Orasema

Cameron, 1884

Species Guides

Orasema is a of chalcid wasps in the Eucharitidae containing at least 50 described . These are specialized of myrmicine ants (Formicidae: Myrmicinae), with documented including Pheidole, Wasmannia, and Solenopsis. The genus is widespread in the New World, ranging from northern Argentina to southern Canada. Several species groups have been established based on and molecular , with the stramineipes group being the most diverse. Some species have been associated with minor agricultural damage when ovipositing into crop plant leaves.

Orasema castilloae by (c) jcowles, some rights reserved (CC BY), uploaded by jcowles. Used under a CC-BY license.

Pronunciation

How to pronounce Orasema: //ɔːˈræsɪmə//

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Identification

Orasema are small chalcid wasps that can be distinguished from other Eucharitidae by their association with myrmicine and their characteristic involving planidial larvae. Species-level identification requires examination of morphological characters and reference to established species groups; keys are available for several revised groups including the coloradensis, bakeri, tolteca, sixaolae, acuminata, peraltai, johnsoni, and heacoxi groups. The stramineipes species group is the most diverse, containing 29 recognized species. Molecular data from 28S-D2 rDNA and oxidase I (COI) have been used in combination with to establish species concepts.

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Habitat

are closely tied to distributions and, for many , to plants bearing extrafloral . Orasema simulatrix has been documented in tree habitats where its host ant Pheidole desertorum is at night. Some species are associated with agricultural settings including tea plantations and banana, yerba mate, and blueberry .

Distribution

New World distribution ranging from northern Argentina to southern Canada. The stramineipes group shows greater diversity in tropical America compared to temperate regions. Documented distribution records include Argentina, Brazil, and the Caribbean (for O. minutissima). GBIF records indicate presence in Georgia, Indiana, and North Carolina in the United States, as well as Queensland, Australia.

Host Associations

Pheidole - Primary ; includes P. desertorum and undetermined in tea plantations
Wasmannia - W. auropunctata is for O. minutissima in the Caribbean
Solenopsis - S. saevissima-complex and fire ants in Argentina; for O. simplex
Formica - possible F. subnitens referenced but not directly confirmed
Chilopsis linearis - oviposition plantBignoniaceae; used by O. simulatrix for deposition near extrafloral

Life Cycle

Females deposit into incisions made on plant leaves, often in association with extrafloral . Eggs develop into minute first-instar larvae called . In O. assectator, eggs are laid singly in parallel rows on the underside of leaves. Planidia are concentrated in or on extrafloral nectaries (O. simulatrix) or exist as free-living larvae on leaf surfaces (O. assectator). access occurs when ants feed at nectaries; direct phoretic attachment to host ants has been rejected as the primary mechanism for O. simulatrix. Once in the nest, the planidium transfers to the last-instar ant larva and penetrates its body, remaining inactive until the host reaches the prepupal stage. Endoparasitic feeding begins at the prepupal stage; after host , the emerges and feeds ectoparasitically below the host through two additional instars, completely consuming host contents. Mature larvae pupate in the ant nest and are cared for by ants.

Behavior

employ a novel access mechanism: rather than using phoretic attachment to foraging ants or , they wait in extrafloral for host ants to feed, thereby gaining entry to the nest. In O. minutissima, two distinct size morphs are correlated with host use: a small morph attacks Wasmannia, while medium to large morphs attack different of Pheidole.

Ecological Role

of myrmicine ; potential of ant . May influence ant dynamics through host-specific .

Human Relevance

Some have been regarded as minor agricultural pests due to oviposition damage causing leaf scarring or secondary on banana, yerba mate, blueberry, and tea leaves. The 'sewing blight' of tea in Assam is caused by O. assectator and O. initiator oviposition in young leaves, producing brown spots and premature withering that affects tea quality. However, are rare and threats are usually temporary. O. minutissima has been identified as a potential agent for the Wasmannia auropunctata in areas outside its native Caribbean range.

Similar Taxa

Other Eucharitidae generaOrasema is distinguished from other Eucharitidae by its specialization on myrmicine ants; other may attack different or employ different access mechanisms
Orasema susanae-groupSister group to the stramineipes-group; mainly present in temperate regions of Argentina versus tropical distribution of stramineipes-group