The New Zealand Species of Oliarus (Hem. Cixiidae)
Entomological Research Station, Department of Scientific and Industrial Research.
[Read before the Nelson Institute, October 20, 1952; received by the Editor, November 3, 1952.]
Characters which distinguish the two species O. oppositus and O. atkinsoni are described.
Myers (1924) redescribed Oliarus oppositus (Walk.) and described an additional species Oliarus atkinsoni. Recently, adults of the latter species have been shown to transmit the “yellow-leaf” disease of Phormium tenax Forst. (Cumber, 1952). O oppositus, although breeding on a wide variety of plants, is often found in the adult stage feeding on the blades of Phormium, but as yet has not been incriminated as a vector of the disease, whereas O. atkinsoni is largely restricted to Phormium as a host plant. The purpose of the present account is to indicate the characters (some of which were not described by Myers) which readily separate the two species.
Characters Distinguishing the Two Species
a. O. oppositus is usually yellow-brown in colour, whereas O. atkinsoni is grey.
b. The macrotrichia are more conspicuous in O. oppositus.
c. O. oppositus is much the smaller species although considerable variation in size occurs in both species-e.g., O. oppositus 4.6–7.0 mm., O. atkinsoni 7.2-9.4 mm. (vertex to extremity of tegmen, wings folded).
d. In O. oppositus the vertex is relatively broader than in O. atkinsoni (Fig. 1). A series of specimens of both species collected at different localities gave the following ratios for maximum width of frons. width of vertex at level of posterior carina. (Measurements were made with a micrometer eye-piece 1 mm. = 178 units.)
|Mangamuka||17. 2.51||2. 02, 1.84||2.00|
|New Plymouth||29.11.48||1.86, 2.22||1.99, 1.99, 1.86, 2.04|
|Ngauranga||1. 2.51||1 86, 2.10||1.93, 1.97, 1.89, 1.84|
|Paraka (Shannon)||4. 1.50||1.96, 2.16, 2 05||1.82, 2.01, 1.76|
|Puketi Forest (Kaeo)||11. 2.51||2.00|
|Mangamuka||17. 2.51||2.61, 2.71||2.71|
|Omapere (Okaihau)||5. 3.50||2.70, 2.48, 2.55, 2.86, 2.63, 2.79|
|Paiaka||24.11.49||2.85s, 2.96, 3.00||2.61, 2.55, 2.63|
It is seen that these ratios do not overlap in the two species.
e. In O. oppositus the frontal carina is continued as a lighter-coloured raised area for only a short distance into the clypeus, whereas in O. atkinsoni it continues to the tip of the latter (Fig. 1).
Fig. 1.—The head of O. oppositus (L.) and O. atkinsoni, showing the relatively broader vertex in the former, the extension of the frontal carina in the latter, and the shape of the fronto-clypeal sutures.
f. The fronto-clypeal suture of O. oppositus takes the form of a wide-based inverted “U,” whereas in O. atkinsoni the suture is more acute and is “V”-shaped (Fig. 1).
In both species as a preliminary to copulation, the individuals will line up alongside and level with each other, and it is not uncommon to see as many as five bugs (central female with two males on each side) placed in this manner. Where adults of both species are present at Paiaka on the Phormium, it has been noted that the males of one species will often take up position alongside females of the other species.
Cumber, R. A., 1952. The Experimental Induction of the “Yellow-Leaf” Condition in Phormium tenax Forst. by the Insect Vector Oliarus atkinsoni Myers (Hem. Cixiidae) N.Z. J. Sci. Tech. In press.
Myers, J. G., 1924. The New Zealand Plant-hoppers of the Family Cixiidae (Homoptera). Trans. N.Z Inst., Vol. 55, pp. 315-326,