Manuka Blight Scale Insects Associated with Manuka Species in New Zealand

New Zealand Journal of Agriculture, Volume 89, Issue 6, 15 December 1954, Page 601

Manuka Blight Scale Insects Associated with Manuka Species in New Zealand

By

J. M. HOY,

Department of Scientific and Industrial Research Entomological Research

Station, Palmerston North

AN apparently introduced scale insect of the genus Eriococcus has been artificially established throughout both islands of New Zealand within the past 10 years. The insect is associated with both red manuka (Leptospermum scoparium) and white manuka or kanuka (L. ericoides). Infested plants show a heavy coating of black fungus on the lower leaves and stems. This combination of fungus and insect, known colloquially as manuka blight, is associated with the death of red manuka but not of white manuka. The writer concludes that the insect causing "manuka blight" is now so well distributed that if further artificial transfer were stopped, it is probable that the insect would continue its natural spread into all sizeable areas of manuka. The insect's effect on red manuka affords the most spectacular example of biological control of a plant yet seen in this country.

w Ull LI y o THE majority of the coccids (scale A insects) associated with manuka (Leptospermum) species in New Zealand were described by W. Maskell (1887) in the period 1882-84; the

\X<_>CJ I 7 XIX vllv jJCXXUVI XUO&J U j-j vXXv> locality records were limited and apparently none of the species was considered to be of economic importance. Little work on the coccids of

Distribution of Coccids

manuka was done between that time and 1945. Extensive surveys of the coccid complex associated with manuka were carried out by Sewell (1949) and Hoy (1949). These surveys have been continued up to date. It is now possible to present a clearer

picture of the distribution of the known coccids and to summarise the current information on two apparently introduced species of the genus Eriococcus. >

on Manuka The scale insects recorded by Maskell may be listed in order of frequency of occurrence as follows: Coelostomidia wairoensis Mask., Ctenochiton flavus Mask., Inglisia leptospermi Mask., Lepidosaphes leptospermi Mask.,

aglisia ornatus Mask., and Asterolecanium epacridis Mask. The known distribution of these insects is shown on the accompanying map (Fig. 1). These coccids are relatively confined in distribution- and apparently innocuous to the host plant. It will be seen from Fig. 1, however, that one notable exception to this comparatively restricted distribution is C. wairoensis, a relatively large orangered coccid which is commonly found on white manuka and to a less extent on red manuka throughout the North. Island and the northern portion of the South Island as far south as Peel Forest. The association of this insect with the host is characterised by the presence of large amounts of a black fungus. Infested plants are rarely killed even when this insect is present in large numbers. The two species of Eriococcus fall into a different category in that they are both definitely harmful to the host plant. A disease of red manuka characterise:! by the appearance of a heavy

The darkened areas are those where the species is . established. Dots indicate infestations which are not yet extensive.

growth of sooty mould on the infected plants was noted in the upper Orari Gorge about 1937. By 1945 a considerable portion of the manuka in the Geraldine district had been killed. Investigation showed the presence of an eriococcid (referred to in this article as Eriococcus sp.). A survey by Sewell (1949) showed distribution of this new species in Canterbury from Fairlie in the south along the foothills to the Okuku Range near Amberley. The majority of isolated manuka stands on the Canterbury Plains were also infested. No insects were reported from the North Island. Hoy (1949), however, recorded the presence of this species at Tangoio (near Napier), and Wairoa. These areas had been artificially infested with insects from the Geraldine district between 1945 and 1946. Today Eriococcus sp. has been transported artificially to many other localities and

is established widely throughout the North and South Islands, the range being from south of Lake Manapouri to Kaitaia. In Canterbury Eriococcus sp. has become established, largely by natural spread, over 4| million acres. In the Wairoa area,'partly by natural spread from the introduced infestations at Tangoio and Waihi (Wairoa County) and partly by artificial distribution, the area of infestation has grown from approximately 60 acres in 1945 to 1| million acres today. In North Auckland there are now two large areas infested, one in the Kaitaia-Kaikohe region of approximately 850,000 acres and another near Warkworth of 25,000 acres. On the west coast there is

an area of 100,000 acres near Raglan and another of 10,000 acres at Kawhia. These figures do not imply that the whole of these areas is occupied by manuka, but within these districts it is difficult to find a stand of any size which is not carrying the insect. Taken together these areas represent approximately 11 per cent, of the land area of the main islands. Other areas from which Eriococcus sp. has been recorded are shown in Fig. 2. In the areas indicated by a dot on the map the infestation is not yet extensive, though in some places the rate of spread is increasing rapidly. The only large tract of manuka in the North Island from which the insect has not been recorded lies between Lake Taupo and the coast at Opotiki. The distribution shown on the map is by no means complete, but it does show that the insect is capable of establishing under a wide range of climate. A second species of Eriococcus (leptospermi Mask.) was recorded by Hoy (1953). Its distribution is still relatively confined in the area between Hanmer, the mouth of the Conway River, and Kaikoura (Fig. 1). This species was described by Maskell (1890) from red manuka and Leptospermum laevigatum in Australia. Its occurrence in an isolated locality in New Zealand is difficult to explain. E. leptospermi is apparently capable of killing red manuka in New Zealand. Unfortunately the locality in which it occurs has been overrun by the other eriococcid species (Eriococcus sp.), which makes the study of E. leptospermi as a separate entity rather difficult. Appearance and Habits of Eriococcus sp. and E. leptospermi Plants of both red and white manuka infested with Eriococcus sp. show a heavy coating of a black fungus on the lower leaves and stems. This fungus, which was identified as Capnodium walteri Sacc. by Mulcock (1954), does not penetrate the. plant tissue and is dependent on the continued production of honey dew by the insect. Scattered on the surface

of this “mould” are small white flecks, the cocoons of the male puparia. When the outer covering of fungus and loose bark is removed, the females and immature stages of the insect can be seen. . ... , ... . The female is sheltered within a greyish white sac; once fixed to the plant by its rostrum the female remains m one position. The female is about l/25m. long and is discernible to the naked eye. The male is the only winged stage, small and inconspicuous apart from its two ample iridescent wings and a pair of long waxen caudal filaments. The nymphal stage or “crawler” is somewhat like the female in appearance, but is smaller and moves about. _ The female and crawler of E. leptospermi resemble those of Eriococcus sp., but the two insects may be separated on .the host plant, as the sac of the female of E. leptospermi is always exposed, whereas that of

Eriococcus sp. is hidden beneath the exfoliated bark. - Eriococcus sp. has one generation per year under Canterbury conditions, crawlers being found free on the plant in maximum numbers during the 6 weeks from mid-April. Dispersion of the insect occurs during the nymp h a 1 period. Under natural conditions the most active spread is by wind-borne crawlers. Spread is therefore more rapid with the prevailing wind than against it. Numerous examples of the effect of wind on the rate of spread may be seen in the Wairoa area. . The establishment of this insect appears to be little affected by either altitude or climate. Scattered manuka plants in the high valleys of the Southern Alps are heavily infested, as are small heath-like plants growing on exposed ridges at altitudes of approximately 3000 ft. In the North Island plants have been infested at altitudes higher than 2500 ft. Where the degree of exposure is severe the rate of build-up of the insect is slowed down and plants survive longer from initial infection. Place of Origin The origin of Eriococcus sp. remains obscure. The insect is not known to entomological institutions overseas and though Australian authorities place it close to E. leptospermi, it differs from that species in a sufficient number of characters to warrant specific status. E. leptospermi appears to be an introduction which can be traced back to its original habitat, but it is difficult to explain its occurrence in an isolated

area such as the Conway River valley, Similarly Eriococcus sp. was first noted in an isolated area, the upper Orari Gorge. It is possible that these ' insects were accidentally introduced on ornamental varieties of manuka, but such explanation would not account for their presence in the redded r “ S in which they were first leeoiueu. Effect of Eriococcus on Host A stand of red manuka infested with Eriococcus sp. may be distinguished by the blackened pearance of the lower portions of the plants, only the canopy foliage retaining its normal green. Plants. carrying high populations of the insect sometimes show accelerated tip growth for a short time before death. The first symptom of approaching death of the plant is the Thi s wn n?fmallv occur s C “t P a time of changing ecological conditions Sh as thF lowering of the soil Stu?! /evil or the onset of frosts e on e iy h thTskeleto? of°the Sant 3 e to““ years XT'betweTn initiS thTcKlapse nZfhl tSanY d collapse or tne pia t. When heavily infested plants are sprayed with insecticide and the insect is eliminated the plants recover and continue to grow normally.. This indicates that no plant virus is . involved. Death of the plant may be due to direct insect feeding, to the production of toxins, to reduction in photosynthetic activity due to the presence of sooty mould, or to any combination of these factors. Expertmental work along these lines is now proceeding. This much is certain; the

insect is primarily responsible for death of the plant, since the fungus (associated with Eriococcus in manuka blight) is dependent on the continuing production of honey dew by the insect for its existence, The relative Immunity rol white The relative immunity of white manuka is difficult to explain. This plant is readily attacked by Eriococcus sp . and though t he population density of the insect reaches high levels, very few plants are killed. This Eriococcus sp. has not been recoV ered from any plants other than red and w hit e manuka, but other plants growing close to infested manu k a are sometimes coated with black fungus growing on honey dew dropped from the infested plant, 11 Spread and Control Sprays Within the space of 10 years Eriococcus sp. has been artificially established throughout both islands. It is now so well distributed that if SUed It Is probable that the insect Si "Snug I *A dis? of New z aland , s indigenous flora is outside the scope of this article. One fact is clear: The effect of this nsec t on red manuka affords fh e mos f spectacular example of biological control of a plant yet seen in this country, The insect may be controlled with oil emulsions or a spray consisting of either 50 per cent, para para isomer wettable D.D.T. or 10 per cent, gamma B.H.C. nicotine sulphate, and a wetting agent in the proportions 8 : 1: 8 in 800 parts of water. Such sprays, though

useful for specimen plants or small stands, would be neither feasible nor economic on a national scale. Lack of knowledge of the Eriococcus species overseas suggests that in its original habitat it has been kept in check by natural enemies. A search could be made for these parasites or predators, but this may easily be long and expensive. References J. M. Hoy, “Control of Manuka by Blight”, “The New Zealand Journal of Agriculture”, vol. 79, pp. 321-324, 1949. “First Record of Occurrence of Eriococcus leptospermi Mask, in New Zealand”, “New Zealand Entomologist”, vol. 1,- No. 3, p. 1, 1953. W. M. Maskell, “The Scale Insects (Coccidae)”, 1887. “Further Coccid Notes”, “Transactions and Proceedings of the New Zealand Institute”, vol. 23, pp. 22-23, 1890. A. P. Mulcock, “A Disease of Manuka Leptospermum scoparium Forst.” “Transactions of the Royal Society of New Zealand”, vol. 82, No. 1, pp. 115-118, 1954. T. G. Sewell, “Manuka Blight Survey”, “The New Zealand Journal of . Agriculture”, vol. 79, pp. 101-104, 1949.

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• Coelostomidia wairoensis 1 Eriococcus leptospermi 2 Inglisia leptospermi 3 Inglisia ornatus 4 Lepidosaphes leptospermi 5 Ctenochiton flavus 6 Asterolecanium epacridis