INFLUENCE OF TEMPERATURE ON THE FUNCTIONAL RESPONSE OF Dinarmus basalis (HYMENOPTERA: PTEROMALIDAE), A PARASITOID OF Callosobruchus chinensis (COLEOPTERA: BRUCHIDAE)
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Abstract
Dinarmus basalis Rondani (Hymenoptera: Pteromalidae) is the larval-pupal ecto-parasitoid
of Callosobruchus chinensis Linnaeus (Coleoptera: Bruchidae). The functional response of
D. basalis parasitizing late larval and pre-pupal stage of C. chinensis was estimated over a
range of temperatures and host densities. A functional response equation was used in which a
quadratic component that included temperature was substituted for handling time. The
instantaneous search rate increased with increasing temperatures. A linear relationship
between the rate of parasitism and prey density was observed with r
2
values between 0.951
and 0.997. Plotting prey density against prey parasitized by four temperature levels of D.
basalis fit well with the type II Holling’s model. The rate of searching efficiency and
handling time were estimated 0.676 d
-1
and 0.010 day for 20°C temperature, 0.894d
-1
and
0.005 day for 25°C temperature, 0.975 d
-1 and 0.003 day for 30°C temperature, 0.798d
-1 and
0.007day for 35°C temperature, respectively. Thus, handling time decreased from lower
temperature to higher temperature except 35°C temperature. D. basalis effectively parasitized
C. chinensis at the temperature of 30°C. The functional response data, the model predicts a
maximum number of 333.33, 200, 142.86 and 100 C. chinensis were parasitized per day by
an individual at 30°C, 25°C, 35°C and 20°C temperature, respectively. In 30°C temperature
D. basalis parasitized the highest number of prey, followed by other temperature levels and
showed higher parasitism (95.73%) and suppression (97.44%) of C. chinensis populations
with 20 host density.