Egg Parasitoids in Cereal Crops Ecosystem

Abstract

The major targets of egg parasitoids occurring in cereal crops include mainly stem borers (Scirpophaga, Chilo), leaf folders (Cnaphalocrocis), the gall midge and leaf/plant hopper. Among trichogrammatids commonly occurring in cereal ecosystem are the ‘minutum’ group (T. chilotraeae, T. pretiosum, T. chilonis) and the ‘japonicum’ group (T. japonicum, T. pallidiventris). The other families of egg parasitoids include Scelionidae, Mymaridae, Eulophidae and Platygasteridae. In rice ecosystem, especially on Scirpophaga incertulas, Trichogramma, Telenomus and Tetrastichus species appear to complement in natural biocontrol. Platygaster oryzae is the important and only egg-larval parasitoid on rice gall midge, while on leaf and plant hoppers, Anagrus and Gonatocerus (Mymaridae), besides Oligosita (Trichogrammatidae), are the more common egg parasitoids. Trials on inundative release of T. japonicum and T. chilonis have shown positive impact on yellow stem borer and leaf folder in rice. Scope for in situ conservation of egg parasitoid through utilising alternate host plants as reservoir hosts exists in rice ecosystem. Future research thrust areas include more efficient use of Tetrastichus and Telenomus against rice stem borer and Platygaster against gall midge, besides ecological studies on tritrophic interactions and role of crop varieties towards improved integration.

Appendix I: Taxonomic Keys to the Identification of Egg Parasitoids Prevailing in Cereal Ecosystem

1	Front wing different from the hindwing in size, shape and venation, and as long as or slightly beyond tip of abdomen at rest, hamuli present; with or without cross veins in the four membranous wings; wing scales absent; veins M and Cu not multibranched; fontanelle absent; antenna usually elbowed, clubbed or filiform; tarsi 3–5 segmented (Hymenoptera-2)
2(1)	Hind tibia with 1 or 2 spurs (absent in a few Ichneumonidae), but none modified for pruning; sometimes a dense brush of enlarged hairs developed on the basitarsus and apex of tibia 3
3(2)	Pronotum with at least a lateral spiracle cover lobe reaching back to tegula, or, if wingless, lobe margined with close fine hairs; lateral pronotum vertically grooved for reception of fore femora 4
3′	Pronotum not reaching back to tegula (almost so in some Leucospidinae, in which tegula is lengthened, and in some Mymaridae); forewing with venation very reduced, without fully formed cells; pronotum separated from tegula by prepectus14
4(3)	Spiracle cover lobe of pronotum without close fine hairs along its margin5
5(4)	Lateral pronotum vertically grooved for reception of front femora, scutellar cup absent, costal cell present or absent 6
6(5)	Costal cells present, or venation greatly reduced; hindwing without closed cells7
7(6)	Mid- and hind tibia with only 1 spur8
8(7)	Venation absent or reduced to submarginal vein with a slightly knobbed apex, egg-larval parasites of Orseolia oryzae (Platygasteridae)9
8′	Forewing with distinct though sometimes short marginal and stigmal veins (Scelionidae)10
9(8)	Antennal scape and legs light orange-yellow; apical four antennal segments pale brown, broad, and subquadrate, basal four smaller in size (length and width) than apical segments and light orange-yellow; coxae yellow except brown coxa I; lateral posterior part of thorax with dense greyish pubescence. Platygaster oryzae Cameron
10(8′)	Gaster with lateral margins rounded; wide latero-tergites of metasoma loosely attached to sternite (not incised) forming no depressed submarginal ridge; 2nd tergite (T2) of metasoma the longest; antenna 12 segmented in male and 10–11 in the female (Telenominae)11
10′	Gaster with lateral margins carinated; wide latero-tergites incised to form impressed submarginal ridge; metasoma usually subequally segmented with 3rd segment (T3) often the longest; lateral ocelli usually nearer to the inner orbits than to median cells (Scelioninae)
11(10)	Frons smooth and shining, lack sculpturing in the lower half of frons, eyes usually hairy; parapsidal furrows absent 12
12(11)	Hosts- stem borer eggs 13
13(12)	Small telenomines, body length 0.5–1.1 mm (Telenomus sp.)
14(3′)	Tarsi three segmented (Trichogrammatidae) 15
14′	Tarsi 4 or 5 segmented 25
15(14)	Antennal club of female one segmented; funicle two segmented; marginal vein curved distally away from anterior borders of front wings to extend up to stigmal vein; setae of disc usually in vein tracks16
15′	Antennal club of female with more than one segment23
16(15)	Antennal club of male three segmented bearing two funicular segments; vein track of radial sector (RS1) absent; forewing with long marginal fringe; stigmal vein elongate (Trichogrammatidae)
16′	Antennal club of male one segmented with unsegmented flagellum but with 2 slightly constrictions below in the region of funicular segments; forewing with short marginal fringe; vein track RS1present (Trichogramma)17
17(16′)	Median ventral projection absent or inconspicuous 18
17′	Median ventral projection present 20
18	Dorsal expansion of gonobase horseshoe-shaped basally; fringe of forewings one-fifth width of wings; aedeagus distinctly longer than apodeme, both together as long as or longer than tibia III 19
19(18)	Ovipositor slightly exerted, longer than tibia III which is as long as aedeagus with short arm; male genitalia elongate ovate, chelate structure in line with MVP; thoracic venter of female never white; antennal hairs of male long, the longest 3.5 times maximum width of flagella Trichogramma japonicum Ashmead
20(17′)	Antennal hairs moderately long, longest hair 2–2.5 times maximum width of flagellum 21
21(20)	Longest antennal hair 2.5 times maximum width of flagellum22
22(21)	Antennal flagella of male with less than 35–40 hairs; dorsal expansion of fonobase with narrow lateral lobes basally; small median ventral projection sharp, ovate to long ovate; apodeme as long as aedeagus, together shorter than tibia III; ovipositor longer than tibia III Trichogramma chilonis Ishii
23(15′)	Marginal fringe of forewing at least half maximum with width; discal ciliation usually in rows but sparse; female antenna two segmented (ring and funicle) (Oligosita)
23′	Forewing with a narrow smoky or brownish tinge across wing beneath stigmal vein; scape as long as combined lengths of pedicel and funicle; gaster pale yellow except tergites latero-dorsally dark brown Paracentrobia yasumatsui Subba Rao
23″	Forewing with a rounded brown tinge below stigmal vein; scape a little longer than combined length of pedicel and funicle; tergites I-IV of abdomen uniformly brown Paracentrobia andoi Ishii
24(23)	Marginal fringe of forewings one-third or one-half the maximum width of wings(25)
25(14′)	Basal part of hindwing reduced to thread like stalk composed of the sub-marginal vein; wing disc ribbon-like; forewing with a long marginal fringe; antennal sockets wide apart (Mymaridae) 26
25′	Hind wind never stalk-like basally 28
26(25)	Gaster with more or less distinct petiole, convexly rounded or subglobular basally; mesopostphragma not projecting into the gaster; tarsi 4 or 5 segmented27
26′	Gaster broadly connected to the propodeum (hind part of thorax); mesopostphragma plainly projecting into gaster; a pair of distinctly separated plates (=postscutellum) behind scutellum; antennae 9 segmented in the females (6 funicular segments, solid club) and 13 segmented in the males; tarsi 4 segmented (Anagrus)
27(26)	Tarsi five segmented28
28(25′&27)	Petiole short, wider than long; antennae of male 13 segmented and female 11 segmented, with 8 funicular segments); marginal vein not elongated, venation not reaching basal one-third of wing; gaster subsessile (Gonatocerus spp.)
28′	Tarsi four segmented 29
29 (30′)	Hind coxa not greatly enlarged, if so, not compressed or disc like and with different pattern; hind tibia without diamond like arrangement of bristles; gaster distinctly constricted at the junction with the propodeum 30 (Eulophidae)
30(29)	Forewing with interruption between submarginal vein and parastigma; tarsus usually four segmented (Eulophidae) 31
31(30)	Notaular line complete; axillae angularly produced; scutellum with two longitudinal submedian grooves; pronotum without cross-carina; middle lobe of mesoscutum with hairs, median area never bare, usually with a median groove; malar sulcus present; stigmal vein long; funicle three segmented in female 32
32 (31)	Oriental species; body shining green with bluish lustre to uniformly brownish black or pale yellow33
33 (32)	Body uniformly brownish black with greenish reflections in the head and thorax; legs whitish yellow except brownish coxa I and femur I; antenna blackish brown except yellow-brown scape, funicular segments not slender; cub of male antenna black, broad and much wider than any antennal segment Tetrastichus howardi Olliff
33′	Body metallic blue or shining green with bluish lustre; antenna brown except yellow scape with brown sensoriae in male; legs yellow except greenish coxae I and IV; ocelli in a low triangle, front ocellus never reached by scape; thorax smooth and shining abdomen elongate, pointed behind with a slightly exerted ovipositor; female antenna 3 equally long funicular segments 3 times as long as broad; male; 1st funicular segment smaller than the rest, funicle and club clothed with short hairs, sensorial organ of scape narrow and elongate and nearly as long as scape; abdomen ovoid of scape narrow and elongate and nearly as long as scape; abdomen ovoid, slightly longer than thorax Tetrastichus schoenobii Ferriere
33″	Very similar to T. schoenobii; shiny green with bluish lustre; legs uniformly whitish yellow with dark brown last tarsal segments; three equally long funicular segments only twice longer than broad; abdomen narrow and pointed behind, ovipositor more exerted than in T. schoenobii (pupal parasite of Hydrellia philippina-Tetrastichus sp.)

1. Adapted from Barrion and Litsinger (1994)