The Life History of Lecanium (Eulecanium) persicae (Fabricius), and Descriptions of the Different Instars.
[Read before the Canterbury Branch, March 29, 1939; received by the Editor, April 26, 1939; issued separately, March, 1940.]
There are found in New Zealand some Coccidae belonging to the subfamily Coccinae which, in their natural state, and also when examined microscopically, are very similar in appearance. These apparent species, or varieties—whichever one may prefer to call them—have for many years puzzled students of this group, so much so, in fact, that at the present time no one appears willing to identify them positively, but all prefer to place them in what is usually called the “persicae” group. There are quite good reasons for this procedure, seeing that the original description of L. persicae dates back as far as 1762 or 1766. According to Newstead (1902), the author of the name was Geoffroy, in 1762, but Marchal (1908), on the other hand, gives the credit to Fabricius in 1766, in which he is followed by Green (1930). Seeing that there is a doubt about the name of the author, it is little wonder that there has long been a doubt about the identity of the species, and that the list of synonyms is somewhat longer than usual, and that no two lists should be the same.
Still further to complicate the matter, Douglas (1885) confused L. persicae with at least two quite distinct species, i.e., L. corni Bouche and L. coryli Linn. This mis-identification by Douglas was later carried on by Newstead and Green in various publications on the British Coccidae. Marchal (1908) was the first to give a good definition of the species, and pointed out the mistake of Douglas, and his finding was later confirmed by Green (1930), who gave a diagram showing the important distinctions between L. corni Bouche and L. coryli (Linn.), showing clearly that they should by no means be confused with L. persicae (Fab.) when examined miscroscopically. Green also stated that the latter species was not indigenous to the British Isles, nor had it up to then been recorded as an introduced pest in greenhouses.
From time to time I have collected exotic species of Coccinae, but till within the last two years had never made any systematic study of them. Towards the end of 1937 there were found on the common broom plant in Motueka numerous specimens that did not agree with others under the same name in my collection, which had been identified by Mr. Green. As the literature available on this subject was limited, it was thought best to send out specimens to other students, which was accordingly done, specimens being sent to both U.S.A. and Italy. Up to the present time, the only replies received have come from the Entomological Department at Washington, U.S.A., where Mr Harold Morrison has identified specimens as belonging to the “persicae” group. Owing to the confusion that at present exists
in this group, he did not care to go further in the matter and make a more definite statement. In the meantime, I had gone on studying the species, collecting specimens from a large number of plants, preparing and examining them in all the stages that could be procured. Green (1929) had already reported the species as occurring on grape vines from Whangarei, and specimens were collected on grape vines from two different places in Motueka. These, on examination, appeared to show two different varieties, neither of which agreed with specimens collected on Wistaria at Ngatea, in the North Island. This appeared to be undoubted evidence of more than one variety of the species in this country, and it became difficult to know which of them was likely to be the species indicated by Fabricius. Green (1929) had simply mentioned the fact that the species was present in New Zealand, and in 1930 had merely stated that both he and Newstead were mistaken in the identification of L. persicae in England. It was not until Marchal's concise work on the subject became available later on that it was possible to identify what I now believe to be typical specimens of L. persicae. Though Marchal evidently made a very close study of this species, he makes no mention of any variation. This may be accounted for by the fact that he did not always make a close microscopic examination of the specimens collected, but sometimes relied on their appearance in the natural state. As the insects under these conditions vary only slightly in colour, he may have overlooked differences.
Given the fact that Marchal's description of L. persicae was correct, there was little doubt that some of those collected on grape vines were typical specimens (and the same may be said of certain specimens collected from plum, honeysuckle, and gooseberry), but that other specimens collected from broom, Pittosporum, Wistaria, and other plants of grape-vine and plum in Motueka were a variation from the typical species. The specimens collected on Wistaria at Ngatea were distinct again from either of the others above mentioned. The fact became evident after the examination of a large number of specimens taken from different kinds of plants, that they could not possibly be what is called “host variations,” and the matter became still more complicated later on when young insects were examined as they became available, for not the slightest difference could be distinguished between them. There is no doubt about the species being exotic and, as rather a long list of synonyms is attached to the specific name, there will always remain a probability of any variety having been already described under one or other of the many names attached to the species in the past. The possibility, however, of any such proof being given is very remote. In the early days of their study, the description of these insects was almost wholly confined to their appearance in the natural state, when colour, size, shape, habitat, together with a very short description of the antennae, was thought to be quite sufficient. The usual method of preparation in those days was that of clearing in oil, and as staining was out of the question, many of the finer characters—such as minute pores and spines— would be practically invisible. This makes it extremely doubtful that even if the original specimens were examined, their identity with those
now living could be confirmed. Under these circumstances, and in the light of our present knowledge of the species, it has been thought best to attach a name to any variation from the typical that gives every indication of being permanent.
Marchal undoubtedly made a very close study of several species that have been placed in this subgenus, and gives a very good description of all the supposed instars, with the exception of the larval instar of L. corni Bouche. From observations made during the last fifteen months, there is little doubt that Marchal's second instar of L. corni is really that of L. persicae, while his second instar of L. persicae should have been the third instar of that species. After all, it is not surprising that such a mistake should have occurred, when we consider that both species are very prevalent in Europe, and are often found together on the same plants, for under such circumstances it would be very hard to distinguish between the intermediate instars of the different species. One of the most important differences between the two species when in the adult instar is the presence of submarginal tubercules in L. persicae, and their entire absence in L. corni. The real function of the submarginal tubercules is as yet obscure, but from each there is exuded a long waxy thread that is more apparent in the young insects than in the adults. Whether or not these tubercles are present in the intermediate instars of L. corni I cannot affirm, owing to these instars not being available in my collection, but judging from what is known of other species, there seems to be no reason why they should be. One fact that many enlighten us as to the identity of typical persicae is that Marchal (1908, p. 290), in referring to the submarginal tubercules, states as follows: “Elles sont de chaque côté au nombre de 5 à 6 avant la première échancrure stigmatique; 2 entre les 2 échancrures stigmatiques; 7 (parfois 6) entre l'échancrure stigmatique postérieure et la fonte anale soit donc une trentaine sur toute la périphérie. Leur nombre d'ailleurs est variable, mais dans des limites d'une très faible étendue; on peut parfois trouver 14 glandes d'un côté et 15 glandes de l'autre sur le měme individu.”
There is little doubt that this information as to the submarginal tubercules is important when taken in conjunction with an eight-jointed antenna. With 14 to 15 tubercules on each side, this would mean from 28 to 30 tubercules for the insect; moreover—and this will be very important to remember when we refer to the descriptions of the different variations found in New Zealand—there are two tubercules on each side between the anterior and posterior stigmatic areas. Judging from this, one would be apt to believe that if certain specimens are found in New Zealand with a seven-jointed antenna, with not more than half the number of tubercules—and with only a single tubercule between the two stigmatic areas—they certainly do not agree with the description of L. persicae given by Marchal, and, unless good proof to the contrary is given, should be placed as a distinct species.
Marchal is very positive as to the eight-jointed antenna of L. persicae, for he states as follows: “Antenne (fig. 34). Assez longue, grěle, de 8 articles (et non de 7 comme chez L. corni).” This
is clear proof that he had not then found any specimen with a seven-jointed antenna. He also makes no mention of the stout conical spines in L. persicae, and this is an oversight that is hard to understand seeing that he draws attention to the very minute ones found on the derm of L. corni.
Regarding the size of the insects, one must allow for a great, deal of variation in the adults. The greatest variation that has yet come to my knowledge is from 4 mm. to 9 mm. in old adults taken from the same plum tree. This is well worth bearing in mind, for in the past the question of size alone has apparently been used in the separation of the species. Both colour and shape are just as useless as size, and the only safe guides are the various pores, glands, and spines found on both the dorsal and ventral surfaces of the body. The antennae are, to a certain extent, useful, but too much reliance should not be placed on them unless supported by other characters. The legs are quite useless, but the plates of the anal complex must be considered as one of the best and most consistent guides to classification owing to the fact that they vary so little during the whole life of the insect, from the second instar to the adult.
In spite of the long time that this species has been known to science, its life history has not, up till now, been fully worked out, as discovered from observations made during the last fifteen months. By some mischance, Marchal appears to have mistaken the second instar, which is not surprising when we consider the size of the insects and the difficulty one has in finding the larvae once they have spread. The growth of the insects during the first three instars is very slow, and it is not until after the third moult in the spring that much change in size takes place. Before the first moult the submarginal tubercules are absent, their place being taken by a double row of ten 8-shaped pores on the dorsum, which extends submedially from the anal complex to the thoracic segment. A side view of these pores shows them as very small twin projections of the derm.
The larvae first make their appearance about the middle of December, and immediately spread over the plant, usually making their way to the tender young shoots, or, in the case of the grapevine, beneath the loose bark of the older limbs. Having fixed their location, they insert the rostral setae and remain fixed until the first moult occurs about the middle of February. Characters worth noting in the larvae are the 8-shaped pores and the very short, subequal, stigmatic spines.
The first moult having taken place, the 8-shaped pores are found to have disappeared, the plates of the anal complex have lost the very long stout seta, the middle stigmatic spine has become much longer, and what are known as the submarginal tubercules have made their appearance, there being four pairs. The anal cleft has become much more prominent, and now extends well below the anal plates. The antenna, however, still remains six-jointed as in the larva, but the tarsus is now slightly shorter than the tibia.
About the middle of April, the second moult takes place, and there has now been added another joint to the antenna, making it seven-jointed, there has been a slight increase in the length of the tibia, although actually the legs remain about the same size, and the number of submarginal tubercules is doubled. Apart from these slight changes, there is no appreciable alteration except a very slight increase in size.
One lucky enough to prepare specimens just before the moult takes place can observe several facts worthy of notice. The new skin —together with the marginal setae and stigmatic spines—is seen to be fully formed before such parts as the legs, antennae, anal complex, and submarginal tubercules. All these latter are seen to be still in a soft state, which is still further exemplified by the way they take the stain. Another fact is that the rostrum is cast off entire, together with the rostral setae, and the new setae can be seen neatly coiled upon each side of the new rostrum. It may also be observed that the submarginal tubercules are developed in quite a different place from, where they are in the previous instar.
For the next seven months very little alteration takes place, even in size, until about the second week in October, when the first adults make their appearance, and it is easy to recognise those that have just moulted by the presence of a little white pellet above the anal complex. The stigmatic spines are now very much longer, and are again subequal; the submarginal tubercules have again nearly doubled in number; in typical specimens another joint has been added to the antenna, and six transverse bands of large multilocular pores have made their appearance on the ventral surface between the anal complex and the posterior pair of legs, with a group of similar pores near to the coxae of the anterior and middle pairs of legs. For some reason, probably climatic, the antenna and the submarginal tubercules may remain as in the pre-adult instar, but in such instances the multilocular pores are always present, and as stated before, these pores can always be looked on as signs of sexual maturity. After the last moult, the insects increase rapidly in size, and when egg-laying begins, become more and more convex, while at the same time the derm assumes a darker hue, and becomes quite hard, with a slight longitudinal carina. About the end of November, egg-laying commences, and at the end of December the first of the young larvae will have made their appearance. The times given here are approximate only, as it has been noticed that the time of moulting, egg-laying, or hatching of the eggs may extend over a period of at least a month, but in this district, at least, there is only one generation a year.
A description of the various instars and varieties of L. persicae found in this country follows:—
Lecanium (Eulecanium) persicae (Fabricius).
Coccus persicae Fab., Gens. Ins. Mani., 1766, p. 304.
Lecanium persicae (Fab.), Marchal, Soc. Ent. de France, vol. 77, 1908, p. 285.
Larva. Emerges end of December. Antenna of six joints, last joint slightly longer than the third, formula: 6, 3, 5 (1, 2, 4). Rostrum and mentum normal. Legs normal, rather stout, tibia and
tarsus about equal. Spiracles normal, placed close to the margin, with which they are connected by a row of three small quinquelocular pores; stigmatic spines in triplicate, very short, subequal. Plates of anal complex roughly triangular, appearing in mounted specimens to be divergent, and not extending beyond the posterior margin of the body; with one very long seta at apex and another very short on each side of it. The usual three pairs of stout setae on the ventral surface above the anal complex. Marginal setae present, simple, longest and stoutest at either extremity. Submarginal tubercules net recognised. Tubular ducts not observed. On the dorsum there are two submedian longitudinal rows of what look like 8-shaped pores; these are very small, and each row extends from the anal complex to just above the rostrum, when the insect has been flattened on the slide. A side view of these pores shows them like very small twin projections of the derm. There are ten in each row. Length of insect, 0.34 mm.; width, 0.18 mm.
Larva moult middle of February.
Female of Second Instar. Elongate, not chitinised, flat. Antenna of six joints, third joint longest, formula: 3, 6, 2 (1, 5) 4. Rostrum and mentum normal. Spiracles normal, connected with the margin by a single row of quinquelocular pores; stigmatic spines in triplicate, the middle one being much the longest and thickest. Legs normal, very stout. tibia slightly longer than tarsus; one digitule of claw thicker than the other. Anal cleft moderately deep, open. Eight submarginal tubercules, two on each side behind the posterior spiracles, one on each side between the anterior and posterior spiracles, and a pair above the anterior spiracles near the antennae Plates of anal complex roughly triangular, set close together; inner margin longest, straight, base shortest and slightly concave, outer margin convex, apex rounded, with three small setae at apex and another in an indentation on the inner margin. There are about four fairly long and stout setae at the margin of the vellum, and three pairs of long stout anal-ring setae. The usual three pairs of stout setae on the ventral surface above anal complex, and, on a level with the middle pair, there is a transverse row of five minute spines. A sparse submarginal band of small tubular ducts round body. Marginal setae present, simple. Length about 1.04 mm.; width about 0.37 mm.
Second moult middle of April.
Female of Third Instar. Elongate, flat, soft, not chitinised. Antenna of seven joints, third joint longest, formula: 3, 4, 7, 2, 1 (5, 6). Rostrum and mentum normal. Spiracles normal, connected with the margin by an irregular row of quinquelocular pores; stigmatic spines in triplicate the centre one being much the longest and thickest. Legs normal, stout, tibia one-third longer than tarsus; one digitule of claw thicker than the other. Anal cleft open. Plates of anal complex roughly triangular: inner margin longest, straight, with a single indentation towards apex; base shortest, straight or slightly concave outer margin convex, apex rounded; with one fine seta near outer margin and about three more at apex. With from fifteen to seventeen
submarginal tubercules on the dorsal surface arranged as follows: three to five on each side behind posterior stigmatic area; one between anterior and posterior stigmatic areas; four to seven in half circle above anterior stigmatic areas. Marginal setae present, similar to those of the previous instar. The usual three pairs of setae above the anal complex, and on a level with the middle pair there are five very minute spines in a transverse row, the two outer ones being in pairs, with a wider interval separating each pair from the centre one. Length about 1.10 to 1.48 mm.; width about 0.60 mm. to 0.82 mm.
Third moult about 15th October.
Early Adult Female. Ovate, flat or slightly convex, soft, with a somewhat wavy outline. Antenna of eight joints, third joint longest; formula: 3, 4, 5, 2, 8, 1 (6, 7). Rostrum normal. Spiracles normal, with a broad band of quinquelocular pores connecting with the margin; stigmatic spines in triplicate, long, subequal in length, the centre one being slightly thicker than the others. Legs normal, slender, tibia two-thirds longer than tarsus. Marginal setae differing in length and thickness, about three on each side of anal cleft being very thick; with an inner row of very short fine setae. Anal cleft not fused, but with the margins sometimes overlapping. Plates of anal complex roughly triangular: in typical specimens the inner margin is longest with two indentations, in each of which there is a stout seta; base shortest, straight or slightly concave; outer margin convex, and apex rounded with three short setae. In abnormal specimens in which the antenna is seven-jointed and with about sixteen sub-marginal tubercules, the anal plates are similar to those of the previous instar. Ventral surface with the usual three pairs of stout setae above anal complex. A broad band of multilocular pores surrounds the anal complex, with six transverse bands above, the uppermost being between the hind pair of legs; a loose scattered group of pores near to the coxae of the anterior and middle pair of legs. A broad submarginal band of tubular ducts is on the ventral surface. Two longitudinal rows of stout spines, submedian, on the ventral surface, and a few more scattered indiscriminately. Dorsally, a submarginal row of large tubercules is arranged as follows: seven to nine on each side behind the posterior stigmatic area: two—sometimes three—between the anterior and posterior stigmatic areas; nine to eleven in a half circle above anterior stigmatic areas. Two very stout and three fine setae near inner base of each antenna. Length of early adults 2.34 mm. to 4.40 mm.; width about 1.87 mm. to 2.88 mm.
Old Adult Female (Typical). With dorsal derm deeply chitinised, hard, convex, with a distinct longitudinal median carina. Antenna of eight joints, third joint longest, formula: 3, 4, 5, 2, 8, 1 (6, 7). Spiracles normal, connected with the margin by a broad band of quinquelocular pores. Stigmatic spines in triplicate, long, sub-equal. Legs normal, slender, tibia much longer than tarsus. Anal complex normal. A broad submarginal band of tubular ducts on ventral surface, also derm spines and large multilocular pores, but full particulars not obtainable owing to dense chitin of the dorsum.
Dorsum with numerous small clear areas of cells, giving the derm a punctate appearance; these are most numerous towards the margin of the body and sparse in the centre; the cells surrounding the anal complex and along the margin of the cleft are oblong and larger. Submarginal tubercules present on dorsum as in early adult. Length 4.65 mm. to 9.20 mm.; width about 3.50 mm to 6.28 mm.
A variation sometimes found is where the adult female remains as in the third instar, the derm becomes convex and deeply chitinised, the same punctate appearance is to be seen as occurs in typical specimens, and the large multilocular pores are also present, showing that the insects are sexually mature. Such females do not appear to reach the large size found in typical specimens.
Hab.: On grape, broom, honeysuckle, plum, gooseberry, hawthorn, tree lucerne, lemon, Pittosporum sp., Aristotelia sp., Wistaria sp., Motueka, N.Z.
Lecanium (Eulecanium) persicae (Fab.) spinosum n.subsp.
Early adult female. Elongate-ovate, with a wavy outline, lightly chitinised, fairly soft, slightly convex. Antenna of eight joints, third or fourth joints longest, formulas: 4, 3 (2, 5) 1, 8, 6, 7 or 3, 4, 8, 2 (1, 5) 6, 7. Rostrum and mentum normal. Legs normal, slender, tibia one-third longer than tarsus; one digitule of claw thicker than the other. Spiracles normal, connected with the margin by a broad band of quinquelocular pores; stigmatic spines in triplicate, the centre one being slightly longer and thicker than the others. Anal cleft open. Plates of anal complex roughly triangular; inner margin longest, with three indentations, in each of which there is a fairly stout seta; base shortest, straight; outer margin convex, apex rounded with three short setae. Multilocular pores present on ventral derm, very numerous, there being a broad band surrounding the anal complex, and seven transverse bands above, the uppermost being between the middle pair of legs. A submarginal band of tubular duets on ventral surface, those at the cephalic extremity being fever and more scattered. Ventral derm spines present, very large and conical, with blunt points, those at the posterior extremity in irregular transverse rows. Marginal setae present, simple, also the usual three pairs above anal complex. Very large submarginal tubercules present on dorsal surface, numbering from twenty-eight to thirty, arranged as follows: seven to nine on each side behind posterior stigmatic areas; two between anterior and posterior areas; ten in half circle above anterior stigmatic areas. In old adults he dorsal derm is hard and chitinised, convex, and is evenly punctured with small clear areas or cells. Length of early adults about 2.34 mm.; width about 1.58 mm. Length of old adults 6.80 mm.; width 5.40 mm.
Hab.: On Wistaria sp., Ngatea, N.Z.
This is undoubtedly a distinct variety, and it differs from typical L. persicae (Fab.) in the following particulars: in having an extra notch and seta on the inner margin of the anal plates, in the much larger submarginal tubercules, in an additional transverse band of
large multilocular pores, in the much larger and differently-shaped ventral spines, and in the dorsal derm-cells being evenly spread over the dorsum. I consider these variations to be sufficient for the erection of a sub-species, but not for a species.
I would like to thank all those who have in any way helped me in the study of this species. To Mr. Harold Morrison my thanks are due for mounted specimens of L. persicae (Fab.) collected in the United States, to the Entomological staff of the Cawthron Institute for allowing me the use of their library, and to others for collecting material.
Cockerell, T. D. A., 1906. The Coccid genus Eulecanium, Can. Entom., March, 1906, p. 83.
Douglas, 1891. Ent. Mo. Mag., vol. 2, March, p. 65.
Geoffroy, 1764. Hist. ab. des Ins., p. 506.
Green, E. E., 1929. Some Coccidae Collected by Dr. J. G. Myers in New Zealand, Bull. Entom. Res., vol. 19, pt. 4, March, p. 376.
—– 1930. Observations on British Coccidae, Ent. Mo. Mag., vol. 66, p. 12.
Marchal, P., 1908. Notes sur les Cochenilles de I'Europe, Soc. Entom. de France, vol. 77, p. 285.
Newstead, R., 1902. A Monograph of the British Coccidae, Ray. Soc., vol. 2, p. 89.
Signoret, 1873. Essais, pp. 235 and 484.