Ecologia Quimica

Journal of Chemical Ecology, Vol. 27, No. 1, 2001

RESPONSE OF THE LADYBIRD PARASITOID
Dinocampus coccinellae TO TOXIC ALKALOIDS FROM
THE SEVEN-SPOT LADYBIRD, Coccinella septempunctata

S. AL ABASSI,1 M. A. BIRKETT,2 J. PETTERSSON,1
J. A. PICKETT,2,* L. J. WADHAMS,2 and C. M. WOODCOCK2
1Department of Entomology
Swedish University of Agricultural Sciences
Box 7044, 750 07 Uppsala,Sweden
2Department of Biological and Ecological Chemistry
IACR-Rothamsted
Harpenden, Herts, AL5 2JQ. United Kingdom

(Received February 28, 2000; accepted August 27, 2000)
Abstract—Electrophysiological and behavioral responses of the ladybird
parasitoid Dinocampus coccinellae to volatiles from the seven-spot ladybird,
Coccinella septempunctata, were investigated to identify semiochemicalsinvolved in host location. Coupled gas chromatography–electroantennography
(GC-EAG) with D. coccinellae located a small peak of prominent activity in
an extract of volatiles from adult C. septempunctata. The active compound
was identified by coupled GC-mass spectrometry and by comparison with an
authentic sample as the free-base alkaloid precoccinelline, which forms part
of the toxic defenseof this ladybird. Behavioral studies in an olfactometer
showed that D. coccinellae was significantly attracted to the volatile extract
and also to the alkaloid. Myrrhine, a stereoisomer of precoccinelline found in
low amounts in C. septempunctata and in other ladybird species, was shown
to be electrophysiologically active and significantly attractive. Perception of
ladybird alkaloids by D.coccinellae is a rare example of toxicants acting as
aerially transmitted cues for interactions between the third and fourth trophic
levels.
Key Words—Seven-spot ladybird, Coccinella septempunctata, Coleoptera,
Coccinellidae, electroantennogram, behavior, Dinocampus coccinellae, Hymenoptera, Braconidae, alkaloid, precoccinelline, myrrhine, hippodamine,
volatile, semiochemical.

* To whomcorrespondence should be addressed. e-mail: john.pickett@bbsrc.ac.uk

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0098-0331/ 01/ 0100-0033$19.50/ 0  2001 Plenum Publishing Corporation

AL ABASSI

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ET AL.

INTRODUCTION

Ladybird beetles or ladybugs (Coleoptera: Coccinellidae) are important predators contributing to the natural control of pest aphid populations. However, they
are themselves attacked by a range of naturalenemies (Majerus, 1994). General predation on ladybirds by vertebrates such as birds is largely prevented
by highly toxic alkaloids contained in a reflex bleed released when the ladybird is attacked. The effectiveness of this chemical defense is enhanced by the
associated bright warning (aposematic) coloration and corelease of characteristic volatile compounds, e.g.,2-isopropyl-3-methoxypyrazine, which serves as a
protective allomone and also as an aggregation pheromone (Al Abassi et al.,
1998). The wasp Dinocampus coccinellae Schrank (Hymenoptera: Braconidae)
is the main parasitoid of a number of ladybird species and can cause substantial
reductions in populations of the seven-spot ladybird, Coccinella septempunctata L. (Majerus, 1994; Triltsch, 1996). There is a closeassociation with the
host, involving oviposition by D. coccinellae into the adult ladybird body and
subsequent larval development, which indicates a tolerance by the wasp to the
toxic alkaloids. Furthermore, D. coccinellae is known to utilize a combination
of visual and olfactory cues in short-range host location (Orr et al., 1992). Since
the associated semiochemicals may provide a means ofreducing the impact of
D. coccinellae on populations of C. septempunctata currently being exploited in
biological control programs, the antennal and behavioral responses of D. coccinellae to volatiles associated with C. septempunctata were investigated using
coupled gas chromatography–electroantennography (GC-EAG) and olfactometer studies. Our hypothesis was that D. coccinellae would exploit...