Eucharitidae is the only family of insects known to specialize as parasitoids of ant
brood. Eggs are laid away from the host onto or in plant tissue, and the minute first-instars
(planidia) are responsible for gaining access to the host through some form of phoretic
attachment to the host ant or possibly through an intermediate host such as thrips.
Orasema simulatrix (Eucharitidae: Oraseminae) are shown to deposit their eggs into
incisions made on leaves of Chilopsis linearis (Bignoniaceae) in association with
extrafloral nectaries (EFN). Nectary condition varies from fluid-filled on the newest
leaves, to wet or dry nectaries on older leaves. Filled nectaries were about one third
as common as dry nectaries, but were three times as likely to have recent oviposition.
Larger numbers of undeveloped eggs, or eggs with mature planidia inside, were associated
with filled and wet EFN. For emerged planidia, the distribution was shifted from a
concentration at filled nectaries to an even greater concentration at wet nectaries.
More planidia were found in EFN (9.50 ±2.85) than outside EFN (1.00 ± 0.60). Planidia
were tested for their attachment to adult and larval ants and to adult and immature
thrips (potential intermediate host), but the results do not support simple attachment
as a viable means for transfer and successful parasitism. Pheidole desertorum was
identified as the host ant, and at night is the dominant ant in the tree canopy of
C. linearis. Feeding at the EFN by the host ant, and the direct association with planidia
near to or in the EFN, is interpreted as a novel means of accessing the host brood.