Gonatopus bartletti, Olmi, 1984, Olmi, 1984

Guglielmino, A., Bückle, C. & Moya-Raygoza, G., 2006, Description of the larval instars of Gonatopus bartletti Olmi, 1984 (Hymenoptera: Dryinidae), Zootaxa 1226 (1), pp. 51-60 : 52-55

The postembryonic development of G. bartletti includes four larval instars: three immature and one mature instar.

Egg ( Figs 1–3 )

Eggs (Figs 2,3) are small, kidney­shaped, smooth, with little brown area at their anterior pole and without conspicuous structures on their surface when observed with optical microscope. At hatching, chorion is ruptured, breaking into pieces; fragments remain attached to cuticle of larva in some cases.

Remarks. Females of Gonatopus bartletti parasitize adults of Dalbulus maidis , laying their eggs into the intersegmental membranes of the host’s abdomen ( Fig. 1 ).

First instar ( Fig. 4 )

Length: 0.50–0.60 mm; width: 0.34–0.46mm.

Larva very small, with two anterior white kidney­shaped cephalic vesicles. Colour changing from whitish at hatching to light brown; posterior body region only slightly bent in ventral direction and protruding outside the host; body with ventral tubercle ( Fig. 4 ), probably serving to anchor parasite in host’s body (see Barret et al. 1965).

Indistinct segmentation present ( Fig. 4 ); respiratory system has nine (one thoracic and eight abdominal) pairs of lateral spiracles.

Remarks. After the larva has completed its growth, it moults and its exuvia remains attached to the body of the following instar, as in other species of Gonatopodinae .

Second instar ( Fig. 5 )

Length: 0.68–0.90 mm; width: 0.42–0.60mm.

Remarks. This instar differs from the first one by an increase in size, a sturdy integument and the presence of the first instar exuvia ( Fig. 5 ).

Third instar ( Fig. 6 )

Length: 0.92–1.16 mm; width: 0.48–0.58mm.

Remarks. The main characters distinguishing this instar from the previous ones are its size and the presence of two exuviae (relating to 1 st and 2 nd instar), which cover it partially ( Fig. 6 ).

Mature larva ( Figs 7–22 )

Length: 1.64–3.44 mm; width: 0.80–0.96 mm.

Larva apodous, creamy white yellowish, with typical facies of mature Gonatopodinae larvae.

Head capsule longer than wide, well sclerotized with its posterior part retracted under 1 st thoracic segment ( Fig.14 ). Antennae very simple, reduced to two small elliptical pits, both with two small conical sensilla medially ( Figs 15 , 22 ); one sensory bristle present medially to each antenna ( Fig. 22 ). Near base of each mandible is peculiar subrectangular heavily sclerotized and dark pigmented area, with lens­shaped quite transparent protuberance in its anterolateral angle (its ultrastructure and function are under investigation) ( Figs 9 , 16 , 22 ); one pair of small sensory pores and one sensory bristle present in each of those areas ( Fig. 22 ). Fronto­clypeal suture indistinct. Fronto­clypeus with one pair of sensory pores and two pairs of sensory bristles ( Figs 14 , 22 ); anterior margin of clypeus concave. Labrum large, dorsally convex, apically rounded. On its dorsal surface, from proximal to distal margin, one pair of sensory pores, row of 7–8 sensory bristles placed semicircularly in preapical position, and numerous irregularly distributed apical sensory bristles ( Figs 14, 17 , 18 , 22 ). Epipharynx without peculiar structures. Mandible strongly sclerotized, unidentate ( Fig.22 ). Each mandible with broad base, narrow and medially curved apical portion and dorsal subproximal sensory bristle. Maxilla ( Fig. 18 ) weakly sclerotized, each with maxillary palpus, three sensory bristles arranged in semicircle near base of palpus and two other ones placed ventrolaterally in its proximal region. Maxillary palpi subcylindrical ( Figs 18, 19 ). Each palpus with apical area delimitated by cuticular edge with four sensilla of different size and shape: two uniarticulated, small and cone­shaped and two bi­articulated consisting of long cylindrical basal and small cone­shaped apical article; in subapical position one medially placed sensory bristle and laterally large sensory pit present ( Fig. 19 ). Labium weakly sclerotized, consisting of postmentum and the median lobe ( Figs 18, 20 ). The median lobe, formed by prementum and hypopharynx ( Buyckx, 1948), bears spinneret distally and labial palpi subapically. Three pairs of sensory bristles are arranged in semicircle in proximity of base of each palpus. Labial palpi ( Fig. 21 ) broad and well defined, similar in structure to maxillary palpi, each with proximal large sensorial pit and four distal sensilla structurally similar to those of maxillary palpi. The spinneret opens apically by transverse slit ( Fig. 20 ).

Thorax and abdomen with indistinct segmentation ( Figs 7, 8 ), with some sparse minute bristles. Tracheal system with nine pairs of spiracles (one pair of large thoracic spiracles and eight pairs of small abdominal ones located on first eight abdominal segments) ( Figs 8 , 12, 13 ).

Remarks. The mature larva feeds on the internal organs of the host. Having killed the host, the larva emerges into the open and builds its cocoon in a suitable place, often on a maize leaf ( Fig. 11 ). The whitish subovoidal cocoon consists of a double wall ( Fig. 10 ).

Figures

FIGURE 22. Mature larva of Gonatopus bartletti: Head, dorsal view. Scale bar = 0.1mm.

FIGURES 1–6. Gonatopus bartletti Olmi, eggs and immature larvae. 1. Dalbulus maidis (Delong & Wolcott) adult, with Gonatopus­eggs in its abdomen. 2. High magnification detail of 1: eggs inserted in host abdomen. 3. Eggs, laid on the internal side of host abdomen sclerites. 4. First larval instar, lateral view. 5. Second larval instar, lateral view. 6. Third larval instar, lateral view. CV = cephalic vesicles; X1 = exuvia of first instar; X2 = exuvia of second instar; VT = ventral tubercle.

FIGURES 7–11. Gonatopus bartletti Olmi, mature larva and cocoon. 7. Mature larva emerging from its host Dalbulus maidis (Delong & Wolcott). 8. Mature larva, lateral view. 9. Dark pigmented area near the base of mandible. 10. Cocoon. 11. Cocoon on a maize leaf.

FIGURES 12–17. Gonatopus bartletti Olmi, SEM microphotographs of the mature larva. 12. Thoracic spiracle. 13. Abdominal spiracle. 14. Head, dorsal view. 15. Antenna. 16. Dark pigmented area near the base of mandible showing the hemispheric protuberance, dorsal view. 17. Clypeus and labrum, dorsal view.

FIGURES 18–21. Gonatopus bartletti Olmi, SEM microphotographs of the mature larva. 18. Head, ventrolateral view. 19. Maxillary palpus, lateral view. 20. Spinneret, ventrodistal view. 21. Labial palpus, distal view.