THE NATURAL ENEMIES OF THE CHAFF SCALE, PERGANDII COMSTOCK, IN ISRAEL (*)

BY

Uri C-ERSON

The chaff scale, COI~ISTOCK [Homoptera: Coccoic[ea: ] is a pest of mature citrus groves along the coastal plain of Israel. Though usually considered to be a minor pest (EBELING, 1959) the chaff scale has also been known to cause economic damage (~[ERRILL, 1953; DEAN, 1955 a.o.). Research carried out in Israel on this scale and some of its natural enemies was summarized by HARPAZ (1961), while ROSEN (1965) added data concerning its parasites. GERSON (1964) found that the populations of the chaff scale in Israel are intermingled with those of the tropical grey chaf scale, Parlatoria cinerea HADDEN.

Sampling and reporting procedure The sampling methods of the chaff seale population and its natural enemies are described in detail elsewhere (GERsON, in prepa- ration). It may be sufficient to note here that all samples were obtained from mature citrus trees, aged 25-30 years or more. The samples were collected from all above-ground parts of the trees, namely leaves, fruit and bark of trunk and limbs. On fruit, the various areas, i.e., calyx, sides and style, were examined and recorded separately. The activity of the natural enemies is reported in two ways. The presence of parasites or specific predators may be expressed as per unit of the host (or prey) population. Non-specific, free living predators, however, are not found in conjunction with their prey, hence their presenee was merely estimated. This was done by counting all live predator specimens seen during regular examinations of samples of 400 live Parlatoria females. This wilt be discussed later.

(*) This research has been financed in part by Grant No. FG-Is-227 made by the United States Department of Agriculture under P.L. 480.

ESTOMOP}IAGA,X~ (Z), I967, 97-IO9 98 u. GERSON

Predators Chilocorus bipustulatus (L.) [Col. Coccinellidae]. This polyphagus predator is an important enemy of citrus scale in Israel (AvlDOV, 1961). Its habit of congregating on the trunk and main limbs of citrus trees (RosEN & GERSON, 1965) is probably related to the great abundance of live Parlatoria on these parts throughout the year. The phenology of C. bipustulatus was recently studied by ROSEN & GEI~SON (1965). They found that the populations of this predator reached their peak in midsummer, declined during autumn and winter. They also pointed out (loe. eit.) that this predator may play a more important role in limiting scale-insect populations than at that time realized. The fact that C. bipustulatus appears to be the main vector of the predaceous mite, Hemisareoptes coeeophagus MEYER (GEaSON, 1964) lends much support to the above suggestion regarding the economic importance of Chiloeorus.

Lestodiplosis sp. [Dipt. Ceeidomyiidae]. All members of this large genus are predaceous during their larval stage. They feed mainly on members of their own family (BAa~'ES, 1928), but have also been reported to attack scale insects (BARNES, 1930). The reddish, long-necked larva of Lestodiplosis usually' lies under the cover of the scale, its mouth-parts touching the body of the scale. Otherwise, the larva is curled up, there. Pupation takes place at the site of feeding. Monthly observations at many groves did not reveal any definite seasonal trends in the abundance of this predator; however, it appears to be slightly more numerous in spring and autumn. The exact determination of this species is rather difficult (W. NIJVELDT, personal communications, 1963-1965), and there is some indication that more than one species or genus is involved.

Hemisarcoptes coccophagus MEYEIt [Acar. Astigmata : Hemisar- coptidae]. This predaceous mite is a specific enemy of armoured scale insects, disseminated, during its hypopal stage, by Chilocorus bipustulatus. During the present investigation it was found that H. coccophagus is abundant in the summer months, both as a scale-insect predator and as a Chilocorus-borne hypopus. Like all other chaff-scale pre- dators, it attcks its prey mainly on the trunk and main limbs of the trees. A fuller discussion of this species is presented elsewhere (GEasoN, 1967). NATURAL ENEI~IIES OF Parlatoria pergandii 99

Cheletogenes ornatus (CANESTRINI ~% FANZAGO) [Acar. Prostigmata : Cheyletidae]. C. ornatus, a well-known enemy of scale-insect crawlers (McGaE- aoa, 1956; GEaSON, 196~), is not an active predator, but rather prefers to ambush its prey. It is usually found under empty scales. Chele- togenes seizes the passing crawler by its powerful palpi and sucks it up dry. Year-round samplings show (Fig. 1), that this predator appears in greatest numbers during the summer months. It may at times be the most abundant mite species on citrus bark, but is seldom found on the leaves or fruit.

Cheletomimus berlesei 0UDEMANS [Acar. Prostigmata : Cheyle- tidae]. According to EBELING (1959), this speeies is an important predator of the latania scale, Hemiberlesia lataniae (SIGN). On eitrus it was found to be less abundant than C. ornatus, though it may be the dominant aearine predator of scale insects in selected groves.

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2 --T-T-- ~ 4- ~o o Chetetomimus ber~eaei ~. -- 5aniosulus nudu5

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III V VII rX XI I Ill FIG. 1, Seasonal abundance of Cheletogenes ornatus on citrus bark (a = Mash'mia Shalom; b = Kefar Warburg), "expressed in terms of 5 distinct categories (0 = no mites; 1 = up to 5 mites; 2 = up to 20 mites; 3 = up to 80 mites; 4 ~ more than 80 mites). FIG. 2, Seasonal abundance of Cheletomimus berlesei and Saniosulus nudus on citrus bark, at Rosh I-IaNiqra, expressed in terms of categories as in Fig. 1. 100 U. GERSON The seasonal trend of a C. berlesei population is presented in Fig. 2. Like the other chaff-scale predators herein discussed, i~ is most abundant during summer, on the bark of the trees.

Saniosulus nudus SUMMEaS [Acar. Prostigmata : Eupalopseltidae]. S. nudus is an active, quick moving predator of chaff-scale crawlers. The prey is held by the anterior legs of the mite as it inserts the che- lieerae into the crawler's body. Feeding may proceed for about 30-40 minutes, until the prey is sucked dry. It is then pushed off the ehelicerae with the mite's long palpi. The mite was not seen to feed successfully on an adult Parlatoria because it seemed unable to pene- trate cuticle of the female. The predator is less abundant, on eitrus than the aforementioned cheyletid mites. The population trends of S. nudus are also presented in Fig. 2, whence it can be seen that this predator is most numerous on citrus during summer. S. nudus was also found to be feeding o-~ the crawlers of various other Diaspidids in this country. S. nudus was first described by SUMMERS (1960) from 2 females obtained in Mexico and Texas. Apparently no other mention of this species occurs in the literature. DEAN (1955), however, discusses a very close association between cha//scale and a mite (undeseribed genus, ]amily Stigmaeidae)... observed/eeding on first stage scale and scale eggs on citrus in Texas. The present writer examined a specimen of this Stigmaeid, kindly forwarded by Dr. Herbert A. DEAN, of Weslaco, Texas, and found it to be Saniosulus nudus SUMM~ItS.

Eupalopsis maseriensis (CANESTRINI • FANZAGO) [Acar. Prostig- mata : Eupalopsellidae]. This uncommon predator was mainly found in one isolated citrus grove. Its feeding habits are similar to those of Saniosulus.

Parasites Aphytis hispanicus (MERcET). Prospaltella inquirenda SILVESTRI [Hymenoptera : Aphelinidae]. These two species are the dominant parasites of the chaff scale on citrus in Israel. They were first recorded in this country by RosEN (1965), who also mentioned two other, less abundant Aphytis spp. as attacking P. pergandii. The population trends of A. hi.spanicus and P. inauirenda were studied from samples collected at various observation plots along the coastal plain. All scMes were exarrAned ~.nd dissected in the laboratory under a stereoscopic microscope and the percentage of live and parasitized scales determined. From these vzlues the rate NATURAL ENEMIES OF Parlatoria pergandii 101 of active parasitism was calculated, i.e. the percentage of live scales containing living parasites from the total of parasitized and unparasi- tized (live) scales of a given instar. Initially, the sample from each plot consisted of 1,000 scales. Later, as it was found that both parasites attack mainly the Parlatoria females (Table 1), samples of 400 living females were counted. All Figures (3-10) pertain to active parasitism in Parlatoria females only.

PARASITE POPULATION TRENDS ON CITRUS LEAVES AND BARK. Table 1 and Fig. 3-6 show the active parasitism rates and trends of the parasites when they attack leaf-infesting scales, whereas Fig. 7-8 pertain to parasitization of scales on the bark.

3 4

3G I I E I i I I I I I I ~h~ ] Prospaltella Wo

25

20

10

I III V VII IX XI II IV Vl VIU X XII FIo. 3-4, Rate of active parasitism by Aphytis and ProspalteUa in chaff scale populations on citrus leaves. -- 3, Y[adera; 4, Kefar Warburg. Table 1 Percentages of active parasitism in population samplings of 1,000 chaff scales on citrus leaves (Hadera).

SECOND LARVA FE,~IALE MALE PUPA ~[ONTII Live scales Active parasitism in % Live scales Active parasitism in % Live scales Active parasitism in % in % Aphytis Prospaltella Total in % Aphytis Praspaltella Total in % Aphytis Prospaltella Total

JANUARY ...... 13.7 ------23.3 '13.7 9A 23.1 7.0 7------FEnaUARY ...... '15.5 ------30.6 7.5 t~.2 t'I.T 7.6 ------MARClt .... : .'... tt,.2 ------30.6 t~.9 4.2 9.t t~.0 -- 2.5 2.5 APart ...... i7.7 -- l.l t.1 29.8 3.7 5.7 9A 6.5 6.2 -- 6.2 MAY ...... 17.3 4.6 -- ~',.6 t5.2 'I6A 12.5 28.9 10.9 3.7 3.7 7.4

JUNE ...... 3.6 ------t0.0 It,.0 3.0 '17.0 t.0 ------

JULY ...... 8.6 ------it.5 2.6 0.9 3.5 2.5 ------AUGUST ...... 6.1 ------7.9 2.5 t.3 3.8 2.9 3A 3A 6.8

SEI'TEMREa ..... It*.2 ------i8A 2.8 5.0 7.8 3.5 ------

OCTOIIER ...... t5.5 ------t8A 1.6 6.0 7.6 4.5 ------

NOVE~tRER ..... "15.8 ------'18.3 9.8 3.3 13.1 ~.3 ~.7 -- 4,7 DECE~tRER ..... 16.3 '1.2 1.2 2A 17.8 6.7 5.'1 tl.8 9A '1.1 -- t.1 NATURAL ENEMIES OF Parlatoria pergandii 103 Because no parasitism was observed in first-stage larvae, these are absent from Table 1. Second-stage larvae and male pupae rarely supported live parasites. Autumn and spring were the seasons of the highest activity of both parasites. There was a distinct decline taking plade in the summer months. However, in their relative (to each other) abundance, these species differed in the various plots sampled. Thus, in the grove represented by Fig. 3, both occurred in about equal numbers. In the groves shown in Figures 4 and 5, 94 ~ and 75 ~ respectively of all parasites attacking the chaff scale were P. inquirenda. At the Cartoon orchard (Fig. 6) A. hispanicus was dominant, providing 80 ~ parasitism. Thus it is concluded that the two parasites occur in more or less equal numbers on citrus leaves. On the bark, however, 84 ~ and 99 ~ respectively of all parasites at the Rosh Ha Niqra and Kefar- Warburg groves (Fig. 7 and 8) were P. inquirenda. At the various plots, ~both parasites destroyed about I1-20 ~o of chaff scale females on the leaves throughout the year. On bark this value came only to 7-8 ~ probably as a result of the reduced activity of A. hispanicus thereon. Laboratory observations showed no evidence of host feeding or mutilation by the two Aphelinids. The development of parasite progeny on or in li~ve scales must therefore be considered as the only parasite-induced mortality cause.

PARASITE POPULATION TRENDS ON CITRUS FRUIT. As indicated in Fig. 9 and 10, P. inquirenda was the dominant parasite on fruit. This finding as well as those pertaining to parasitism on the bark (Fig. 7 and 8) suggest that the other parasitic species, A. hispanicus, is unable to fill all microhabitats occupied by the chaff scale. No differences in parasite activity were found on the various parts of the fruit (calyx, surface, style), although the eMyx usually supports more than 70 ~ of the Parlatoria population throughout the growing season (GERSON, in preparation). This is probably because the calyx itself protects the scales below from parasite activity. The population trends of the parasites on the fruit differed from those on the other tree parts. The initial (July-August) parasitism was relatively high, and later it declined (Fig. 9). On sour lemon fruit, however, a secondary peak occurred in the winter (Fig. 10). This deviation from the observed seasonal trends on other citrus varieties is apparently due to differences in scale exposure, as discussed below. During the early period of fruit development, a gap remains between the fruit and its calyx. Infestation of citrus fruit by Parla- toria begins during June (GE~SON, in preparation) and is followed 104 u. GERSON by parasite activity. This is the initial summer peak shown in Fig. 9 and 10. Later in the season the gap closes, so that the parasites cannot reach the protected scales. This situation prevails till the end of the growing season with most citrus varieties. In late autumn the sour lemon fruit shed some of the calyx ~ sepals ,, the scales are exposed and there is a rise in the activity of the parasites (Fig. 10). It may be seen on the fruit, that parasitism is partly dependent on the stage of fruit development, because this, in turn, determines the degree of scale exposure.

SOME OBSERVATIONS ON HOST-PARASITE RELATIONSHIPS. Aphytis hispanicus and Prospaltella inquirenda were also found to attack the tropical grey chaff scale (Parlatoria cinerea HADDEN) in considerable numbers. Observations at groves, where P. cinerea dominated, showed that parasitism trends were similar to those presented-above (Fig. 3-10). No evidence could be obtained that either one or both parasites preferred one or another of the host scales. Both parasites were also collected from the olive scale, Parlatoria oleae (CoLv~E), obtained from apple trees, Hafez-Hayyim, December 6, 1964. One single female of P. inquirenda emerged from a second-instar female of the California red scale, Aonidiella aurantii (MASK.), obtained on citrus leaf, Kefar-Warburg, December 1964. Under laboratory conditions, A. hispanicus was continually bred on the latania scale, Hemiberlesia lataniae (SIGN.). Rearing experiments revealed the presence of a race of P. inquirenda, which developed in the Florida red scale, Chrysomphalus aonidum (L.), the ivy scale, Aspidiotus hederae (~TALL.) and H. lataniae. Members of this race did not develop in Parlatoria spp. DEAN (1965) has recorded Prospaltella ]asciata ?r aS a negligible parasite of the chaff scale in Texas. Through the courtesy of Dr. Herbert A. DEAN of Weslaco, Texas, the present author has received several specimens of the Texas Prospaltella. They were reared in Rehovot on chaff scale and subsequently examined. As no morphological differences could be found between them and the local material, it is concluded that the Texas Prospaltella is in reality P. inquirenda. Separation between these two species of Prospaltella was made according to the key and descriptions presented by FERRI~RE (1965).

Azotus sp. Several specimens of an Azotus sp. were occasionally reared, during the spring months, from samples of Parlatoria spp. infesting citrus in the central coastal plain of Israel. 25

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7

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III V Vll IX Xl III 10 I I I I i I I LII,II Olo

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VII IX XI i III

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4

II IV Vl VIII X X!I II IV VI VIII X

Fro. 5-10, Rate of aetive parasitism by Aphytis and Prospaltella in ehaff seale populations. -- 5, eitrus leaves, Rosh HaNiqra; 6, leaves, Carmon; 7, bark, Rosh I-IaNiqra; 8, bark, Kefar Warburg; 9, citrus fruit, Hadera; 10, eitrus fruit, Carmon. 106 u. GERSON" Azotus is usually considered to be hyperparasitie, attacking parasites of armoured scale insects or whiterflies (FEuad~aE, 1965). This is the first record of the genus from Israel.

Discussion

Ten species of parasitic or predatory insects and mites were found to feed on various stages of the chaff scale during the present investigation, and 2 other parasites recorded by RosE~" (1965). The dominant parasites, namely A. hispanicus and P. inquirenda, showed marked differences in their activity in respect to the various citrus-tree parts. While they appeared in approximately equal numbers on citrus leaves, Prospaltella was found to be dominant on the bark and fruit. This is clearly seen by comparing Fig. 6 to 10, which represents data collected on leaves and fruit on the same dates in the same grove. FLANDERS (1956) has suggested that natural enemies of scales search the surface of leaves and fruit more effectively than the surface of the trunk and branches. This difference in search- ing ability might explain the dominance of Prospaltella on bark. This parasite's numerical superiority on the fruit, however, indicates that additional, unknown factors are involved. DOUTT and DEBAc~t (1964) consider that the ability of the natural enemy to occupy and survive in MI the host-inhabited niches is an important attribute of the effective natural enemy. The present data demonstrate that A. hispanicus does not have this attribute. This might well result in the reduced parasite activity on the bark of the trunk and main limbs of the trees (Fig. 7-8). It is of interest to note that in Texas, 3 species of Aphytis are the dominant chaff scale parasites, while Prospaltella is of negligible importance (DEAN, 1965). - Both Aphytis and Prospaltella were found to parasitize the chaff scale mainly during spring and autumn. The various predators, on the other hand, are more numerous in the summer. This is parti- cularly significant, as summer is considered to be the critical period in the build-up of armoured scale-insect populations on citrus in Israel (BoDENHEIMER, 1951). Chaff scale populations infesting older, mature gwoves in this country, though subject to seasonal fluctuations, still show a marked stability in their numbers (BODENHEIMER, 1951, 1958; GEaSO.~', in preparation). Such stability suggests that these populations have achieved a degree of balance within their environments (HuFFAKER & MESSENCEa, 1964). From the present study, and a corollary one concerning the phenology and biology of the chaff scale (GERso.<, in preparation) it is now possible to review the various components of NATURAL ENEMIES OF Parlatoria pergandii 107 the environment of this pest throughout the year, and try to evaluate the relative importance of its natural enemies. Autumn is a period of stepped-up parasite action. The pre- vailing lower temperatures slow down the development of the scale. Crawlers are blown off the trees by the winds and storms, which also tear off infested fruit, leaves and branches. All these scales are obviously lost to the population. During winter the low temperatures and storms intensify their effect. Though natural enemy activity is low, large chaff scale- populations are removed from the orchards in the course of fruit picking. In the spring, the parasites are very active, and the predators begin to build up their populations. Furthermore, the Khamsin (*) winds, which begin in late spr~ng, are most detrimental to scale insect survival (BODENHEIMER, 1951). Summer is the season of most intensive predator action. The aforementioned Khamsin winds blow in early and ]ate summer. It is also the season during which certain agroteehnieal treatments, such as whitewashing, pruning and spraying are applied with an adverse affect on the scales. Other summer effects noted (GERSOX, in pre- paration) are reduced female fecundity and high mortality of scales on insufficiently irrigated citrus trees. The various factors which inhibit the numerical increase of chaff scale are particularly effective against the leaf populations. Those on fruit are transitory, whereas the bark populations appear to be somewhat tess affected by climatic conditions, but somewhat more by natural enemies (especially predators). The over-all picture is that throughout the year both density- dependent and density-independent environmental factors are present, to limit the populations of P. pergandii. At the critical, summer period, the various factors appear to act in an complementary manner. During this season the chaff scale population ebbs (GERSON, in pre- paration), possibly because of the combined effect of parasite activity in the spring, the reduced scale female fecundity, and especially the Khamsin winds. The surviving scales will build up next year's populations, hence any mortality factor which will further reduce the number of survivors, will consequently help to lower it. As mentioned above, the main mortality factors during summer (possibly excepting pesticide treatments) are the natural enemies, with special reference to predators. It thus becomes evident that during the critical summer decline, intensity of natural enemy action might well determine the level of next season's infestation.

(*) An extreme weather condition well-known in the Middle-East, characterized by hot and dry desert winds. Temperatures may rise 1o over 40 ~ in the shade, and relative humidity drops to below 30 per cent, sometimes to 5 per cent. 108 U. GERSON In this context, it is pertinent to quote CHANT (196~) : Neither density-dependent or climatic ]actors are always responsible ]or the regulation o/ populations ; which is responsible and the details o/ its action vary in time and place and with the animal at hand... One must view the pest not as an isolated phenomenon but as a product o/ its environment including all major elements, both biotic and abiotic. Furthermore, the present writer agrees with LAWSON (1938) that The ecological hypothesis that insects are controlled by the whole ecosystem seems to be a much more realistic concept than the earlier ideas. It is postulated that in the case of the chaff scale infesting mature citrus groves in Israel, the populations of this pest are control]ed not by any single environmental factor, but by their whole ecosystem.

ACKNOXVLEDGMENTS The author wishes to express his sincerest gTatitude to Prof. Z. AvlDOV,-under whose guidance this study was eolldueted in p~rtial fulfillment of the requirements for the degree of Doctor Of Philosophy, for his many helpful suggestions. Thanks are also due to Prof. I. HARPAZ for criticM reading of the manuscript; to Dr. D. ROSEN for determination of Hymenopterous parasites; to Dr. W. NIJVELDT, of Wageningen, for identification of Lestodiplosis ; to Drs. Magdalen~ K. P. MEYER, of Pretoria, and F. M. SUMMERS, of Davis, for help in determining various Acarina, and to Dr. H. A. DEAN of Weslaco, for sending specimens of natural enemies from Texas.

RESUMI~ Dix esp~ces d'Insectes ct d'Acariens sont signaMs comme pr~dateurs et parasites des stades divers de Parlatoria pergandii COMSWOCK [Homoptera : Coccoi- den : Diaspididae] sur agrumes en Israel. Les pr~dateurs sont : Chilocorus bipustu- latus (L.) [Coleoptera: Coccinellidae], Lestodiplosis sp. [D~ptera: Cecidomyiidae] et cinq esp~ces d'Acariens. Ces pr~dateurs ont ~t~ observes pendant t'~t~ sur le trone et les branches principales des arbres. Les insectes parasites sont : Aphytis hispanicus (MERCET), Prospaltella inquirenda SILv. et Azotus sp., ce dernier ~tant un hyperparasite rare. Les deux premiers se sont r~v~l~s abondants h l'automne et au printemps et un peu plus rares en ~t~. Leur taux de parasitisme est sensi- blement ~gal lorsqu'ils s'attaquent h P. pergandii sur feuilles d'agrumes tandis que P. inquirenda domine lorsque l'h6te est localis6 sur les fruits et l'~corce des arbres. Le stade de d~veloppement du fruit d~termine le degr~ d'exposition de Pi pergandii l'action des entomophages. On suppose que les populations de P. pergandii sont r~gularis~es par Faction combin~e de facteurs divers, d~pendants et ind~pendants de la densitY. BIBLIOGRAPHY Awnov, Z. -- '196t. Pests o[ the Cultivated Plants o[ Israel. -- The Magt~ess Press, The Hebre~v University, Jerusalem, 5/*6 pp. (In Hebrew). B.&RNV.S, If. F. -- '1928. British gall midges. 2. Lestodiplosis KIEVVEa. -- Entomol. mon. Mag., 64, 68-75, t42-V~8. --1930. Gall midges [Cecidomyidae] as enemies o~ the Tingidae, Psyllidae, Aleyrodidae and Coccidae. -- Bull. ent. Res., 21, 319-329. NATURAL ENEMIES OF Parlatoria pergandii 109 BODENIIEINEII, F. S. -- t95'1. Citrus Entomology in the Middle East. -- IV. Junk, The Ifague, 6i;3 pp. -- 1958. Aniinal Ecology To-Day. -- W. ,h~td,', The Hague, 276 pp. CnA~T, D. A. -- 3.964. Strategy and tactics of insect conirld. -- Canad. Ent., 9fi, 3.82- 201. DEa.w, H. A. -- 1955. Factors affecting biological control o~ scale insecgs on Texas citrus. -- J. econ. Ent., 48, 444-447. -- 1965. An Aphytis complex [Hymenoptera : Eulophidae] of chaff scale. -- Ann. ent. Soc. Amer., 58, 142-t45. DOUTT, R. L. & D,~B,tclt, P.- 1964. Some biological control concepts and questions. -- In: DEBAcH, P. (edit.). Biological Control of Insect Pests and Weeds, p. 119-3.42, Chapman and Hall LTD., London. EBELfNG, W. -- 1959. Subtropical Fruit Pests. -- Univ. Call[. Div. Agric. Sci. Publ., 436 pp. FERRII~.I/E, Oh. -- 3.965. Les Aphelinidae d'Europe et du Bassin m6diterran6en. -- Faune de l'Europe et du Bassin m6diterran6en, vol. I, Masson ddit., Paris, 204 pp. Fza.~DEns, S. E. -- 3.956. Struggle for existence betweett red and yellow scale. -- Cali[. Citrogr., 41, 396-403. GERSON, U. -- '1964. Parlatoria cinerea, a pest of citrus ia [srael. -- FAO Pl. Prof. Bull., 12, 82-85. -- t967. Observations on Hemisarcoptes coccophagus ~[EYER [Astigmata: Ilemisarcoplidae] with a new synonym. -- Acarologia, in press. GEnSON, U. -- Studies of the chaff scale, Parhttoria pergandii, on citrus in Israel. -- In preparation. HARPAZ, [. -- 3.961. Coccoidea. In : Z. AwDov, Pests of the cultivated Plants or' Israel, p. t26-3.75. The Magnes Press, Jerusalem (Hebrew). HUFFAKEI1, C. B. & MESSENGER P. S. -- t964. The concept aud signillcance of natural control. In: P. I)EB,tcn (edit.) : Biological Control t~l' Insect Pests and Weeds, pp. 74-t3.7. Chapman and Hall LTD., London. L,twsoN, F. H. -- ]958. Some features of the relation of insects to their ecosystems. -- Ecology, 39, 53.5-523.. MCGREGOR, E.A. -- 1956. The mites tff citrus trees in southern California. -- So. Call]. Acad. Sci. l~lem., 3 (3), 1-42. ~[EIIRILL, G-. B. -- 1953. A revision of the scale-insects o[ Florida. -- State Plant Board o[ Florida, Bull. No. 1, 143 pp. P~OSEN, D. -- ]965. The hymenopterous parasites of citrus armored scales in Israel [Hymenoptera : Chalcidoidea]. -- Ann. ent. Soc. Amer., 58, 388-396. PtOSEN, D. t% CtERSON U. -- 1965. Field studies of Chilocorus bipustulatus (L.) on citrus in Israel. -- Ann. Epiphyties, 16, 73.-76. SuMMm~s, F. M. -- 3.960. Ettpalopsis and Eupatopsellid mites [Acarina: Stigmaeidae, EttpalopseUidaeJ.- Flo. Entomol., 43, 3.19-3.38.

(The Hebrew UnivErsity, Faculty o/ Agriculture, Rehovot, Israel.)