Insect egg deposition induces Pinus sylvestris to attract egg parasitoids
Monika Hilker1,*,
Carsten Kobs1,
Martti Varama2 and
Kai Schrank1
1 Institut für Biologie, Freie Universität Berlin, Haderslebener Strasse 9, D-12163 Berlin, Germany and
2 Finnish Forest Research Institute, Vantaa Research Centre, PO Box 18, FIN-01301 Vantaa, Finland
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Fig. 1. (A) A female Diprion pini laying eggs on a pine needle. Eggs are laid sequentially in a row (mass) of approximately 10–20 eggs and are covered by a greenish secretion. (B) Cross section through a needle of Pinus sylvestris bearing an egg deposition of the sawfly D. pini. The ovipositing female slits the needle with her ovipositor valves starting at the epidermis (E) of one edge of the needle (arrow) and then cutting the parenchyma (Pa), the endodermis (En), the transfusion tissue (Tr) and one of the vascular bundles (V). After removal of the plant tissue, an egg is placed inside the needle. Ch, egg chorion with oviduct secretion; Y, egg yolk. Finally, the eggs are covered by a secretion (C) from an abdominal gland. Staining with Astrablau (Aldrich, Germany) and Safranin T (Fluka, Germany). Light micrograph. Scale bar, 0.43 mm.
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Fig. 2. Induction of plant synomones by egg deposition. Responses of egg parasitoid female Chrysonotomyia ruforum to volatiles from differently treated (A–D) twigs of Pinus sylvestris offered in a test field (T) consisting of a four-arm olfactometer with three control fields supplied with clean air (1, 2 and 3). Mean values for the time the parasitoid females spent walking in the test and control fields are given over an observation period of 600 s. Values are means + S.D. The dashed line is the mean time if the duration of walking had been equal in the test and control fields. *** indicates a significant (P<0.001) and NS a non-significant (P>0.05) difference evaluated by a Friedman ANOVA. Different letters indicate significant (P<0.05) differences evaluated by the Wilcoxon–Wilcox test.
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Fig. 3. Mechanism of synomone induction. Responses of egg parasitoid female Chrysonotomyia ruforum to volatiles released from differently treated (A–C) twigs of Pinus sylvestris offered in a test field (T) consisting of a four-arm olfactometer with three control fields supplied with clean air (1, 2 and 3). Mean values for the time the parasitoid females spent walking in the test and control fields are given over an observation period of 600 s. Values are means + S.D. The dashed line is the mean time if the duration of walking had been equal in the test and control fields. *** indicates a significant (P<0.001) and NS a non-significant (P>0.05) difference evaluated by a Friedman ANOVA. Different letters indicate significant (P<0.05) differences evaluated by the Wilcoxon–Wilcox test.
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Fig. 4. Role of jasmonic acid in synomone induction. Responses of egg parasitoid female Chrysonotomyia ruforum to volatiles released from a twig of Pinus sylvestris treated with (A) an aqueous Tween solution of jasmonic acid and (B) an aqueous Tween solution only as a control. Volatiles from the twigs were offered in a test field (T) consisting of a four-arm olfactometer with three control fields supplied with clean air (1, 2 and 3). Mean values for the time the parasitoid females spent walking in the test and control fields are given over an observation period of 600 s. Values are means + S.D. The dashed line is the mean time if the duration of walking had been equal in test and control fields. ** indicates a significant (P<0.01) and NS a non-significant (P>0.05) difference evaluated by a Friedman ANOVA. Different letters indicate significant (P<0.05) differences evaluated by the Wilcoxon–Wilcox test.
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© The Company of Biologists Ltd 2002
