Cornicle secretion by Aphis fabae affects the foraging behavior its parasitoid, Lysiphlebus fabarum
عنوان دوره: دومین کنگره بین المللی حشره شناسی ایران
نویسندگان
چکیده
Aphids use cornicle secretions to defend themselves against natural enemies, as does the black bean aphid, Aphis fabae Scopoli (Hemiptera: Aphididae) when attacked by its parasitoid, Lysiphlebus fabarum (Marshall) (Hym: Braconidae: Aphidiinae). In this study, we elicited cornicle secretions from aphids by gently stroking their thorax with a fine brush (= treated aphids), one hour before starting the experiment. The experimental arena consisted of a glass Petri dish containing a leaf disk of broad bean infested with 20 second instar A. fabae. Mated, two day-old L. fabarum females were singly introduced into arenas containing either treated or control aphids (n = 16 in both cases). Once a female encountered her first aphid, the lid of the dish was removed and she was observed continuously under a stereomicroscope for 30 minutes, during which time the onset and duration of all distinguishable behavioral events were recorded, including aphid defensive behaviors, such as kicking and secreting cornicle droplets. Wasps were faster (significantly accepted the patches) to attack their first aphid in patches of treated aphids (1.44 ± 0.17 vs. 2.12 ± 0.25 min.) (U=75.5, P=0.047). Wasps spent more time probing than in any other behavior, probed more control aphids (18.11 ± 0.89) than treated aphids (12.25 ± 1.01) (U=73.5, P=0.042), but spent more time probing treated aphids (14.95 ± 0.66 vs. 9.30 ± 0.63 min.) (U=16.0, P˂0.0001). Control aphids exhibited more frequent defensive behaviors than treated aphids, including kicking (F=42.3, df=30, P<0.0001), secreting cornicle droplets (F=57.8, df=30, P<0.0001), and raising and swiveling the body (F=12.3, df=30, P<0.001), a behavior often used to smear an attacker with cornicle secretions. This resulted in wasps spending more time grooming in treated arenas (5.18 ± 1.17 min.) than control ones (0.78 ± 0.22 min.) (U=35.0, P˂0.0001). These results reveal that cornicle secretion by A. fabae carries a cost in the form of reduced subsequent defensive behavior, and that L. fabarum females were responsive to aphid status (treated / control), adjusting their foraging behavior to the higher risk associated with attacking control aphids.
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