dose, six replicates were set. The number of eggs laid
was recorded after 96 h.
Data Analysis. The LC50 values were calculated by POLO program
(27). The efficacy of the test stimuli was compared with control on
the basis of oviposition deterrence index (ODI). The ODI of females
for the test stimuli was calculated as 100(A - B)/(A + B), where A
and B are the number of eggs laid in the control and in the test,
respectively. One-way analysis of variance was performed between
different doses of stimulus and number of eggs laid (28).
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RESULTS AND DISCUSSION
The extracts CD1, CD2, and CD3 were quite effective at
lower doses while CD7 was effective at higher doses. The LC50
values for different extracts at different exposure periods are
given in Table 1. From extract CD1, two compounds, namely,
triacontanol (C1) and 2-carboxy-1,1-dimethylpyrrolidine (C2),
have been isolated and were found to be toxic for the adult
insects (Table 2). The LC50 values at different exposure periods
were found to be lower for C1 as compared to C2.
A novel compound, CDF1, isolated from fraction CD7, has
also shown insecticidal activity. The mortality rate was found
to increase with an increase in dose, and the LC50 values
decreased at different graded exposure periods indicating that
the response was dose- and time-dependent. The index of