Ecacanthothrips Bagnall

Okajima, Shûji & Masumoto, Masami, 2024, The genus Hoplandrothrips and its relatives (Thysanoptera: Phlaeothripidae) from Southeast Asia and Taiwan, Zootaxa 5489 (1), pp. 22-91 : 25-26

Ecacanthothrips Bagnall

Ecacanthothrips Bagnall, 1909: 348 . Type-species: Acanthothrips sanguineus Bagnall (synonymised with Idolothrips tibialis Ashmead by Palmer & Mound, 1978), by monotypy.

The genus Ecacanthothrips shares most generic features with Hoplandrothrips , and seems to be distinguished only by the larger number of sense cones on antennal segment III. Ecacanthothrips species have more than six (usually more than 10) stout sense cones on the relatively enlarged antennal segment III (cf. Fig. 113 ), and this is the only autapomorphy mentioned for this genus. There is usually a larger number of sense cones on the ventral surface of the segment than on the dorsal surface. Two Ecacanthothrips species from Japan, E. inarmatus and E. moundi , usually have about 10 sense cones (cf. Fig. 104 ), but infrequently have six or seven sense cones in small individuals. In particular, E. coniger from Borneo and Peninsular Malaysia has more than 60 dark sense cones even in small individuals ( Fig. 88 ). In contrast, Hoplandrothrips species usually have three rather slender sense cones on that segment. Even in Hoplandrothrips , however, a widespread species, H. flavipes , as well as four species described from Japan and one new species described below from Taiwan have four rather stout sense cones on that segment. Moreover, E. andrei from Indonesia, Peninsular Malaysia and Thailand has four or five, but rarely two or three, sense cones on a rather slender segment III ( Fig. 59 ), although it is included undoubtedly in the tibialis species-group of Ecacanthothrips . Members of this species-group include not only the widespread type-species of the genus, E. tibialis , but also E. claricornis from the Philippines and Sulawesi, Indonesia, all have a median tubercle on the inner margin of the fore femur in both sexes ( Okajima 1983). Furthermore, Hoplandrothrips quinqueconus sp. n. from Taiwan newly described below, unusually has five (rarely six) sense cones and may be closely related to H. ryukyuensis from the Ryukyu Islands. Therefore, the difference of sense cone number seems not to satisfactorily distinguish these two genera, and the genus Ecacanthothrips could well be treated as an Oriental species-group of the worldwide genus Hoplandrothrips , as suggested by Okajima (2006). However, there is an essential morphological difference in these sense cones on antennal segment III between E. andrei and Hoplandrothrips species. In E. andrei the sense cones are comparatively small and all arise unusually on the ventral apex of the segment (see Fig. 5 in Palmer et al. 1978), but those of Hoplandrothrips species, including species with four or five sense cones on that segment, have the sense cones rather large and with one or two usually arising on the inner apex, and two, rarely one or three, on the outer apex of the segment. Frequently, the outer one is placed ventrally, but such a condition is widely found in the Phlaeothripidae . Even in H. flavipes , the formation of the four sense cones is not so different from ‘usual position’ as Fig. 104A in Okajima (2006). It appears that there is a qualitative difference between the sense cones, even if the number is the same or reversed. Thus, it might be interpreted that the sense cones on antennal segment III of E. andrei are not homologous with those of Hoplandrothrips species, or at least no evidence is found that they are homologous. In comparative morphology, it is very important to verify structural homology by evaluating relative positional relationships. This qualitative difference could probably be explained by the fact that the common ancestor of E. andrei and E. claricornis had at least as many sense cones as in E. claricornis which is undoubtedly most closely related to E. andrei , then those sense cones have been reduced in number in E. andrei , but not conspicuously changed in E. claricornis . Therefore, these two genera, Ecacanthothrips and Hoplandrothrips , are both retained tentatively in the present study. However, this is only a temporary treatment and an arbitrary distortion. Even if the homology of the sense cones in both genera is rejected, it will not immediately lead to a clear separation between these two genera and the relationship between them remains insufficiently clarified. In comparison with some of the synapomorphies shared by these two genera, the autapomorphy involving the sense cones of Ecacanthothrips presumably has only a limited phylogenetic significance. We consider that Hoplandrothrips should be a synonym for Ecacanthothrips , but there are problems with Hoplandrothrips that need to be resolved, so we will not express that formally at this time. One problem is the relationship between Hoplandrothrips and Malacothrips , which might also be considered as a single genus, as discussed below under Hoplandrothrips . Moreover, Hoplandrothrips , includes at least 130 species, and repeated nomenclatural changes can cause taxonomic confusion. Incidentally, Malacothrips is the oldest name among these three genera. In addition, Ecacanthothrips is considered to be sister group to the Hoplandrothrips ryukyuensis - group (see below under H. flavipes ), and it is probably not so closely related to the flavipes -group (see below under H. coloratus ) as was previously considered.

Among the 11 described species, andrei , claricornis and tibialis , are included in the tibialis -group, with the head rather longer, a median tubercle on the inner margin of fore femur in both sexes, and the fore coxa strongly extruded postero-externally in large males. Four species, inarmatus , leai , moundi and nigellus , are included in the inarmatus -group, with a rather long head and unarmed median inner margin of fore femur. Two species, spinipes and tenuicornis , may also be included in the inarmatus -group, but the relationships of the remaining two species, coniger and kolibaci are unclear. It is noticeable that in all species belonging to these two groups, most of the sense cones are on the ventral rather than the dorsal surface of antennal segment III. E. coniger is peculiar in having antennal segment III strongly distorted ( Fig. 88 ) with numerous stout sense cones which are situated asymmetrically, biased antero-externally, also the mouth cone is extremely long and pointed ( Fig. 91 ) and extending beyond the prospinasternum. However, most other character states are similar to those of inarmatus -group. E. kolibaci , based on two females from Sichuan, China, has the head short and four stout sense cones on antennal segment III. According to the original description ( Pelikan 2000), most of these four thick sense cones are ventral on the large antennal segment III, and the species is here retained in this genus with some hesitation. The species has not been available for this study and further observations are needed. Especially in the inarmatus -group, each species shows confusing size related variation as well as geographical variation, and it is very difficult to discriminate each species.

In this paper, 12 Oriental Ecacanthothrips species are recognised in this genus, including E. brevicornis sp. n., here newly described from Bali Is., Indonesia.

Diagnosis. Small to medium sized species, usually macropterous. Most features very similar to those of Hoplandrothrips , but with the following differences: antennal segment III usually enlarged (not enlarged in andrei and brevicornis ), much wider than segment IV, with more than six sense cones (usually more than 10) and if fewer, then mostly on ventral apex of the segment; fore femur often with a median tubercle or tooth on inner surface in addition to a pair of apical tubercles in both sexes.

Figures

FIGURES 111–119. Ecacanthothrips nigellus, female. (111) fore leg; (112) head and prothorax; (113) antennal segments II– VIII; (114) antennal segment III, dorsal view; (115) antennal segment III, ventral view; (116) metanotum and pelta; (117) prosternum and mesopresternum; (118) sub-basal wing setae; (119) tube.

FIGURES 102–110. Ecacanthothrips moundi. (102) Head and prothorax, female; (103) head and prothorax, large male; (104) antennal segments III–IV, female; (105) metanotum, female; (106) pelta, female; (107) fore leg, large male; (108) fore leg, female; (109) sub-basal wing setae, female; (110) tube, female.

FIGURES 84–92. Ecacanthothrips coniger. (84) Head and prothorax, female; (85) fore leg, female; (86) head and prothorax, large male; (87) antenna, female; (88) antennal segments III–V, female; (89) metanotum and pelta, female; (90) sub-basal wing setae, female; (91) prosternum and mesopresternum, female; (92) tube, female.

FIGURES 56–64. Ecacanthothrips andrei. (56) Head and prothorax, female; (57) head and prothorax, large male; (58) antenna, female; (59) antennal segments III–V, female; (60) metanotum and pelta, female; (61) prosternum and mesopresternum, female; (62) hind femur, female; (63) sub-basal wing setae, female; (64) tube, female.

FIGURES 1–14. Ecacanthothrips species. E. andrei 1–2: (1) female; (2) large male. E. brevicornis sp. n. 3–4: (3) female; (4) male. E. claricornis 5–6: (5) female; (6) large male. E. coniger 7–8: (7) female; (8) large male. E. leai 9–11: (9) female; (10) large male; (11) small male. E. moundi 12–13: (12) fmale; (13) large male. E. nigellus: (14) female.