Studies on Conura torvina (Hymenoptera: Chalcididae) Reproduction and biology in Relation to Hosts in Brassica Crops.
Conura torvina (Cresson)
(Hymenoptera: Chalcididae) is a
solitary pupal endoparasite of
numerous insect species. In
Brassica crops it acts as a
parasite of Plutella xylostella (L.)
(Lepidoptera: Plutellidae) and
was found as a hyperparasite of
Cotesia rubecula (Marshall)
(Hymenoptera: Braconidae) and
several other parasitoid species.
Cotesia rubecula was introduced
into Virginia in 1987 as a
biological control agent for Pieris
rapae (L.) (Lepidoptera:
Pieridae), and because C.
torvina was thought to have
eliminated this population of C.
rubecula, studies of C. torvina¹s
reproductive biology and
behavior were initiated. A study
using plants laden with "trap
hosts" to detect C. torvina
activity in the spring indicated no
activity until late June, but
proved trap host sampling to be
an efficient and effective method
of monitoring C. torvina activity.
Studies of C. torvina¹s ability to
reproduce in C. rubecula pupae
of different ages indicated that C.
torvina can successfully
parasitize pupae at all stages of
development, but was most
successful in young to middle
aged pupae. Studies of C.
torvina¹s host species preference
indicated the larger host species
such as P. xylostella were
preferred. Equal numbers of P.
xylostella and C. rubecula were
parasitized, but a greater
proportion of fertile eggs were
laid in P. xylostella. Smaller host
species were often ignored. Host
dissection studies indicated that
caged C. torvina were inefficient
at host finding and oviposition.
Superparasitism was common,
but declined as the females
gained oviposition experience.
Experienced C. torvina
produced an average of 8.25
progenies per day for a period of
12 days when provided with 13
P. xylostella hosts each day.
Conura torvina produced up to
14 progenies a day when
provided 3 26 hosts. Dissection
of C. torvina ovaries indicated
three ovarioles per ovary with a
mean of 9.2 and maximum of 15
mature eggs per female. Host
dissection indicated that a mean
of 18 and maximum of 30 eggs
could be laid per day. New eggs
were produced as oviposition
occurred. Significantly larger
eggs were laid in P. xylostella
than in C. rubecula, and
significantly more eggs were laid
in C. rubecula than in P.
xylostella. From these data and
data from earlier studies I
concluded that C. torvina has a
poor reproductive ability and its
impact as a hyperparasite is
limited to the summer months.
This makes C. torvina an unlikely
cause of C. rubecula¹s
Advisor:Dr. L. T. Kok; Dr. R. L. Pienkowski; Dr. D. G. Pfeiffer; Dr. R. D. Fell; Dr. B. D. Opell
School:Virginia Polytechnic Institute and State University
School Location:USA - Virginia
Source Type:Master's Thesis
Date of Publication:01/24/1997