6. General Ecology.
In considering the ecology of the Heteroptera no distinction will be made between indigenous and introduced species so long as the latter are established. The following scheme takes account of all species known to me, whether described or not, provided sufficient data are available to gauge their ecological position. The most important factor in the distribution of the Heteropters seems to be their relation to plants. This relation tends to be expressed rather in terms of flora than of vegetation: in other words, a bug is restricted to a group (whether order, family, or genus) of allied plants rather than to the plants of any given association or formation. For instance, a single species of Mirid of a pale-green colour marked with vivid red is attached both to the tree-fern Cyathea dealbata in the forest and to bracken-fern (Pteridium esculentum) in the open. Rhopalimorpha obscura affects grasses and sedges usually in clear country, but it also occurs on the latter when these plants fringe the course of a forest-stream. A species of Nysius occurring almost solely on Raoulia tenuicaulis, and abounding at elevations up to 4,000 ft., follows this plant in river-beds down to sea-level; but here we have a somewhat different case, since the new habitat obviously offers more points of ecological similarity than in the case of the fern-loving Mirid and of Rhopalimorpha cited above. *
The following categories will be found to exhibit surprisingly little overlapping. The habitats described are, as far as can be ascertained, those in which the species in question spend the greater part of their lives. Seasonal changes in population due to differences between hibernation shelter and summer haunts are indicated in the detailed notes accompanying the main scheme.
(1.) Species confined to Buildings and their Vicinity.—Here belong Cimex lectularius (Cimicidae) and Lyctocoris campestris (Anthocoridae), both, be it noted, practically cosmopolitan, and both more or less parasitic. The apterous Ploiariine, Ploiaria huttoni, occurs in sheds. This is a carnivorous species.
(2.) Widely-ranging Carnivorous Species.—The two Pentatomids Cermatulus nasalis and Oechalia consocialis may be included here. The other predaceous bugs, such as the Reduviidae and Gerridae, are all specialized to a certain extent in habitat.
(3.) Species occurring on Trees, Shrubs, and Lianes.—When the vast extent of originally forested country in New Zealand is considered, it is no matter for surprise to find that more than half the Heteroptera must be included here. A good case could be made out for treating this section as forest species, and bringing in also the forms confined to the leaf-mould which is so characteristic a feature of the forest-floor. Thus would be obtained an unbroken sequence from the upper layers of forest foliage to the leaf-mould stratum itself, the latter being ecologically much more similar to the cortical and subcortical habitat than to any of the terrestrial stations of open country. Such treatment is, however, rendered impracticable—firstly, by the occurrence of numerous phytophagous species on woody plants entirely outside the forest (e.g., Miridae attached to Leptospermum and Cassinia); and, secondly, as mentioned above, by the restriction of various other phytophagous species to botanical families rather
[Footnote] * Evidence will be adduced in a forthcoming paper on New Zealand auchenorrdynchous Homoptera showing, apparently, that these insects are restricted almost as much to plant associations as to botanical families.
than to plant associations. The essentially tropical character of the New Zealand rain forest has here its important effects. The Heteroptera of the forest change their quarters very little throughout the year, and then usually only from one part to the other of the same tree or its vicinity; the trees, with two or three exceptions, are all evergreen, and offer as much shelter in winter as in summer. This is in striking contrast to palaearctic conditions, under which Reuter found a large and varied assemblage of bugs seeking winter quarters on the conifers, which are there practically the only evergreen trees.
The species affecting woody plants and leaves fall readily into the following three minor groups :—
(a.) Those living among live foliage and twigs. Here is included considerably more than half the Miridae; the Lygaeids Targarema stali, Arocatus rusticus, Nysius clavicornis, and Nysius sp. 1; and the Pentatomids Oncacontias vittatus and Zangis amyoti.
(b.) Species occurring among masses of dead vegetation and epiphytes such as mosses and lichens. These are pre-eminently sylvan species. The dense masses of dead fronds (Plate 81, fig. 1) hanging from the heads of such tree-ferns as Cyathea medullaris, and the thick growth of Hymenophyllaceae, Polypodiaceae, mosses, and lichens covering the trunks of trees and logs, afford shelter to the insects of this category. Typical families are Anthocoridae and Reduviidae (Ploiariinae only).
(c.) Species living beneath bark of living or dead trees. The bark of such trees as Dacrydium cupressinum and Podocarpus dacrydioides flakes off, while that of Leptospermum, Fuchsia excorticata, Podocarpus totara, Dracophyllum Traversii is shed in long, fibrous strips, of which several layers may be detached at once. In these situations a considerable number of bugs may be found; but the typical bark-dwelling species, the Aradidae, occur more plentifully beneath the loosened bark of dead trees, thus incidentally proving that the sap of live trees cannot be their main food. Some species of the Aradidae, as mentioned later, occur, particularly in their nymphal stadia, in the forest-floor. The abundance of Aradidae in New Zealand has been already emphasized. The other bark-dwelling Heteroptera include one undescribed Henicocephalid, found with its immature stages in the same situation; an undescribed Ploiariine Reduviid; and a few Anthocorids, the flattened form of which cannot be an adaption to subcortical existence, since it is equally developed in species common elsewhere. Outside Heteroptera may occasionally seek subcortical shelter for hibernation.
(4.) Species occurring on or near the Ground.—These species are more considerably augmented than those of any other section by a distinct winter population of hibernating forms, especially in open country, Four minor groups may be distinguished,—
(a.) Those of low herbage generally (open country). Most of the Nabidae and the Lygaeids, Nysius huttoni, Nysius 'spp. 2 and 3, and Taphropeltus putoni must be placed here. Probably our only Neidid should also be included.
(b.) Species frequenting grasses, sedges, and rushes (Plate 81, fig. 2) (of forest or open country, or both).—A very large number of species is attached to these plants. Among them are most of the remaining Miridae; the only recorded Tingid; the Lygaeids Cymodema n. sp., Orthoea nigriceps, and Margareta dominica; and the Pentatomids Dictyotus caenosus and Rhopalimorpha obscura.
(c.) Burrowing forms. These occur in open country only, and include the Cydnids Hahnia australis and Chaerocydnus nigrosignatus, both more or less attached to the sea-coast. The other Cydnid, Pangaeus scotti, * almost certainly will be placed here when its biology is known.
(d.) Species inhabiting the leaf-mould of the forest-floor. From a strictly ecological point of view these should follow immediately on the groups 3 (b) and 3 (c), to which they are closely related. The majority of them, both in species and in individuals, are Aradids and Lygaeids, especially nymphal instars. The chief species of the latter family belong to the genus Metagerra. Plentiful also, in certain localities, is a species of Henicocephalus, both as nymph and adult. The latter is also, of course, at times a thoroughly aerial insect, its habit of dancing in the air in companies being well known. The leaf-mould is swarming with mites and with the immature stages of numerous other Arthropods, on both of which Henicocephalus possibly preys. Finally, in this habitat occurs the Peloridiid Xenophyes, both as adult and nymph. In passing, it may be noted that several Homoptera spend their earlier stages in the leaf-mould, and one at least (a new genus of Ulopidae) passes there its whole life-cycle.
(5.) Water-frequenting Species.—The anomalies of the New Zealand water-insect fauna have already been mentioned in the introduction. Only five families of aquatic and semi-aquatic Heteroptera occur, and these achieve only the barest representation. They may be grouped in two minor categories :—
(a.) Semi-aquatic forms. The Acanthiidae are numerous in certain localities in individuals, but the number of species is apparently small. While occasionally they venture on to the surface film itself, their chief haunts are the rocks and mud of the shore. The margins of rocky torrents, of rivers, ponds, and lagoons, of the clear lakes, and of the sea itself, yield specimens of these insects.
(b.) Aquatic forms. Here belong the two Corixids and the two Notonectids, both families living most of their time below the surface; and the two Veliids (Microvelia spp.), and the Gerrid Halobates sericeus, all three insects of the surface film, the latter species living on the face of the ocean itself.
The relations of Heteroptera to plants from a floristic point of view have been dealt with under European conditions by Butler (1923) and Reuter (1909). The New Zealand data, though necessarily much more scanty than that collected by the above writers, afford some interesting comparisons. Thus the Orchidaceae, altogether avoided by the British Heteroptera, are similarly shunned in New Zealand, in spite of the fact that the species of indigenous orchids are almost twice as numerous as in Britain. Butler (1923, p. 10) gives a list of other plant-families which are entirely avoided in Britain. Among these the Linaceae and Apocynaceae both contain plants attractive to Heteroptera in this country, Linum sp. yielding Nysius huttoni, and Parsonsia heterophylla (Apocyn.) acting apparently as sole food-plant to Arocatus rusticus. Butler finds the Ranunculaceae, Cruciferae, and Caryophyllaceae with few adherents; in New Zealand these three families are entirely neglected. The Leguminosae are fairly popular, although less so than in England; but the very widespread and abundant introduced Ulex and Sarothamnus, which are among “the special favourites” in their native land, have so far yielded no Heteroptera in New Zealand.
[Footnote] * I am entirely unacquainted with this species.
Yet the similarly introduced Medicago and Trifolium support a considerable number. The Rosaceae, with the Malaceae, are attractive in both countries; but again there is a curious anomaly, in that Crataegus, “the chief favourite” in England, seems here to have no Heteroptera attached to it, although it has been planted extensively in every part of the country. The Umbelliferae are much less frequented in New Zealand than in Britain. The Onagraceae show no cases of definite food-plants in this country.
The Composites are the second most favoured family in New Zealand, and are popular also in Britain. Butler remarks that “the Rubiacaee are particularly associated with certain Capsids, “a fact specially interesting in view of the abundance of these bugs in New Zealand on several indigenous plants of the Rubiaceous genus Coprosma. The Scrophulariaceae are little attractive in either country. Veronica, the chief New Zealand genus, is noted for its astringent properties. The Ulmaceae (introduced in New Zealand) and the Urticaceae yield relatively fewer species than in England, Elatostema in the latter family being singularly barren of insects generally. The Fagaceae are very popular among the Heteroptera of both faunas. The Gramineae support by far the largest number of species in New Zealand, and are strongly favoured in England also. The Juncaceae, very attractive in both countries, are especially used as hibernating-quarters in New Zealand.
Perhaps the greatest contrast occurs in the case of the Pinaceae. In Europe these “are very productive … not only are they the food-plants of many species, but also, as evergreens, they often furnish a winter residence to such species as survive that season in the adult form, since they afford much better protection from the weather than the then leafless deciduous trees. Reuter (19) has recorded 190 species of palaearctic Heteroptera as having occurred on coniferous trees … These he classifies into three groups according as (i) they depend upon deciduous trees or low plants for their food and resort to the conifers only for hibernation, or (ii) are found on both conifers and deciduous trees or low plants even in summer-time, or (iii) occur exclusively on coniferous trees.” In New Zealand the Coniferae are represented chiefly by Taxaceae, which are plentiful and widespread, but from which I can find only four records of Heteroptera, two of which were probably cases of hibernation, while from the two indigenous Pinaceae (Agathis and Libocedrus), and from the numerous and extensively planted imported pines, none of these insects have been taken. As most of the indigenous broad-leaved trees are non-deciduous, the conifers are not necessary as hibernating shelters, while as food-plants the evidence seems to indicate that the Taxaceae in New Zealand are very much less attractive than the Pinaceae in Europe.
The ferns, as might be expected by their abundance in New Zealand, are considerably more favoured than in England, although as food-plants probably not proportionately so. As shelter they attract a number of carnivorous forms.
Among popular New Zealand plant-families which have no representatives in Britain may be mentioned Myrtaceae, Pittosporaceae, Cunoniaceae, Epacridaceae, and Myoporaceae.
The most noteworthy cases of definitely restricted association include those of a Mirid with Pteridium and Cyathea, of Megaloceroea and Rhopalimorpha with Glumiflorae, of Stenotus binotatus with Gramineae, of Margareta dominica with Gahnia, of Romna sp. with Leptospermum, of Arocatus rusticus with Parsonsia, of certain Mirids with Myoporum and with certain Coprosmas
respectively, of Nysius sp. 1 with Cassinia leptophylla, of Nysius sp. 2 with Raoulia tenuicaulis, and of a Mirid with Senecio elaeagnifolius.
To sum up, the most attractive orders in New Zealand, arranged in descending order, are the Glumiflorae, Rosales, Campanulatae and Myrtiflorae (equal), Filicales, Rubiales, Fagales, Polygonales, Liliiflorae. The most favoured families are Gramineae (many introduced plants), Compositae, Juncaceae (especially for hibernation) and Myrtaceae (equal), Rubiaceae, Fagaceae, Polygonaceae, Cyperaceae, Cyatheaceae, Rosaceae, Malaceae (introduced), Leguminosae (chiefly introduced plants), Onagraceae.
Among large New Zealand plant-families from which no Heteroptera have been recorded may be mentioned the following (arranged in descending order, and compiled from Cockayne, 1921, pp. 309—10): Orchidaceae, Ranunculaceae, Borraginaceae, Cruciferae, Gentianaceae, Halorrhagaceae, Caryophyllaceae, Thymelaeaceae, Campanulaceae, Chenopodiaceae. The largest genus of vascular plants in the flora—namely, Veronica—yields only a single record of Heteroptera.
In concluding this section a comparison may be made with Hawaiian conditions, which are more similar than those of Britain. Kirkaldy (1909B, p. 23) writes : “The principal Hawaiian plants, from a hemipterological point of view, are Nani (= Metrosideros) polymorpha, Pipturus, Myrsine, Ipomaea, Sida, various tree-terns, Myoporum; and to a less degree, Acacia, koa, Cyathodes, Elaeocarpus, Eugenia, Freycinetia, Dodonaea, and Bobea. Of these, I find on reference to Kirk's great work on New Zealand forest-trees (the only such work I have for reference) that Cyathodes, Elaeocarpus, Eugenia, Dodonaea, Nani, Myoporum, and Myrsine—and, I suppose, Freycinetia, Ipomaea, and Sida also—are well represented in New Zealand. It is almost impossible to believe that they too are not the shelters or food plants of a large hemipterous fauna there.” Acting on this prophecy, the writer in collecting has always paid particular attention to such of these plants as he has met. Only Myoporum and the tree-ferns have proved specially attractive in New Zealand, at least so far as Heteroptera are concerned. Of the other genera, there are scanty records of Heteroptera from only Cyathodes and Freycinetia.