Egg parasitoids belonging to the family Trichogrammatidae are among the most widely used biological control agents in the field. Currently there are about 85 genera in the world (Viggiani, 2001), among which 26 have been recorded from India (Yousuf & Shafee, 1987). Of these, the genus Trichogramma Westwood, with about 250 species distributed across the world, is the most important one from the applied point of view. Trichogrammatoidea Girault, another important genus, has a much more restricted distribution than Trichogramma with only 24 species known so far, mainly from the southern hemisphere and the Oriental region.

In India, many species of Trichogrammaand Trichogrammatoidea (predominantly the former) have been used in applied / augmentative biological control programmes. The distinguishing characters between the two genera are summarized below.

Distinguishing features between Trichogramma and Trichogrammatoidea

Trichogramma Westwood	Trichogrammatoidea Girault
Vein track RS1 present	Vein track RS1 absent
Flagellum of male antenna unsegmented, with two slight constrictions below	Flagellum of male antenna five-segmented, with two funicular segments and a three-segmented club
Marginal fringe of setae short, not more than one-fifth the width of wing. Discal setae close, arranged in distinct rows	Marginal fringe of setae on fore wings distinctly much longer, measuring one-fourth to three-fourths the width of wing. Discal setae sparser and arranged irregularly
Male genitalia with dorsal expansion of gonobase of variable shape	Male genitalia without dorsal expansion of gonobase

Trichogrammatids used in augmentative biological control in India

• Trichogramma achaeae Nagaraja & Nagarkatti
• Trichogramma pretiosum Riley
• Trichogramma chilonis Ishii
• Trichogramma chilotraeae Nagaraja
• Trichogramma embryophagum Hartig
• Trichogramma japonicum Ashmead
• Trichogrammatoidea bactrae Nagaraja

Trichogramma achaeae Nagaraja & Nagarkatti

Adults 0.5 mm long and 0.15 mm wide across head. Males yellow with blackish sides of pronotum, mesonotum, mesopleurae, abdomen, hind coxae and femora. Antenna (Fig. 1) with long hairs, the longest being nearly 2.5x as wide as flagellum. Genitalia with prominent well-chitinized dorsal expansion of gonobase, which is subtriangular and apically blunt, nearly reaching tips of gonoforceps and sides of extruded portion being almost parallel (Fig. 4). Aedeagus (Fig. 3) about 1.5x as long as apodemes. Chelate structures (Fig. 5) in level with tips of gonoforceps. Minute protuberances present at base of chelate structures, one on either side of median ventral projection (Fig. 6), which is minute and inconspicuous.

Females similar to males when reared on same host and under same temperature conditions except for darker head. Antennae clubbed with few short hairs on flagellum.


Figs. 1-6. Trichogramma achaeae: 1. Male antenna, 2. Forewing, 3-6. Male genitalia: 3. Aedeagus, 4. Genital capsule, 5. Chelate structure, 6. Median ventral projection

 

India: Widely distributed. Russia. USA. West Indies.

Achaea janata (L.).

Trichogramma pretiosum Riley
Trichogramma brasiliense auctt.
Trichogramma brasiliensis auctt.

Male: Yellow with blackish mesoscutum and abdomen. Antennal hairs finely tapering and moderately long, the longest being 2.5x maximum width of flagellum. Trichiae arranged somewhat irregularly on forewing. Fringe on tornus of forewing about 1/6th width of wing. Male genitalia with DEG highly chitinised, triangular, basally constricted. CS far below level of tips of GF. MVP distinct, almost reaching level of CS. CR paired, extending anteriorly to about two-thirds length of genitalia. Aedeagus slightly longer than apodemes, both together distinctly shorter than hind tibia.

Female: Yellow with blackish anterior and posterior abdominal tergites. Antenna clubbed with few short hairs on flagellum. Ovipositor either slightly shorter than or equal to hind tibia.


Figs. 1-5. Trichogramma pretiosum: 1-4. Male genitalia: 1. Aedeagus, 2. Genital capsule, 3. Chelate structure, 4. Median ventral projection, 5. Relative lengths of aedeagus, hind tibia and ovipositor

Sugarcane borers.

 

The species introduced into India as Trichogramma brasiliense by the erstwhile Commonwealth Institute of Biological Control, Indian Station, in the late 1960s and '70s has been found to be T. pretiosum based on morphological evidence and hybridization / crossing studies. The original T.brasiliense is presently combined with Trichogrammatoidea as the type species has been found to belong to Trichogrammatoidea. Hence, the available Indian publications on T. brasiliense actually refer to T. pretiosum.

Trichogramma chilonis Ishii, 1941

Trichogramma chelonis Ishii
Trichogramma (Trichogramma) chilonis Ishii, 1941
Trichogramma chilones Ishii
Trichogramma confusum Viggiani, 1976

Figs. 1-5. Trichogramma chilonis: 1-4. Male genitalia: 1. Aedeagus, 2. Genital capsule, 3. Chelate structure, 4. Median ventral projection, 5. Relative lengths of aedeagus, hind tibia and ovipositor

Widely distributed almost throughout India. Widely distributed in the Oriental region. Pakistan, Bangladesh, Nepal, China, Malaysia, Indonesia, Philippines, Japan, South Africa, West Indies, Europe, USA, Hawaiian islands.

       
Trichogramma chilonis females on the eggs of Corcyra cephalonica (Stainton)

Several hosts have been recorded worldwide, primarily in Lepidoptera and also Diptera, Coleoptera, and Neuroptera. Some of the major pests against which it has been used / recorded in India include sugarcane borers (Chilo infuscatellus, Chilo sacchariphagus indicus, C. auricilius, Emmalocera depressella, Raphimetopus ablutellus, Acigona steniellus, Scirpophaga excerptalis), rice stemborer (Scirpophaga incertulas), leaffolder (Cnaphalocrocis medinalis), coconut blackheaded caterpillar (Opisina arenosella), diamondback moth (Plutella xylostella), and cotton bollworms (Earias vittella, E. insulana, Helicoverpa armigera, Pectinophora gossypiella).

This is perhaps the most widely used biological control agent in the field in Indian conditions, particularly on sugarcane.

Trichogramma chilotraeae Nagaraja & Nagarkatti

Adults 0.51 mm long and 0.2 mm wide across head. Males yellow with blackish pronotum, mesopleurae, mesoscutum, abdominal terga and hind coxae. Antennal flagellum unsegmented with long hairs, the longest being more than 3x maximum width of flagellum. Genitalia with more or less triangular dorsal expansion of gonobase, having a tapering apex which does not project beyond gonoforceps, but extends only to level of chelate structures. Aedeagus prominent and long, 1.2x as long as apodemes, projecting beyond gonoforceps (almost as long as or slightly longer than entire male genitalia). Large chelate structures located far below level of tips of gonoforceps. Protuberances at base of chelate structures very minute and inconspicuous. Median ventral projection very distinct and long, with two chitinous ridges extending anteriorly only for a short distance from median ventral projection. Aedeagus together with apodemes slightly shorter than hind tibia.



Figs. 1-2. Trichogramma chilotraeae: 1. Aedeagus, 2a&b. Male genitalia: 2. Genital capsule, 2a. Chelate structure, 2b. Median ventral projection

Females resemble males in colour, with the following differences: one or more penultimate abdominal tergites appear yellow in the middle and the anterior portion of mesoscutum is black. Antennae typically clubbed with few short hairs.

      Adults on the eggs of Corcyra

Chilo infuscatellus (Snellen).

India: West Bengal.

Trichogramma embryophagum (Hartig)

Encyrtus embryophagus Hartig, 1838
Ichneumon (Encyrtus) embryophagum (Hartig, 1838)
Ooencyrtus embryophagus (Hartig, 1838)
Trichogramma embryophagum (Hartig, 1838)

Pectinophora gossypiella, Sitotroga cerealella, Agrotis segetum, Opisina arenosella, Pieris brassicae, Corcyra cephalonica, Cydia pomonella. Complete list of hosts / associates can be found in the Universal Chalcidoidea Database (Online at http://internt.nhm.ac.uk/jdsml/perth/chalcidoids/).

         

Trichogramma japonicum Ashmead

Male: Dull yellow with thorax and abdominal tergites black. Antennal hairs long, sharply tapering, the longest being about 3.5x maximum width of flagellum. Fringe on tornus of forewing nearly one-fifth width of wing. Fringe on outer margin and tornus nearly equal in length. Genitalia with DEG highly sclerotized, horseshoe-shaped with blunt posterior extremity, sides of DEG extend slightly beyond sides of genitalia. CS far below the level of tips of GF. MVP inconspicuous, the entire region highly chitinised. CR paired, extending to about two-thirds length of genitalia. Aedeagus distinctly longer than apodemes, both together as long as or very slightly longer than hind tibia.

Female: Dull brownish yellow with black sclerites. Antenna clubbed with few short hairs on flagellum. Ovipositor nearly 1.5x as long as hind tibia.


Figs. 1-5. Trichogramma japonicum: 1-4. Male genitalia: 1. Aedeagus, 2. Genital capsule, 3. Chelate structure, 4. Median ventral projection, 5. Relative lengths of aedeagus, hind tibia and ovipositor

       Adults parasitising the eggs of C. cephalonica
    Adult on the egg mass of Scirpophaga incertulas (Walker)

Recorded on several 250 hosts worldwide. Some of the major pests of the Indian region parasitised by this species are Chilo partellus, C. infuscatellus, C. sacchariphagus indicus, C. suppressalis, C. auricilius, Cnaphalocrocis medinalis, Scirpophaga incertulas, S. excerptalis, Raphimetopus ablutellus, Leucinodes orbonalis, Helicoverpa armigera, and Plutella xylostella.

Recommended as part of BIPM packages in rice and sugarcane for the control of stem and tissue borers.

Trichogrammatoidea bactrae Nagaraja

Trichogrammatoidea bactrae fumata Nagaraja, 1979
Trichogrammatoidea bactrae bactrae Nagaraja, 1979
Trichogramma bactrae Nagaraja, 1979

Length 0.4-0.5 mm, width 0.15-0.18 mm. Head dull yellowish brown; eyes and ocelli red, antenna light brownish grey. Pro- and mesothorax, scutellum and metanotum dull yellowish brown to black Legs yellowish brown, mid- and hind femora greyish brown. Abdomen with tergites black, ventral side lighter. Antenna (Fig. 1) with flagellum about 1.75x as long as scape, with 22-26 long hairs, the longest being nearly 3x as wide as flagellum. Forewing (Fig. 2) as illustrated. Hind wing with fringe setae as long as in fore wing. Male genitalia (Fig. 4) narrow, nearly 3x as long as wide; apex and base indistinctly tapering, median cleft slightly less than a fifth of the length of genitalia; median ventral projection not conspicuous, lateral tubercles distinct, chelate structures (Fig. 5) large, slightly below level of gonoforceps. Aedeagus and apodemes of nearly equal length, aedeagus with apodemes nearly three-fifths the length of hind tibia. Female similar to male in general appearance, with ovipositor as long as hind tibia (Fig. 3).


Figs. 1-4. Trichogrammatoidea bactrae: 1. Male antenna, 2. Forewing, 3. Relative lengths of aedeagus, hind tibia and ovipositor, 4. Genital capsule, 5. Chelate structure

Throughout the Oriental region.

     
       Adults on Corcyra eggs

Lepidoptera: Bactra venosana Zeller, Pelopidas mathias (F.), Trichoplusia ni (Huebner), Agrius convolvuli (L.), Emmalocera depressella Swinh., Chilo infuscatellus Snellen, C. partellus (Swinhoe), Chilo sacchariphagus venosatus Walker, Helicoverpa armigera (Huebner) and several other hosts. Diptera: Sepedon sauteri Hend.

The eggs of rice moth, Corcyra cephalonica (Stainton), are used for the mass production of trichogrammatids in most of the commercial insectaries in India, though the eggs of Angoumois grain moth, Sitotroga cerealella (Olivier), are also used to a limited extent. Jalali et al. (2003) have given the detailed production procedure for C. cephalonica, with details on methods of field release, dosage, etc.