Oviposition behaviour of Gryon gallardoi (Hym. Scelionidae) on eggs of Spartocera dentiventris (Hem. Coreidae)

RESUMO

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 25 + or -1C/12 h photophase till hatching. The mean number of parasitized eggs was 7.8 + or - 0.81 (IMG01 + or - 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 + or -imes per female. In nearly all of these events, parasitism was unsuccessful. Walking and resting were observed less frequently than the other behaviours (1.6 + or - 0.56 and 2.1 + or 0.48 times/female, respectively). Superparasitism occurred on average 3.6 + or - 0.88 times per egg mass, with 2.7 + or - 0.57 eggs being superparasitized. Among these, on average 87.4 + or - 5.37 percent led to successful development of an adult parasitoid. The average time spent on the each kind of oviposition behaviour was 1.5 + or - 0.57 min for drumming, 3.9 + or - 0.56 min for ovipositor insertion and 0.4 + or - 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 percent) occurred in the longitudinal extremities of the egg. In average 31.1 + or - 7.21 percent 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