Eriophyoid Mites - Their Biology, Natural Enemies and Control E.E. Lindquist, M.W. Sabelis and J. Bruin (Editors) �9 1996 Elsevier Science B.V. All rights reserved.

173

Chapter 1.4 Biology and Ecology

1.4.1 Life Forms, Deuterogyny, Diapause and Seasonal Development

D.C.M. MANSON and G.N. OLDFIELD

Only during the past few decades have we begun to gain insight and under- standing into the structure and biology of eriophyoid mites. Increasingly, we are learning that these most minute arthropods display frequently variable and complex life cycles that enable them to be extremely resilient and adapt- able to their environment. They have a tenacity of life that far exceeds their small and often fragile appearance. As we examine their life forms and sea- sonal development we can readily see why this is so.

LIFE FORMS AND DEUTEROGYNY

A simple life cycle

Life forms can best be examined initially by taking a simple life cycle and examining the various stages of such a cycle. The mite commences life as an egg 1), passes through two immature stages and finally emerges as an adult. The immature stages are sometimes referred to as larval or nymphal , or the first instar may be called a larva and the second instar a nymph. In accord with Chapter 1.1.1 (Lindquist, 1996), the terms "larva" and "nymph" are used for the subsequent immature forms so that we have:

EGG --~ LARVA --~ NYMPH ~ ADULT

A quiescent or resting stage occurs between larva and nymph, and between n y m p h and adult. Sternlicht and Goldenberg (1971) call these stages the "nymphochrysalis" and "imagochrysalis" respectively.

Eggs are laid on leaves or amongst buds. They are usually spherical or el- liptical and often difficult to see when first laid as they may be colourless or translucent. The eggs are small, about 20-60 gm in diameter, but quite large when compared to the size of the maternal mite. For instance, the eggs of the apple rust mite, Acu lus schlechtendali (Nalepa), are about 50 gm in diameter, compared with a body length of 170-180 gm for adult females. As observed by Shevchenko (1957) for Eriophyes laevis Nalepa, the larva is folded back on

1) There are a few exceptions: Abou-Awad (1981) describes Metaculus mangiferae (Attiah) where the female produces hatched larvae; de Lillo (1991) also cites 8 other species in which ovoviviparity has been noted.

Chapter 1.4.1. references, p. 182

174 Life forms, deuterogyny, diapause and seasonal development

itself in the egg. Eggs may change shape and colour within a few days of being laid and become more visible. Eggs usually hatch in a few days.

Immatures are usually similar to adults in appearance, but of a smaller size and lack external genitalia. There are other differences: in the number of dor- sal and ventral rings, the dorsal shield markings and direction of the prodor- sal shield setae, and in the number of microtubercles. The nymph of the filbert bud mite, Phytoptus avellanae Nalepa, differs from the usual pattern in that it is distinctly different from the adult, being flat, with broad tergites and laterally projecting fleshy points. The immatures of many species have never been studied, but those that have include Aceria victoriae Ramsay (Ramsay, 1958), Aceria mangiferae Sayed (Abou-Awad, 1981), Aculus schlechtendali (Nalepa) (Easterbrook, 1979), Aculus fockeui (Nalepa and Trouessart) (Put- man, 1939) and Phytoptus avellanae Nalepa (Keifer, in Jeppson et al., 1975).

Adults consist of females and males, but females always seem to be more numerous and for some species males have never been found. Sternlicht and Goldenberg (1971) in their study of the citrus bud mite, Aceria sheldoni (Ewing), state that at a temperature of 24-30~ fertilised females laid eggs that produced offspring consisting of 7-25% males. Males are similar to fe- males, but slightly smaller, without a genital coverflap and with different genitalia (see Chapter 1.1.1 (Lindquist, 1996)).

Deuterogyny

This type of life cycle is more complex than the previous one in that there are usually two forms of adult female, but only one form of male. The first form of female, which structurally corresponds to the male, is the protogyne. The male and female together constitute the perfect or primary form and in a sense correspond to the male and female of the previous life cycle. The other form of female is the deutogyne or secondary form.

The first indication of deuterogyny in an eriophyoid mite was given by Putman (1939) in his account of the plum nursery mite, A. fockeui (= Phyllo- coptes fockeui). He mentioned the occurrence of female overwintering forms or hibernating forms, which occurred when the foliage began to harden in the hottest part of summer. He distinguished the hibernating form or deutogyne by the absence of well-developed ova, which are conspicuous in actively breeding females.

However, it was Keifer (1942) who first gave a clear explanation of deuterogyny, derived from his study of the buckeye rust mite, Tegonotus aes- culifoliae (Keifer) (= Oxypleurites aesculifoliae). This species is common on buckeye in California, U.S.A., and can cause a severe rusting on both leaf sur- faces. Two forms of female were discerned in May and June (see Fig. 1.4.1.1). One is generally flattened, with broad dorsal opisthosomal plates bearing a central ridge and projecting as lateral lobes, typical of many Oxypleurites species. The other form of female is quite different and possesses structural characteristics of the genus Phyllocoptes. The Oxypleurites-type was found to consist of both males and females, whereas the Phyllocoptes-type occurred as the female form only. Oxypleurites is therefore the primary form. These two forms of female are so different that Keifer originally described them as dis- tinct species.

Differences between protogynes and deutogynes Keifer, in Jeppson et al. (1975), presented the main differences between

these two forms. In general there are differences in microtuberculation- deuto- gynes having a reduced or suppressed microtuberculation, or the microtubercles

Manson and Oldfield 175

may have a different shape. This is comparable to the situation in spider mites (Tetranychidae) in which there is a loss of dorsal strial lobes from the integument of some species during diapause (Jeppson et al., 1975). Rust mite deutogynes show even more obvious differences, by having narrower tergites, and any ridges, furrows or protuberances occurring in the protogyne are absent in the deutogyne. The prodorsal shield of deutogynes usually has less orna- mentation. However, there may be some cases where the distinction is slight, and breeding experiments may be necessary to confirm the presence of deuterogyny.

o

" ' - ' ~ , : : . ~ - NIDA ~a#~. r .

"'" '" "I"";"":""

]PLATS lOO---Oxypleuritea aeFculifolla~ K. Il lustrating all s tages I'LATB I 6 7 - - / C p | t r l m e r u s p l r l l ' o l l A e K. deutogyne P

Fig. 1.4.1.1. Different life forms of eriophyoid mites. (a) Tegonotus aesculifoliae (Keifer) (= Oxypleurites aesculifoliae K.) (b) Epitrimerus pyri (Nalepa)(= Epitrimerus pirifoliae K.); from Keifer (1942). Designations on plates: APi=Internal-female genitalia; CD=Cross sec- tion of deutogyne; CP =Cross section of primary form; DA=Dorsal view of anterior shield; ES=Structure of side skin; F=Featherclaw; GFD=External genitalia of deutogyne; GFP=Ex- ternal female genitalia of primary form; GF= Female genitalia and coxae; L1, L2=Front and rear legs; Nl=Side view of larva; NIDA=Anterior dorsal shield of larva; N2DA=Anterior dorsal shield of nymph; NIVA=Anterior ventral view of larva; N2=Side view of nymph; O=Egg; S=Side view of mite; SD=Side view of deutogyne; SP=Side view of primary male.

Purpose of deutogynes Deutogynes promote survival through adverse conditions. The suppression

or modification of microtubercles on the opisthosoma is thought to provide a means for hibernating deutogynes to conserve body fluids by rendering the cuti- cle more resistant to water loss (Krantz and Ehrensing, 1990). Leaf hardening, particularly in the case of leaf vagrants and rust mites, triggers the production of deutogynes in late spring or summer, usually in association with rising sum- mer temperatures. In some instances, particularly with species occurring in er- inea or galls, the vital factor is the onset of cool conditions in the autumn. Deutogynes here appear much later in the year. Deutogynes move off the leaves into sheltered crevices on twigs, under bud scales or around lateral buds; in these protected sites they hibernat and in some cases aestivate. The deutog-

176 Life forms, deuterogyny, diapause and seasonal development

ynes will have been inseminated prior to going into their winter quarters, but it has been shown they cannot produce eggs in the year of their occurrence. They have to go through a period of winter cold, followed by rising spring tempera- tures before they begin breeding (Hall, 1967b; Jeppson et al., 1975). In spring they emerge from hibernation to lay eggs in developing buds, these eggs giving rise to protogynes and males. Fig. 1.4.1.2 shows the life cycle of a typical deuterogynous mite.

S U M M E R

S P R I

N G

99 Primary types

&

Deutogynes 199 Primary types

eggs laid in spring buds

f

Primary types &

Deutogynes

move into crevices and around buds

for aestivation and hibernation

Deutogynes

W I N T E R

Fig. 1.4.1.2. Life cycle of a typical deuterogynous mite.

Primary types -- & A

Deutogynes U

�9 T U M N

move into hibernation sites

leaf fall Primaries die

Occurrence on evergreen hosts Until about 1975, deuterogyny was thought to be confined to eriophyoids on

deciduous plants. Then Keifer (1976) described Eriophyes adenostomae (Kei- fer) from the evergreen plant, Adenostoma fasciculatum in California. This plant has needle-like leaves of about 3-8 mm long. The deutogyne is about the same size as the protogyne, but the microtubercles are distinctly larger and subelliptical. This seems to be the first record from an evergreen host. It is of interest to note that males occurred during the winter.

Manson (1984) recorded deutogynes for two species on the evergreen host Nothofagus menziesii (Fagaceae) in New Zealand. This is thought to be the first record of deuterogyny on evergreen hosts from the southern hemisphere. One of the mites was Aceria simonensis Manson. The deutogyne differed in the suppression of the dorsal microtubercles, the reduced number of tergites and stemites, the presence of a triangular anterior shield lobe and the reduced dor- sal shield markings. Also, some deutogynes seemed to have a weak longitudi-

Manson and Oldfield 177

nal abdomir~al ridge or trough. Aceria waltheri (Keifer) is the other species occurring on N. menziesii which also has a deutogyne. The dorsal microtuber- cles of the deutogyne are greatly suppressed or absent. Aceria waltheri was associated with a leaf erineum, rather than a "witches' broom" from which it was originally described.

O c c u r r e n c e on tropical h o s t s The report by Hassan and Keifer (1978) of a deutogyne for the mango leaf

coat ing er iophyid, Cisaberoptus kenyae Keifer, was the first record of deuterogyny in a tropical species. The species was present in colonies under a white coating on mango leaves. It is widespread in the tropics occurring in southern Asia, east Indian islands, Africa and South America. The deutogyne is unusual in that it has a spatulate or shovel-nosed rostrum, stocky legs and large complicated featherclaws, features not shared by the male or protogyne. The deutogyne is the commonest form seen and seems to be principally con- cerned in tending the white coating and keeping the coating raised enough to provide mite space for the colony members. The deutogynes were shown to be active egg-layers, not having a "delayed oviposition" as is the case with tem- perate region deutogynes.

A second tropical species considered by Keifer (1977) to be deuterogynous is Aceria binarius Keifer. This occurs on Peltophorum pterocarpum (Leguminosae) in Thailand. The mites cause a longitudinal rolling of the leaflets, with thickening developing in the rolls.

Atypical deuterogyny In most cases, the distinction between deutogynes and protogynes is readily

apparent, when there is a realisation that a mite species may have two forms of female. There are however, some instances where a species may be suspected as being deuterogynous, but the differences are so slight and so different from typical forms that it is difficult to be certain. For instance, Keifer (1966) de- scribed Dicrothrix anacardii Keifer and D. secundus Kei fe r - both very similar species morphologically - from the cashew, Anacardium occidentale Lam. There is a possibility that one of these "species" may be a deutogyne of the other species.

Keifer, in Jeppson et al. (1975), also mentioned a possible case of deuterog- yny in the grass mite, Aceria tenuis (Nalepa). Two sizes of female come from the drying seed heads. The larger females had internal eggs or larvae and are regarded as the reproductive form. The smaller females lack internal eggs or larvae and are probably the migratory form that often is dispersed by wind. The smaller form may be considered to be the "deutogyne".

A similar situation is recorded by Somsen (1966) in the case of the wheat curl mite, Aceria tulipae (Keifer). A migratory form is recognised that is prob- ably associated with changes in temperature and /o r the condition and amount of food. This migratory form differs in size and colour and moves more actively on the plant. It is difficult to distinguish and a practiced eye is needed.

Manson (1984) suspected deuterogyny in Aceria titirangiensis Lamb. The apparently deuterogynous form has a long hind claw and a faint "eye spot"; the other form has a hind claw of normal length and a distinct "eye spot". There seems to be no difference in microtuberculation between the two forms. Males possess a distinct "eye spot" and a hind claw of normal length.

Keifer, in Jeppson et al. (1975), mentioned the possibility of non-structural deuterogyny occurring in some species, that is, a deutogyne that is virtually the same as the protogyne, but has a migratory habit, typical of deutogynes. One such species is Aceria erinea (Nalepa), the walnut er ineum mite. Mites

178 Life forms, deuterogyny, diapause and seasonal development

move out of erinea during summer and migrate to terminal buds in a similar manner to the deutogyne of Aceria brachytarsus (Keifer).

Keifer (1969) makes the intriguing observation that some species may have more than two forms of female that are characteristic of typical deuterogyny. Aculops rhoicecis Keifer is regarded as being in this category; a species which seems to have a gradation of forms between the typical protogyne and typical deutogyne.

Eriophyes emarginatae Keifer, the chokecherry finger gall mite, forms leaf pouch galls on leaf upper surfaces of several species of Prunus in Califor- nia. Oldfield (1969) studied this species and found that it was quite remark- able, in that only the secondary form of female, or deutogyne, was present. The protogyne female is absent, though the male is present. This appears to be the only species where only the deutogyne form of female is known.

Trisetacus kirghisorum Shevchenko is a mite that lives on junipers in Sibe- ria, Russia, and is characterised by a two-year life cycle. It is reported to have two forms of male and female, and seems to be the only known species with this type of life history (Shevchenko, 1967).

Krantz and Ehrensing (1990) noted that the deutogynes of Aceria chon- drillae (Canestrini) are highly unusual in that they overwinter in the wet basal stem tissue of Chondrilla juncea. Normally, eriophyoid deutogynes seek dry and well-protected loci for hibernation. The deutogynes of A. chondrillae were dark brown in colour, in contrast to the opaque white or tan of the protog- ynes.

SEASONAL DEVELOPMENT AND DIAPAUSE

Eriophyidae and Diptilomiopidae in temperate regions

In the simple or direct life cycle in which there is only one type of female, males and females are produced throughout the year. Both sexes begin their respective reproductive functions shortly after shedding the nymphal skin and die shortly after completing reproduction. Many bud inhabiting and leaf gall forming Eriophyidae fall into this category. Leaf gall mites in this category (e.g., the pear leaf blister mite, Eriophyes pyri (Pagenstecher)), spend the dormant season in live buds of their hosts, reproducing as temperatures allow, then inducing blisters on young leaves and reproducing in them the following growing season. Species that occupy a variety of niches on broad-leafed ever- green plants also reproduce virtually uninterrupted in this fashion. Thus, for both the citrus bud mite, A. sheldoni, and the citrus rust mite, Phyllocoptruta oleivora (Ashmead), reproduction continues throughout the year as conditions allow. The adult life span and reproductive period may be lengthened and senescence delayed by suboptimal temperatures.

In the second type of life cycle deutogynes or secondary females occur. These emerge in partial reproductive diapause, oviposition being delayed for sev- eral months until the host plant resumes growth the following spring. Deutogynes of Tegonotus aesculifoliae (Keifer) and E. emarginatae produce both sexes upon emergence from winter diapause (Keifer, 1942; Oldfield, 1969). Other leaf vagrant species known to diapause as overwintering deutogynes in- clude A. schlechtendali (Herbert, 1974; Easterbrook, 1979; Sapozhnikova, 1982; Kozlowski and Boczek, 1987), Epitrimerus pyri (Nalepa) (Easterbrook, 1978; Herbert, 1979) and Vasates quadripedes Shimer (Hall, 1967a). In addi- tion to E. emarginatae, the leaf gall mite E. laevis (Shevchenko, 1957) and

Manson and Oldfield 179

leaf erineum mite Aculus (formerly Eriophyes)leionotus (Nalepa) (Sokolov, 1986) produce winter-diapausing deutogynes. In these species deutogynes often first appear soon after summer solstice and comprise part of the female popu- lation of each succeeding generation. Owing to the departure from the leaves of deutogynes produced throughout much of the growing season, diapause in at least a portion of the population of many species amounts to aestivo-hiberna- tion which may last for more than six months.

Little evidence exists that multivoltine species produce deutogynes during the first spring generation (i.e., directly from overwintered deutogynes). In the extreme case of the univoltine species E. emarginatae, deutogynes produced di- rectly from overwintered deutogynes remain in diapause from the moment they emerge from the nymphal skin shortly after the summer solstice until the fol- lowing spring (Oldfield, 1969). In multivoltine species, newly produced deuto- gynes differ from contemporary protogynes in that they feed for some time then leave the feeding site and journey to another part of the plant, often bark crevices, bud scale scars or dried buds. Here they sequester themselves, often tightly packed in large groups, and become immobile for several weeks or months. This period in the life of deutogynes constitutes a physiological and reproductive diapause which ends at about the same time as the termination of dormancy of the host plant. Diapause is completed as growth of the plant is resumed in the spring, i.e. deutogynes become reproductively mature and lay eggs - some fertilised from sperm stored through diapause in the spermathecae and developing into females, some unfertilised which develop into males.

Pre-hibernat ion inseminat ion Early evidence that deutogynes are inseminated prior to overwintering was

provided by Putman (1939) who observed that A. fockeui produced only males reared from the nymphal stage in isolation, but overwintering females (deuto- gynes) produced both sexes of progeny before any spring progeny matured. Oldfield and Newell (1973) provided direct evidence of pre-hibernation in- semination of A. fockeui by observing visitation of spermatophores by newly emerged deutogynes and detecting spermatozoa in the spermathecae of deuto- gynes found in the fall on mature leaves and in hibernaria.

Population development Newly invaded buds may develop populations of thousands of eriophyoids

during a single growing season as exemplified by Cecidophyopsis vermiformis (Nalepa) (Krantz, 1979) and Eriophyes inaequalis Wilson and Oldfield (Old- field, unpublished). Leaf galls initiated at the start of the growing season, of- ten by a single deutogyne, may harbour a peak population of about 50 first gen- eration progeny, in the case of the univoltine species E. emarginatae, or more than one generation may develop within the gall so that the population is much higher. Hoyt (1969) found two peaks in the seasonal population trends of A. schlechtendali in Washington State, U.S.A., with the highest peak in June or July when numbers sometimes reached 2000 mites per leaf.

Deutogynes of Ep. pyri may number as many as 500 in permanently dormant buds (Easterbrook, 1978). Kozlowski and Boczek (1987) found deutogynes of A. schlechtendali in 10 distinguishably different sites on old apple trees and re- ported the highest numbers from under the edge of bud scales; higher survival occurred among deutogynes congregated in higher numbers. Living motionless throughout the dormant period of the plant, no reproduction occurred in deuto- gynes brought to the laboratory and placed on fresh leaves at various times during the dormant season until late January at the earliest. Schliesske (1984) reported that deutogynes of A. fockeui brought into the laboratory during win-

180 Life forms, deuterogyny, diapause and seasonal development

ter, become active but never reproduce. Mortality among diapausing deutogy- nes of A. schlechtendali ranges from 25 to 50% and a further 30-36% mortality occurs after diapause ceases and migration to new growth occurs (Kozlowski and Boczek, 1987). Spring migration occurs during several weeks from bud burst to petal fall. Easterbrook (1978, 1979) reported that deutogynes of Ep. pyri and A. schlechtendali produced protogynes and males, but succeeding generations of protogynes produced males and both types of female. Under laboratory con- ditions, the two species required similar lengths of time to complete a life cy- cle, ranging from about 5 weeks at 10.0~ to 9-10 days at 22.0~ By August, 45% of the females of Ep. pyri found on the leaves were deutogynes. Krantz (1973) reported that deutogynes of Aculus comatus (Nalepa), produced in small num- bers as early as May in Oregon, U.S.A., differ behaviourally from protogynes. Only protogynes, disseminated by wind in the field, were trapped during late June when deutogynes are already plentiful on the leaves. The continued per- sistence and increase of populations of A. comatus varied between growing sea- sons. In especially hot dry years, leaves dried earlier, became leathery, and populations plummeted early. Krantz suggested that a decrease in populations under these conditions may relate to the production of leaf cuticle with higher wax content in some plants as reported by Skoss (1955), which may preclude successful feeding, especially by immatures.

Effect of photoperiod Developmental time for A. schlechtendali appears unrelated to photope-

riod, as the period from egg to adult varied only slightly in populations reared at 24.0~ and 80-90% rh under total light, or 16, 12 or 8 hours of light per day (Schliesske, 1984). Sapozhnikova (1982) studied the effects of photoperiod on the tendency of each generation of A. schlechtendali from Leningrad, Russia, to produce the diapausing deutogyne form. The result was a seasonal variabil- ity of reaction to various photoperiods, and the potential to diapause at dif- ferent photoperiods was seen as an adaptation to variable environments.

A reported case of reproductive diapause in the grass-infesting species Ace- ria tulipae, among females that were identical to non-diapausing females (Sapozhnikova and Sukhareva, 1970) is especially interesting in light of re- ports of migratory forms in this species (Somsen, 1966) and a closely related species, Aceria saccharini (Walch), found on sugarcane (Mohanasundaram, 1981).

Tropical Eriophyidae

Relatively little is known about seasonal development of er iophyoids found in the tropics; however, the interesting case of the mango rust mite, Metaculus mangiferae (Attiah), represents the first case of obligatory ovo- viviparity and may signal ovoviviparity as a mode of reproduction common to other tropical species. Females of M. mangiferae produce 1-3 larvae daily af- ter a preoviposition period of 2-3 days, and a generation may be completed in as few as 6 days (Abou-Awad, 1981). Hibernation was reported to take place "under the scale leaves of buds" but the specific forms which overwinter were not mentioned. The observation of feeding symptoms on vegetative buds sug- gests that the mites do not pass winter in Egypt in diapause.

In another mango eriophyid, Cisaberoptus kenyae Keifer, the deutogyne is said to aestivate as an inactive form for a month or more during the growing season and thus may represent a diapause-form specialised for weathering suboptimal summer conditions.

Manson and Oldfield 181

Phytoptidae

Phytoptid mites exhibit a variety of means of diapausing as yet unreported for other eriophyoids. Sierraphytoptus alnivagrans Keifer, a leaf vagrant of Alnus species, forms morphologically different deutogynes which overwinter much the same as deutogynes of many eriophyid and diptilomiopid leaf va- grants (Jeppson et al., 1975). In Phytoptus avellanae (Nalepa), a species which causes swelling and retardation of buds of filbert, immatures constitute the spring migratory form and travel from infested, blasted axillary buds to new buds. There they move into core tissue and remain in a quiescent state (presumably diapausing) until mid-June when moulting to the adult instar commences. Swelling of buds invaded solely by this species commences only when newly emerged adults begin to reproduce during the summer; swelling continues throughout late summer and fall. On filberts, swelling of subterminal and terminal buds earlier in the season is caused by the eriophyid, C. vermi- formis. Adults of this species migrate during spring and, unlike P. avellanae, immediately increase populations after invading core tissues of new buds (Krantz, 1979).

Two species of phytoptids from conifers exhibit quite different means of di- apause (see also Chapter 1.4.4 (Boczek and Shevtchenko, 1996)). Trisetacus bagdasariani Bagnjuk (1984), found on Abies sibirica in Russia, produces two generations each year and diapauses in the second generation as nymphs. Another phytopt id , Nalepella haarlovi Boczek, infests needles of Picea abies, upon which it overwinters exclusively in the egg stage; all other instars disappear before the end of November (L6yttyniemi, 1971). Diapause-eggs are laid by females of the last two generations from late August through September, but only a few of t h o s e - laid by the next to last genera t ion- dia- pause. Eggs taken to the laboratory from the field earlier than late December never hatched, indicating that they require a specific exposure to cold to break diapause. Nearly half of those collected at the end of December and all of those collected after early January hatched. In the field, the majority of eggs survive until spring. Diapaused eggs taken to the laboratory hatch after 17 days at 10~ 10 days at 15~ and 7 days at 20, 25 or 30~ In Finland, 4-8 gen- erations are produced depending on the location. L6yttyniemi reported that he observed egg diapause in other eriophyoids infesting needles of conifers but did not identify them.

CONCLUSION

Only a comparatively few species of eriophyoids have as yet been studied in any detail, but those that have emphasise the variability in structure and life cycle of the different species. Our knowledge of the deutogyne form is greatly enhanced and it would seem these are more numerous than once was thought. New species continue to be described at a high rate, but there is obvi- ously a need for further careful detailed studies into morphology and life cy- cles. This is time-consuming, but the results would surely make it worthwhile. In many instances, immature stages have not been described or studied. Tropical forms need more study, particularly as the deutogynes of some species differ so markedly in form and function from those of temperate climates. Mites of the family Phytoptidae exhibit a variety of means of diapausing, not known in other families of Eriophyoidea. Further investigation is desirable. Some information is available on the effects of photoperiod and temperature,

182 Life forms, deuterogyny, diapause and seasonal development

but more precise studies of the effects of these factors on a greater variety of er iophyoids are urgent ly needed.

R E F E R E N C E S

Abou-Awad, B.A., 1981. Bionomics of the mango rust mite Metaculus mangiferae (Attiah) with description of immature stages (Eriophyoidea: Eriophyidae). Acarologia, 22: 151- 155.

Bagnjuk, I.G., 1984. A new bud mite (Acarina, Tetrapodili), the pest of the Siberian fir (Abies sibirica). Zool. J., 63: 373-382.

Boczek, J. and Shevtchenko, V.G., 1996. Ancient associations: eriophyoid mites on gym- nosperms. In: E.E. Lindquist, M.W. Sabelis and J. Bruin (Editors), Eriophyoid Mites. Their biology, natural enemies and control. Elsevier Science Publ., Amsterdam, The Netherlands, pp. 217-225.

de Lillo, E., 1991. Preliminary observations of ovoviviparity in the gall-forming mite, Aceria caulobius (Nal.) (Eriophyoidea: Eriophyidae). In: R. Schuster and P.W. Murphy (Editors), The Acari - Reproduction, development and life-history strategies. Chapman and Hall, London, UK, pp. 223-229.

Easterbrook, M.A., 1978. The life history and bionomics of Epitrimerus pyri (Acarina: Eriophyidae) on pear. Ann. Appl. Biol., 88: 13-22.

Easterbrook, M.A., 1979. The life history of the eriophyid mite, Aculus schlechtendali on apple in south-east England. Ann. Appl. Biol., 91: 287-296.

Hall, C.C., Jr., 1967a. A look at eriophyid life cycles. Ann. Entomol. Soc. Am., 60: 91-94. Hall, C.C., Jr., 1967b. The Eriophyoidea of Kansas. Univ. Kansas Sci. Bull., 47: 601-675. Hassan, E.F.O. and Keifer, H.H., 1978. The mango leaf-coating mite, Cisaberoptus kenyae K.

(Eriophyidae, Aberoptinae). Pan Pacific Entomol., 54: 185-193. Herbert, H.J., 1974. Notes on the biology of the apple rust mite, Aculus schlechtendali

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