Brazilian Journal of Biology (Feb 2003)
Oviposition behaviour of Gryon gallardoi (Hym.; Scelionidae) on eggs of Spartocera dentiventris (Hem.; Coreidae)
Abstract
The oviposition behaviour of Gryon gallardoi (Hymenoptera; Scelionidae) on Spartocera dentiventris (Hemiptera; Coreidae) host eggs was investigated in the laboratory. Masses of 12 non-parasitized freshly laid (less than 24 h old) eggs were exposed to 2-5 days old mated females with previous oviposition experience (n = 10). Behaviour was observed for 2 h under the stereomicroscope. The eggs were Then kept individually at 25º ± 1ºC/12 h photophase till hatching. The mean number of parasitized eggs was 7.8 ± 0.81 (IMG01 ± SE). Five distinct kinds of behaviour were observed: drumming with antennae on the eggs, ovipositor insertion, egg marking, walking and resting. On average, ovipositor insertion was not followed by marking 4.3 ± 0.76 times per female. In nearly all of these events, parasitism was unsuccessful. Walking and resting were observed less frequently than the other behaviours (1.6 ± 0.56 and 2.1 ± 0.48 times/female, respectively). Superparasitism occurred on average 3.6 ± 0.88 times per egg mass, with 2.7 ± 0.57 eggs being superparasitized. Among these, on average 87.4 ± 5.37% led to successful development of an adult parasitoid. The average time spent on the each kind of oviposition behaviour was 1.5 ± 0.57 min for drumming, 3.9 ± 0.56 min for ovipositor insertion and 0.4 ± 0.06 min for marking. There was no significant variation on the duration of each behaviour as the parasitoid progressed in parasitizing an egg mass. Ovipositor insertion almost always (87.58%) occurred in the longitudinal extremities of the egg. In average 31.1 ± 7.21% of the individual emerging per egg mass were males, the larger proportion of males originating from the 2nd oviposition. The results show a range of oviposition behaviours common to the Scelionidae family. Egg marking behaviour was a good indicator of the effective oviposition by females. Superparasitism is only partially avoided, but its occurrence does not imply a failure of parasitoid emergence. The sex ratio is skewed towards females, and most males come from the first ovipositions.
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