Lophodiplosis trifida Gagné, an Australian gall midge on paperbark, Melaleuca quinquenervia (Myrtaceae), is a recent release in southern Florida for the biological control of that host. The larval stage is described for the first time and compared to that of other Lophodiplosis species. Photos of galls and illustrations of larvae are provided. Second and third instars of L. trifida are unusual among Cecidomyiidae for the lack of setae on most papillae.
Lophodiplosis trifida Gagné has been successfully introduced into southern Florida to aid in the control of paperbark, Melaleuca quinquenervia (Myrtaceae) (P. D. Pratt, unpublished). This insect was initially described as one of 5 Lophodiplosis species reared from Melaleuca spp. in the vicinity of Townsville, Qld., Australia (Gagné et al. 1997). No further species has been added to Lophodiplosis and, except for L. trifida in Florida, the genus is still known only from eastern Australia. The other 4 species, Lophodiplosis bidentata Gagné, Lophodiplosis cornuata Gagné, Lophodiplosis indentata Gagné, and Lophodiplosis denticulata Gagné, were taken from separate and distinctive galls of paperbark. Lophodiplosis trifida was initially thought to be an inquiline in galls of 3 of the other species because it was reared in association with them but not associated with any particular distinctive gall of its own (Gagné et al. 1997). Subsequent observations in the vicinity of Brisbane, Qld., showed that L. trifida forms separate, often very prominent galls (Figs. 1–4) in young shoots (Purcell et al. 2007). In the earlier situation in Townsville, stem galls of L. trifida galls were evidently inconspicuous, perhaps containing only 1 or 2 larvae, and had presumably been masked by galls of the other Lophodiplosis species and associated plant tissue in rearing cages. The larval stage of L. trifida was not described initially, unlike those of 3 of the other species of Lophodiplosis (that of L. denticulata remains undescribed). Now that L. trifida has taken on biological control importance, we take this opportunity to describe the instars for future identification.
MATERIALS AND METHODS
Larvae of known L. trifida, as determined from adults and pupae reared in quarantine in Ft. Lauderdale, FL, were removed from paperbark shoot galls in various stages of growth. Specimens were the progeny, many generations removed, of material originally sent from Indooroopilly, Qld., Australia. Specimens were placed on slides for viewing in accordance with the method outlined in Gagné (1989). Other specimens were critical-point dried and placed on SEM stubs. Terminology for larval morphology follows that in Gagné (1989).
Length, 1.3–2.0 mm (n = 10). Body cylindrical, spindleform. Head capsule hemispherical, with apodemes as long as capsule; antennae short, as long as wide. Spiracles present on prothorax and on first through eighth abdominal segments. Integument with horizontal rows of minute spicules ventrally on anterior third of 2nd and 3rd thoracic and all abdominal segments, remainder smooth if not weakly and irregularly lined. Spatula (Figs. 6, 11) widest posteriorly when fully sclerotized, with long shaft, anteriorly with 2 large, triangular teeth and a shorter tooth between. Full complement of papillae present except only 2 pairs on terminal segment, 1 corniform, the other seti-form. Setae present on 2 of 3 of each of the 4 groups of lateral papillae and on 1 of the pairs of terminal papillae.
Second Instar (Figs. 13–14)
Length, 0.6–0.9 mm (n = 10). Body shape, head, spiracles, integument and papillae as for third instar. Spatula present, short, the acutely triangular anterior tooth up to half length of shaft. As with third instar, full complement of papillae is present except for 2 pairs on terminal segment and setae present on only 2 of 3 of each of the 4 groups of lateral papillae and on 1 pair of terminal papillae.
First Instar (Fig. 15)
Length, 0.3–0.5 mm (n = 10). Body shape, head, and integument as for second and third instars. Spiracles present only on prothorax and eighth abdominal segment. Spatula absent. Presence of papillae as for second and third instars except that pleural and dorsal papillae and the non-setose pair of terminal papillae of second and third instars all with minute seta.
Comments on Larval Stage of L. trifida
The first and second instars of this species are unusual among Cecidomyiidae for the almost complete absence of papillar setae. Setae occur on only 2 papillae in each of the 4 sets of lateral triplets and on 2 terminal papillae. The first instar, on the other hand, has tiny setae, no longer than the diameter of their papillae, on all pleural and dorsal papillae, in addition to the setae already mentioned for the third and second instars. The only other example known of the lack of papillar setae generally is the genus Caryomyia, a North American genus, in which most of species completely lack papillar setae, even those on the lateral and terminal papillae (Gagné 2008). The integument is remarkably smooth in L. trifida, with the anteroventral horizontal bands of spicules the only sculpturing.
The 5 species originally placed in Lophodiplosis come from simple to complex galls of Melaleuca spp. (Gagné et al. 1997). These species are an eclectic mix that, besides having a host genus in common, share the distinguishing pupal character of vertexal extensions that are evidently used in cutting through gall tissue prior to adult emergence. Many gall midges have variously shaped prominences on the head for that purpose, but they are almost always extensions of the antennal bases, not of the vertex. Larvae of Lophodiplosis are diverse, but this is not unusual in genera with a variety of gall shapes (Gagné 2008). Larvae of L. trifida are unique in Lophodiplosis for the lack of setae on most papillae, their long, narrow, tridentate spatula in the third instar, and mostly smooth integument. The other species of Lophodiplosis for which larvae are known, L. bidentata Gagné, L. cornuata Gagné, and L. indentata Gagné, have short setae on most papillae, a short, wide, bidentate spatula, and a rugose integument. The type species, L. indentata, and L. trifida both have only 4 papillae on the terminal segment, but all 4 papillae have setae on L. indentata while only 2 have setae on L. trifida. Both species have a spatula in the second instar. In gall midges, a second instar spatula occurs only in some gall-making genera where it seems to have arisen de novo in each of the genera where it appears (Gagné 2008).
We thank P. Malikul for making the slide preparations, Scott D. Whittaker, SEM Laboratory Manager, Smithsonian Institution for assistance with the scanning electron microscope, Diana Marquez for electronically arranging the photos and drawings onto plates, and James A. Lollis and Elizabeth D. Mattison for assistance in collecting galls and larvae, and the South Florida Water Management District for financial support to this project. We are grateful also to Keith M. Harris, Woking, Surrey, United Kingdom, David A. Nickle and Allen L. Norrbom, Systematic Entomology Laboratory, and 2 anonymous reviewers for critical comments on the manuscript.