THE BIOLOGY OF THE BROWN ORCHARD 1.fi1E , BRYOBIA ARBOREA RGAN AND ANDERSON (ACARINA ' TETRAN'reH:fl)AE) ON STONE 'RUIT TREES L\1 THE DALLES, OREGON AREA

EVERETT C BURTS

A THESIS

submitted to

OREGON STATE COLLEGE

in partial fulf'illment of the requii'ements for the degree of

~lASTER OF SCIENCE June 19$7 IPP$O!E}r

Redacted for Privacy

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D.E of, Srrdurtr gohool

Drt t[.dr frpram@ IyE A by S$il Dra Bur** ACKNOO.EDGEMEN TS

The writer is deeply indebted to his major professor, Dr. Charles H. artin, Associate Professor of Entooology, for his guidance and encouragement in both the planning of the problem and the pre.. paration of the manuscript.

The writer is grateful to Mr. Walter Mellenthin, Superintendent of the Mid-columbia Branch Experiment Station, for allowing him to use the facilities of the experiment station in carrying out the studies. 'lhe writer wishes to acknowledge Dr. Paul o. Ritcher, Chaiman of the Department of Entomlogy.. and Dr. Frank H. Smith, Professor of Botany, for their helpful criticisms of the manuscript, and for serving on the graduate coDillittee.

The writer is also deeply indebted to his vi.fe, Willow Dean Burts, for typing the manuscript and tor her faith and encouragement. throughout the past three years. 'fo Edward w. Anthon, who did so lllUch to •ke ~ college education possible tABLE OF CONTENTS

PAGE

INTRODUCTION ••••••••••••••••••••••••••••••••• ~•···~··•••••·•••••••l . SYSmMA.'l'IC HISTORY OF BRYOBIA PRAETI SA KOCH AND BRYOBIA ARBOREA !IJRGAll .AllD AN'DERSON •••• • ...... 2

Family' Tetranychidae; ••••••••••••••••••••••••••••••••••••••••2

Sllb.fazni.l.)r Br)tobi.mae••••••••• -· •• ·• •• -· ••••..••.•.••••••••••• .••• •3

1'ri[)e .B!".Yobiin.i•••.• • . •• ,. . • • ••• •·• • . •• . •• •. • • • •• • • • • • • • • • •• •• . •.3

GenllS Bqobia•...... • •• •• •• ..... • •• • •.) The Br;yobia praetiosa °Complex"••••••••••••••••••••••••••••••4

Bl'l'obia ax-bo~ea • •••.••••••.••••••.•.••••••••••••••••••••••••••S Description of Forms . ,•••••••••••••••,•••••••••••••••••••••••••6 Common Names ••••••• , •••••••••••••••••••••••••••••••••••••••••9

Dis1ix'ibution••.•••••••• • ••••••• • ••••••••••• • •••••••• • •••••••••9

METHODS AND -TEltiA.IS •••••.••••••• ., •••••••••••••••••••••••••••••••10

Collectin.g•• ••••••.••••••••••••••••••.•••••• .- ••••••••••••••••10

.MOunting and Staining••• - •• •••••••••.,...... ••• ••••••••••••10 Rearing •••••••••••••••••••••••••••••••••••••••••••••••••••••l2

Re&r'irlg-si'te ...... •••••••••••••••••••••••••••••••••••.•1,$ COllecting and Processing Temperature Data••••••••••••••••••l$ Orchard Observations...... l6

THE RELATIONSHIP OF TEMPERATURE TO DEVELOPHENT OF THE BROWI ORCH:Alm lfi"m••••• • ••• • ••••••• • •••••••• •• •••• ·• ...... • ••·•. • .17

Th.e Egg Stage ~ . •. • • • • • • • • • • • •• • • •·• • • • • • • • • • • • • • • • • • • • • • • • • • • .18

Termination of Diapause in the OVerwintering Egg ••••••••••• ~lB

~ ]mmature Stages •••••••••••••••••••·······~····••••••••••20 Discussion of Results••·• ••••••••••••••••••••••••,•••••••••••,.21 IAmgtb of Generations in the Inaectary...... •.• •• •'• •••••••2S LIFE HIS'fO.RI AND HABITS•••••••••••••••••••••••••••••••••••••••••·2S overW1n.terins., ••••••••••••••••••••••••••••••-••• • •••••••••••26 De'Velopment of the Firat Generation••••••••, ...... 27

Hatching of the overwintering egg•••••••••••••••, ••••••27

l.a&z':V'a...... ~ ...... 28 Ecdy'aia••••••.••, ...... 29

.Pro~...... •·...... )0.

Deuto~··•••••••••••••••••••••••••·~·•••••••••••••••)l Effeot of teq;,erature on development or the innature inatara•••••••••••••••••••••••••••••••••••••••••••••••)l

Ad:ul.t •• .••••••• •.• ...... tt ••••••••••••••••••••••••• ·32 SUIIIDer Generations•••••••••••••••••••••, •••.•••••••••••••••••))

S~inter Egg DepoaitioD••••••••••••••••••••••••••••••••JS

Feeding and Migratin&•••••••••••••••••••••••••••••••••••••••J6 Seasonal Abund.ance and Damage to the Boat Plante••••••••••••,38 Boat Plata•••••••••••••••••••••••••••••••••••••••••••••••••)9 H&tural Cont.rol•••••••••••••••••••••••••••••••••••••••••••••40

SUMMABI•••••••••••••••••••••••••••••••••••••••••••••••••~••••••••4l BIBLIOGRlPHI•••••••••••••••••••••••••••••••••••••••••••••••••••••4S

APPENDII..•. • • • •. • •. •. • • • •• • •. • • • • • • • • •-• • • • • • • • • • • • • • • • • • • • • • • • • • .49 THE BIOLOOY OF THE BReW ORCHARD , BRYOBIA ARBOREA M)RQAN AND ANDERSON (ACARINA: TE~) ri . STONE FRUIT TREES IN THE DALLES, OREGON AREA

INTRODUCTION

With the beginning of the wide spread use of DDT for insect control on agricultural crops, phytophagous rapidly bacame one of the major groups of plant. pests. Since that time, and especial.ly since the appearance of resistance of the two-spotted mite, Tetratgehus telarius (L.), to organic phosphate insecticides,

there has been a continual effort on the part of industrial and governmental research workers to develop more .efficient materials

for the chemical control of these pests. Knowledge of the life history and habits of thes pests would add considerabq to the

e.ffioiency of the control programs . 1he purpose of the work

reported here is to help fill this need for information on the

biology of one species of phytophagous mites, the brown orchard mite, Bryobia arborea Morgan and Anderson.

'!he data presented in this paper on the brown orcha.Td mi.te were gathered during the past three years in The Dalles, Oregon

area. 1he o'bservations and experiments were carried out in orchards of the area, as well as in an insectary. The studies were directed

towards obtaining information on the life history and habits of

the mite in relation to the factors of its enVironment. In the

first section the of the brown orchard mite and the descriptions of the various instars are presented in considerable 2

detaU. 1h1B seemed advisable because of the taxonomic con.i\J.Bion

111thin the group. In the second section the methods and matenala used in the studies are presentec:l. The writer believes this to be justified because eo little has been published on •thods for studying the biology of ph1topbagous mites.- A third section of this paper tntats the relationship of tbe dewlopment of individuals to temperatur.. The final section presents in.tomation on the life history and. habits of the mit'A) as observed 11'1 orchards of the area•

SYSTEMA.TIC HISroRY OF BRYOBIA PBAETIOSA KOOB AND BRYOBIA ARBOREA !'DRGD ~

1he data reported in this paper are the results of studies of B!"j2bi& arborea Horgan and Anderson. Comparative. morphological studies o£ Bqobia arl»rea and Bqobia praetiosa Koch are used in describing the systematic history of these two species.

Fam.il3 Tetranychid.ae Donnadieu 187)

b name Tetranychid&s vas first pro.posed by Donnadieu in l87S at "the suprageneric lev.tl• He included many species of ~ Bapbignathidae, Pbytopt1palp1dae and Tuckere111dae in the Tetrarq­ cbid&s. S:I.Dce that time this taxon has been raised and llm1ted. lDltU today it inc~udea only those prostigmatid Ddtes having the paired basal segments of ·the chelioera fused into a pouch•lilce

.lobe (called a .stylophoN) within which are anchored the curved

* The classi£1cation followed here is that of Pritchard and Baker (8o, p.4). .,

l proximal ends of the movable stylets. They also have a strong

"claw" or "thumb claw" process on the fourth palpal. segment.

This family contains the true "spider mites".

The family Tetranychidae is divided into two subfamilies,

Bryobiinae and Tetranychinae. Bmbia a:rborea and ]!.• praetiosa be]Dng to the sub£~ yobiinae.

Subfamily Bryobiinae Berlese 1913

The subfamily Bryobiinae contains the l!X)St generalized members of the family. None of the species is !mown to produce webbing or silken threads. 'Ihis subfa.Jnil3 is characterized by having well developed true claws, glomerate, elongate or sacculex terminations of tbe peritremes and duplex setae placed at the abruptly declivate distal end of the tarsus (.30, p . l2).

Tribe Bryobiini Reck 19.52

1'be tribe Bryobiini is characterized by Pritchard and Baker

(.30~ p . l4) as having four pairs of dorsal propoclosoma:ts,. the true claw developed. as a curved. book or a long pad with lateral tenent hairs, and twelve pairs of dorsal hysterosomals.

Genus Bry;obia Koch 1836

'lhe Bryobia .includes those m1tes which have the true claw \Ulcinate and with one to several pairs of mediolateral tenent ha1rs. 4

The ~obia praetiosa "Complex"

Pritchard and Baker list 19 name~ as ,synonyms for Beyobia praetiosa. To add even more to the confusion of the group many of the describers failed to presei'Ve t'pes and their descriptions

and illustrations are not suffioiently•clear to establish positive

identifications. Later workers (1.91 pp. l.30· 1.35) found that the life histories and habits of the ndtes from various areas were different, and that even within given areas populations were found on different hosts which would not inter- transfer. Mathys (191 p . l.41) lists four distinct races or biot3pes1 separated according to host plants and life history, one of which occurs only on fruit trees, one on gooseberry, another on iv,y and a fourth on a number of herbaceous plants, including many legwQes and grasses. Of these four, at least the fruit tree type and the legume-grass type occur in North America.

According to Pritchard and Baker (.301 p. )O) mites of the Beyobia praetiosa "co plextt may .be differentiated from other mem­ bers of the genus by the presence of strong anterior propodosomal projections, and an empodium in the adult consisting of a single pair of tenent ·hairs. '!be dorsal setae of the body are short and broadly spatulate. Males are unreported in the literature.

lbe taxonom;r of the Bryob1a praetiosa ttcomplex'' has long been confused. Because the mites of this complex are entirely partheno­ genic~ they cannot be separated into species on the basis of reproductive isolation. ~til recent]Jr the morphological Obaracters had not been thoroughly examined and tmderstood. For

this reason it has long been a controversial group for the "lumpers"

and the "splitters". 'lhe l'\llTi)ers based their classification on

the similar:l.ty of m:>rphol.og:ical characteristics, while the splitters

used the vide variations in host plants and life histories as a

basis for their separations.

Within the past few years rgan and Anderson 1n British

ColUlllbia, following the leads of Venables (40, p . 31) 1 have made

a thorough stu.dy of the biology of the "tree" form and "herb"

form as they occur in that area. They found not only differences

in the l.if'e histories and habits (1, pp. l-46), but also morpho­

logical di!'ferences {24, p . l4) which distinguish the two t)'pes

clearly. '!hey have divided the . complex, as it occurs in their area, into two separate species. lhe name Bryobia

arborea rgan and Anderson is used for the tree form. !_. praetiosa refers to the herb form.

Bryobia arborea rgan and Anderson

1he name Bryobia arborea is at the moment a manuscript name proposed by rgan and Anderson of British Columbia to refer to those indiViduals infesting trees, while ! • praetiosa is used for those ind1viduals infesting herbaceous plants. Pemission has · been given to the writer by iorgan and Anderson to use their key

(24, p . l4). This thesis does not constitute publication, so the n is not validated here. 6 Key to Bryobia praetiosa Koch and ! . arborea M:»rgan and Anderson

n••.foreleg greater than o.69 mm. lon~u body length greater than 0.74 mm. long; lateral distance between bases of anterior pair of dorsocentral hysterosomal setae (DCl) greater than 0.10 mm. :tarval setae lanceolate, unlike those of adult . (Fig. lA); lateral distance between bases of 001 approxi­ mately. four times length of seta•••••••••••••••••. •praetiosa. "Foreleg less than 0.69 • long; body length less than 0.74 mm. long; lateral distance between bases of nc1 less than 0.10 mm. Larval setae foliaceous, like those of BdUlt (Fig lB); lateral distance between bases of DC1 approximate~ twice length of seta.••••••••••••••••••••••••.•••.• ,• •••arborea sp.n." The writer has compared specimens of the two species of

BrYt?bia in 'lbe Dalles area, with the unpublished descriptions of

~rgatl and .lmderaon, and with represent.ative specimens from British

Columbia. The writer was able to separate the two forms in The

Dalles area w1th the key and descriptions of li:Jrgan and Anderson and to match them with the specimens furnished by N• H. Anderson

{24, p.l4). The writer's determinations have been verified by

N. H. Anderson and several specimens have been filed in the

CQllection of the Department of Entomology at Oregon State College.

Description. of Forms

Since Koch preserved no types, and because his descriptions and illustrations are not sufficiently clear for precise indenti­ fication, McGregor in 1950 (211 p.365) redescribed Bryobia praetiosa which at that time included all of the 19 species in the complex •

. His description is as follows:

"Female. Color reddish-brown to darker, at times with a 7

greenish tinge. Body from ab:>ve broadly oval, somewhat flattened dorsal.ly, noticeably truncate ea · • Striations on dorsum irregularly tortuous. Body proper a ve with l4 pairs of spatulate to foliaceious setaeJ 2 each side submargin­ ally behind coxae II; 8 each side near margin of abdomen from humeral angle to caudal ·end; a tranaverse series of 4 setae just behind main dorsal "uture; 2 pairs of submedian setae near center of alxlo,nen . Cephal.othorax anterior~ bearing a free plate between coxae I , which is distinctly 4- lobed1 each lobe dietal.l..,y bearmg· a foliaceous seta• Two eye comeae each side over and behind coxae II. Frontal tracheae termina­ ting external:cy in teatlike tubes. Mandibular plate ob:>vate, sollle11hat notched in front. Forelegs as long as, or longer than, body; other legs shorter than body, legs II the shortest; setae of legs from llnear-lanceolate to seiTateclavate. All tarsi bearing 2 strong class. Tarsus I dorsally with 2 sets of duplex setae, proximate. Seventeen or 18 setae borne proximad of prox:i.mal set of duplex setae. Onychium I with a long tenent hair borne each side near middle of each claw J a median pulvillus bearing 2 similar hairs• Tarsi II- IV each with pulvillus bearing pectinate series of tenent hairs. Last segment of pal.pus borne ventrally from preceding segment which bears a stout claw dorso-terminal.ly] "thumb" subcylind... rical, aring apically a stout, lanceolate seta, and 6 addi· tional setae on 1ts distal half. Relative lengths of seg­ ments of legs I as follows: Trochanter, 2; femur1 29 .t patella, ll; tibia, 22; tarsus, ~6.

" The larval stage differs from the adult female as follows; The dorsal body setae are not leafllke1 but are lanc,eolate to clavate, and conspicuously setose; the protruding traebae are bosslike; the free., cephalothoracic plate is lacking, but is replaced by 4·rolmded protuberances, each bearing a lanceolate, pilose seta.

II Egg globular, red. tt

In describing Bryobia arborea, rgan and Anderson use

~~tiregor •s description as a basis. Their description reads as follows (241 p.l5)a· "Female : In general appearance very similar to praetiosa as described by McGregor (8}., but smaller in size. BodY length o.SSl to 0. 731 mm . ; 'l.xxiy width 0.348 to o.$27 mm.J foreleg {excluding coxa and tarsal claws) o.$4.3 to 0 . 659 mm• . (50 specimens} . Lateral distance between the bases of the paired dorsocentral hysterosomal. setae; nc1, 0.047 to 0 . 084 •J DC2, 0.027 to 0.061 •i DC.3 1 0.020 to 0.044 n'm . {20 8

specimens)•

11 Malec Does not occur. Species entirely parthenogene­ tic.

11 Larvac Similar- to praetiosa as described by McGregor (8) but body setae foliaceoue like those of adult (not lanceo­ late to clavate as in ~raetiosa). Body length 0.172 to 0.19.3 mm.; body width .l4j to 0.164 mm. (20 specimens). Lateral distance between the bases of the paired dorsocentral hysterosomal setae; DC11 0.0.3~ to 0.0~.3 mm.J IX12 1 0.017 to 0.0.30 mm.; DC,3 1 0.01.3 to 0.022 mm. (2~ specimens). "tgga Spherical, slightly nattened at base. Sizea 0.1.36 to 0.178 mm. diameter (~ specimens)."

In examining specimens of !• arborea collected in The Dalles area, the writer has observed the following additional clifferences from the descriptions of MdGregor and of rgan and Anderson. The I. peritremes (called •trontal trachea" by cpregor) appear to have a perforated teat-like knob which is partially hollow, (Figure VIII)J color of the adults vary from an orange-bt·own or tan in specimens which had not fed after moulting, to a dark green in .fully fed specimens. Newly hatched larvae are scarlet-red in color, changing to a dark olive green after f eeding; their peritremes have a bifurcate knob, the outer fork being longer and curved inward

(Figure VIII)• The writer has not found any descriptions of the two nYll!Phal instars of !!• e-aetiosa and. ~ · arborea in the literature. Since the various instars must be identified in the course of biological studies, the writer is describing these stages as follows c

Deutonympha Similar to the adult female in general body shape and

color, but differing in size, relative length of the \

9 forelegs, and shape of the peritremes.

Body length 0.48 to o.S9 mm . J body width 0.39 to o.so

mm. J ratio of body length to leg I, 1.49 to 1.?3al.

the peritremes end extern~ 1n a loop with an extra

knob on the mesal edge of its base (Figure VIII).

Protonympha Similar to the deutonymph1 but differing 1n size,

relative length of foreleg and shape of peritremes.

Body length 0.37 to 0.4? mm.J body width 0 • .)~ to

0.38 mm.1 ratio of body length to leg I, 1.73 to l.8Jl•

The peritremes end external.ly in a loop with a knob on the dorsal side of its base (Figure VIII).

Co:rmnon Names

Anderson and :Drgan (11 p.2) list 16 common names from the

literature for the Bqobia praetio.sa complex. Of these, the

mite, the brown orchard nlite and the brown al.Ioond mite are

probably the most wiru,;ly used in western North America. In much of

the literature, the name clover mite has been used for both the tree and herb forms. Throughout this paper the tree form, B!7obia

arborea Morgan and Anderson, will be referred to as the brown orchard

mite.

Distribution

Bryobia arl:orea MOrgan and Anderson appears to be cosmopoli­

tan in distribution, rut since this species has only recently been lO recognized, it is included in !• praetiosa in all the literature. The tree form of !• praetiosa has been reported from North and South

~rica, Europe and Australia (91 p.l40; 101 p.4.56; 19, p .l38 and 40, p.4l). AlSo it probably occurs in Africa and Asia as there

are numerous reports of ~. 12raetiosa from these areas, some including

forms living on deciduous trees.

METHODS AND MATERIAlS

Collecting

Specimens of Bryobia arborea used in life history studies in

the insectary were collected from peach and cherry trees by bring­

ing portions of the in.fested plants into the laboratory and removing

specimens from them. 1he li.ving mites were mved from place to

place by means of a small, number one, dry camel hair brush. Specimens of ! • praetiosa used for n:orphological studies were

collected from herbaceous plants in the same manner or were collected from Berlese funnel samples of trash gathered from arotmd tree

trunks and bnj Jdjngs.

)t)unting and Staining

Specimens of roth !!• arborea and !• praetiosa were mounted on slides for comparative study and for the preparation of drawings.

Mites were removed .from the host with a small teasing needle and placed directly into a drop of momting medium on a glase slide.

The teasing needle was made by sticking a minuten insect pin into ll

the enci of a small glass roci softened in a gas flame.

'!he specimens were mounted alive. ·fh1a 111ttbod proved better

than collecting in alcohol and mounting later, as it required less

ba\dl1ng ot the specimens and prounta. Alcohol

teDd.ed to harden the speci.Mns and rendencl them difficult to

clear. 'lbe best result& were obtained when only one epecimen vas placed on a al.i&l. '!he best mounting medium for tb.e brown orchard. mite proved

to be Boyer•a, a modified Berlese aolution, described by Pritchard

and Balcer (.30, p.2). SWnjng vas especially necessary for larval

•cimana• because they often cle~ed ao completelY~ to be almost invisible UDder ·tbe micl'Oaaope. 1b1a was done by add:!ng a fev

crystals of picric acid to the stock bottle of Hoyer 1s Dllldi:wa.

T.he C178tal.a saw the adium a very trlnSp&l"ent yellow cast•

.Utbough a.l.Jmst unnot1ceabl8 in the ll*iium, the exoak8leton of

the mites vas aWned conaiderabl¥1 and the color did not fade with till-.. 2be frelih slides vere placed in an oven at 5SO c to claar the

apecimeDIJ. 1'he time required for cle~ing the m1tes varied vith

their stage of developMnt and the amount of bJxnm. p1gment in tMir

bodies. NevlJr batch$d nymphs were cleared in 24 to 48 hours1 vh1l.e it vas necessa:t'7 to leave adult apecimans in the oven for a

week or 10 daya. 'lhua the slides bad to be checked !rom time to

tiM and. reu.)Ved from tbe o~ when the spec1ana were properly

~leared, S9me clearing occurred ,after the, ~iides . were . ~emoved .. from the oven.

Mites were reared in individual cages so as to maka possible

df.ily obeervations on their developmental progress. Individual

. specimens were reared in tbe insectary by placing them ill small

cage• .t~ clamped to tbe eurface of the leaf of the boat plant.

Spr:l.ng•type Wooden olotheapins were the bases for these cages,

wbicb were oonstzucted as t'oll.ovs 1. A 3/UJ inch hole was drilled

in one J• of a clbthespill about ')/8 inch from the end. The inner

surfaces ot' both j811s were then ground with an emery wheel until

they were 8lll00th and t'it together evenly Vben the clothespin vaa

olosecl. The jw with the bole bored in it was ground with an

.-ry llbeel on the outer ~ace untU it was smooth anci parallel with the :t.nner surface. Tbe jaw rema1.ni.ng was about l/8 inch

thick. A piece of ethyl acetate l/2 inch square was glued. w1th

bal.88Dl to the outer surface of the jaw so that it made a window

o'VU' the bole. A piece of felt weather stripping was glued. to the

~ surface of the other jaw, and the glue was allowed to dry.

After some practice these cages could be quickJ¥ and precise~

constructed. Eadl cage was identified by a number written on it vith pencll.

1be cages oould be used ovw many times. After each use the

. pl..utic window was removed and the cell cleaned by' eand.ing it with

fine sanc,ipaper roll.ec1 into a rod. UU.s reDI)Wd lillY eggs, debris or dead mites which might confuse observations during the next use.

'lhe requirements of a good cage are: to confine individual mites in as nearly normal conditions as possiblej to allow quick and easy manipulation of the mite in and out of the cage. The cage described above met these requirements better than any of the others tried. The br01m orchard mite, as a transient feeder, mows back on to the wood or bark or the plant after feeding to moult and to deposit its eggs. The clothespin cages provided the wooden surface for these activities. The felt on the lower jaw of the cage served as a cuzshion for the leaf and held it firml.y against the upper jaw, to prevent the escape of the mite.

The cages were too heav.r to hang on the leaves of cherry ·and peach seedlings. To prevent the cage from damaging the host plant, a heavy wire was stuck into the soU at the base of the plant and bent at a right angle about one inch from the top end at the height of the cage. The bent end of the support was slipped through the spring of the cage so that most of the weight of the cage was supported by the wire. the host plants used for rearing Bryobia arborea were Mazzard cherry seedlings and I.Dvell peach seedlings. The cherry seedlings were obtained from Dr. J. A. Milbrath, Department o£ Bo .. Oregon State College. The peach seedlings were grown from seed at the rearing site. The two...spotted , Tetranychus telarius (L.)1 was a OODStant of these plants as no control measures could~ practiced vb1le the caged mites were on thea. Except for dauge to tbe foliage by the two-spotted spider mites, the host plalts were not noticeabl¥ affected by their m1te infestation and grew eatis:tactor:i.l¥. It iJ not known whether the feeding injury to the host plants by the two-spotted mite affected the development or the brcrtm orchard m1tee.

Observations with a stereoscopic microscope were made of the

:t.n41vidual mite in each cage. 1he position o! the mite 1n th• cage, ita activity, and ita "-'velopaantal progress were recorded

!be records were. kept on data sheets provided nth a amall, circle tor eaoh observation eo that the mite•• position could eae!l)' be cheoad 1n relation to that of the previous dq. 1b1s was.necessary

1n orde:' to tellwbetber the specimen was in an active or qtdesoent state.

The best method of lighting the cages during observations vas to fasten a l1gbt to the microscope eo that it was directea on the focal point of the objective.

Tbroughout DOSt of the rearing work, observations were lll&de by holding the microscope in one hand and bringing the cageB into toaua v.Lth the other. For this proceclure1 the base of the micro­ scope was removed at the sliding dove•t&i.l joint. 1be traM remain•

1ng vu used as a handle. Wh1.l.e making the observations it vas necessary to sit with both arms rested on the table so that the microscope and the cage could be held steadiJ¥. lS lel.l' the end of the rearing project another method of making the observations was tried vhicb vas far superior to that described above. A eupport with two shelves vas builtJ one was the same he18ht u 'the plant pota and a second was lt inches lower and ex... tended 'tlto. inches beyond the b'ont tklge of the first. 1be uppe:r abel! was macle of one by four boarcl, the lover shelf IZld the ends of one b.Y six 'boards. Tb1a tJUPport vas three feet long. A aeecl­

Ung oherr'y tr.e 1n a plant pet was bent over each end of the support and .tutened flat to the top abel£. i'be rearing ~·s were pl.aoecl on the le&vee eo that they too rested on the top shelt. ~ base of the microsoope vas then pushed between the ehelvea untU the cages were 111th1n focue1Dg range • 'lhe nlcroscope could. be eaa~ 110ved along the lower shelf until it was in line with the Proper cage. Ttm or 12 cages oould be set upon such a unit and. the ob8ervations could be ude quiokl;y -.nd accurateq.

1'be rearing vas do%18 in a nylon-screen enclDsed insectary.

'fhil &!forded. partial shade and shelter from the wind and rain; yet tiel not alter tbe environment as JIDlCh as a greenhouse. Temperatures in the shelter were usually 2 to 4 degrees higher than the outside air temperature llt tb8 uperiment station.

Collecting fllld Proceesing Temperature Data 16 and humidity at the rearing site. The instrument was kept inside

the insectary close to the rearing area. It wae placed in awn­ tilated wooden box to shield it from the direct sun. Tables of the

DIA'daua amd min1mum d&ily ~ratures and relative hum1clit1ea were made from the hygro-thermograph charta. 1'be mean t.eq,erature and relative hUDd.dit,y for each cia¥ were derived as the awrage of ~

M"dmum and the m1 n:lliDDle !he M&n temperatures for each of the days dlJX"ing the develop~MD.t.al period of each specimen were averaged,

8Dd this val13 vas used. as the average mean developmental. tuper&­ ture for the period.

!he data nre oondensed by grouping together individual :rear­ ing teste with ai.milar reaulte. Only data from the aaae season of the year were grouped together.

~ Obaervatione

'lhe biology of Bryobia arborea in the orchards of the am wu atud.ied by direct observationa on natural populations. Egg counts, population counts,. and checks on the seaecnal development were made by bringing twigs :froa infested oraharie into the laboratory whGre observations were made vith a binocular microscope. Samples were taken at seven to lO day intervals. Between 2,000 and 31 000 m1tea ve:re counted £rom each aamplAt. Counts were made on both leaves and tllfiga. Observations on feeding and migration habits were Jl8de 1n the orcha:rd vitbout diaturbing the mites. At the time the observa­ tionB of the mites were made temperature and humidity readings were 17 made with a sling psychrometer. 1hese readings were correl.ated with local observations on feeding and migrations.

SWIIllers and Baker ()7, p:p •.369•362} reported on a procedure for co1mting brown orcharcl mites on al.,nd. trees which invol'V8Cl beating twigs over a heavy screen or wire mesh to knock the m1tea onto a paper. 1tda •thod was tried at The Dalles, but maJlY of the Dd..tee in the quiescent stage were not knooked loose by verr seven beating ot ~ twiga agaiDst the mesh. For this reuon the method is not appli~blll to biological studies, espec1al:cy vbere relative nUIIlbere of various inetara are· need4tcl.

mE RELATIOWSHIP OF TEMPERATURE TO DEVELOPMENT OF 11iE BROWN ORCHARD MI'l'Jt

One ll8t.bod. of stuqmg the .t"tects of various enVi.ronmental f.-otors on the rate of development of organiaa is to con-elate obsel-ved rates of development of individual specimens with factors of the envii"onment u measured at the site of rearing. The reaulta irom in4ividual rearing are more accurate tban those obtained from obaervations ·of colonies or mass rearing studies. 'lhe7 alao lend tbem~elws more readlly to atatiatical ana]¥81s, so that a more thorough evaluation of the data can. be made.

l'l1 this section ~atu:re-d.evelDpment time relat1onahip8 obt&1necl from individual rearing tests of the ~1'01Bl orchard mite are discussed.. Recorda of relative humidit;y were &lao made, but t.be range of mean humidity at the rearing site proved not to be . s1gnificant. !~he diurtJ.al nuctuatione in relative humiditT wre 18

ae high aa 7S%1 but the mean relative humiditT val.ues outside the rearing cages for periods of a veek or longer were nearzy- the same

I during the two eeasons the testa were conducted. Mean relative htild dities 1n the insectary for ~rtods or 10 days fell w1thin a range of 6o to 7CYJ, from April to October.

1he Egg Stage

Because moat of the adulta kept in individual cages laid most]J' winter eggs, not much data are available tor the 8UJIIIIer egg stage.

1'he incubation period for s\UIIIDer eggs varied between eight and 17 d&~B 8hd averaged about one and one hal..f times longer than the larval stage at a given temperature. The incubation penods of 47 eggs were obeerved during the indiviclual rearing studies.

~r total of. 4375 winter·.eggs on 10 six..inch lengths o£ cherey twigs were collected in October and held for 105 dqzs at.. 41° F._to break their diapauae. After receiving the cold treatment, the eggs wre incubated at 70° F. '1be nUIIlber of larvae hatching from the eggs vas counted each dq. All the viable eggs hatched w1thin l5 ciqB inCUbation. }t)re than SO% ot the eggs hatched within seven dalW·

Termirultion of Diapause in the OVerwintering Egg

In the case of some insecta and mi.tes, diapause is terminated onq atter exposures to tulperaturea within a certain :range for a minjJNil period of time. Lees (l$1 p.4) states that in organiaa 19 with this type of diapause, there is a "diapause development•, which occurs only when temperatures are within a critical range.

Tests were conducted to determine the requirements for ter­ mination of diapause of the overwintaring eggs of the brown orchard mite. Ninety twigs six inches in length containing overwintering eggs were collected on October 10. Twenty of these twig samples were kept in a room at 70° F. to incubate the eggs. Separate groups of lO twigs each were exposed to 22° F. for periods of 48 hours . 1 30, 57 1 and 117 dqs. Similar groups o£ twigs were exposed to 41° F. f or 58, 105, and lSO days. Atter the cold exposure periods the twigs were kept at temperatures near 700 F. to incubate the eggs. The nl.1111ber of larvae hatching from the eggs was counted each day for each group until no more hatching occurred {Table VI).

A simple "cold shock" is probably not the factor responaible for the termination of diapause of the overwintering eggs of the brown orchard mi.te since there was a low percentage batch of eggs exposed to freesing temperatures for 48 hours and .30 days. Tempera. tures of 41° F. are more effective than temperatures of 22° F. in terminating diapause; regardless of the exposure time. Diapause was terminated in only about 8~ of the e.ggs exposed to 22° F. for ll.8 d&yc~, while }.()(:)% of the viable eggs hatched after 105 days exposure to 4l° F. '1'he writer did not determine whether the eggs exposed to 220 F. would hatch af'ter exposure at 41° F. for a suf.fic.ient time to break diapause; so a definite statement on the lethal effects of freezing 20

tuperatun cannot be made. Howe~, probably the freezing tempera­

tures did. not cause significant mortali'l;rJ' o£ the eggs. Eggs which

failed to batch after exposure to 22° I. remaj ned round and turgid.

during Hveral vaea• elq)Osure to 700 F.. The eggs receiving no cold

treat.ant &lao remained turgid for more than 150 d&7& at 7cP r. Temperatures of 22° r, or lover comonly occur ill 'ftle Dalles area during the winter. Nearly all tbe eggs vhioh reu.in tlll'gid and Nd. tbrougbgut the winter hatch the following spring.

Lha (14, p.47S) reported that tuperatures between 34° a4 bEJO 1 .. were nearly equal.ly effeotive in terminating diapawse of the overwintering eggs of Matatetr!&O}luas!!!!!! (:Koch}, the Europem red mite. Be also found tbat •treezing• the eggs at 2)° F. faUed to

break diip&uae) regardless o£ the length o£ the exposure period.

Be also states that low temperatwes vithin the range normal.ly occurring c:lur.l.ng the winter months seem to be the onl.T illlportmt envi.rolmental £actor in-volved in the termination of diapawse in

tbe Eul"'Pf'C1 nd mite.

!be :r.u.ture Stages

'1ba ruulta o~ in ind1vic:iual rearing testa tor the tem­ perature-developD*lt t.ime l"elationahips of the post-hatch stages of Bq!lxl.a arborea are presented in the appendix. Tables I, n, lli ancl IV list the data obtained for the temperature-development

U. rel,ationah~ps. 1he lines of least squares1 the regression coefficients IIDd the correlation coefficients are included. !be 21

l1ae of least squares is drawn in the graph of the temperature­ development relationships for the period trom eclosion to the adult

(Figure IV). The line of least aquares is not drawn in the graphs

of the temperature-development data for the individual instare

because there is insufficient data to accurate~ determine straight line relationships.

Discussion of Results

'.l'bere is a general tendency for the development-rate temperature data to group aroUDd a median range of temperatures. fhis occurs because the dai]¥ temperatures normally encountered. dl.lri.ni the sea­ son that the organism is active, form a normal distribution around

a certain mean temperature. lDwer or higher temperatures occur lesa frequently at increasingly greater deviations from this mean value.

Also of importance in the distribution of the data collected. under natural conditions is that more individuaJ.a tend to develop within

the JI8Ciian range of conditions.

In the course of the studies reported here, an average of 2$

rearing tests were maintained throughout the season when active

stages of the brown orchard mites occurred in the orchard.s of the

&l"ea. No atteq>t vas Jl&de to modify the temperature or to conduct

larger nliiilbers of tests UDder extrea temperature oondi tiona. For

this reason there are much more data within the intermediate ranges of temperature than at either extreme.

It baa been sbotal b;y Sanderson and Peai.rs (34, p.l2) and bT 22

Krogh (lJ, pp. l6J...l77) that throughout the median range, a tempera...

ture increase of one degree always produces the same acceleration in

rate of development . Within limits, the development time- temperature curve is a hyperbola, and its reciprocal is a straight line. The

· rate of acceleration slows down at the upper and .lower limits of the

developmental range . Thus 1 there are three separate rates of accel• eration by temperature t oughout the range of develop nt; one slower rate just above the threshold of develo nt, a faster rate throughout the JOOdian range, and another slower rate at temperatures above this dian range.

At temperatures below 6'1' F. the data for temperature-develop­

ment tiloo of the period from eclosion to adult for the ot-m orchard

mite fit a straight line reciprocal relationship rather closely (Figure IV). Within a temperature range of SSO to 6$° F. (and perhaps

even lower) temperature seems to be the chief factor in det rmining rate of development.

The work of Sanderson and F~airs and of Krogh, was done in the laboratory under constant temperature conditions and controlled environments . Within the natural enVironment o an organism, one

would expect other factors of the enviroruoont, in addition to

temperature, to irii'luence the rate of devolop t . This seems to

be illustrated by part of the temperature evelop . ·t time data reported here for the brown orchard mite.

The rate of acceleration of development seems to change at temperatures above 6SO F. The slope of a line fitted to the -- - -~~

23 reciprocal data above this temperature iB f l atter than a line fitted to the data at lower temperatures (Figure IV) . This indicates that at mean temperatures above 6'}J F., temperatures could be occurring during the warmer parts of the day which are beycind the median range of development.

The data obtained at temperatures above 6~ F. are scattered and do not fit a straight line very closely (Figu.."'EE· IV) . This scattering of the data may be the result of factors other than te perature affecting development . At 6.,0 F. the observed development time was 16 days, at 71° F. it was l2 da s and at 72 . ~ F. it was 15 days (Table IV) . These fluctuations above and below a dian line could indicate that at certain times certain favorable factors were effective, while at other times unfavorable !ac.tors were effec­ tive. The writer has no e.~erimental evidence to indicate what the e additional factors were . However 1 the nutritional quality of the host pl-anta and the phyeical effects of maturation of the leaves

'lDB.Y be factor of considerable ~ortance in the rate of development of this mite. In addition to the above factors the homogenei t y,_and-,.:v:at-iation_. of the data could be affected by the length of the period :between observa­ tions. At temperatures between 61' and 70° F. the development periods of the various instars ranged between three and five days . Since the observations of these individually reared mites were ade at daily intervals, there was a possible observational error of almost one day, which is l/3 to l/S of the development period. When development 24 periods were longer, the possible error was proportionally less.

If the rate of development of the brown orchard mite is slowed by temperatures associated with daily mean temperatures above 6rfl F., one can make an interesting correlation between this and the seasonal trends in populations .occurring in cherry and peach orchards. As mentioned in the section on life history and habits, unseasonally warm weather during June, 19.5.5 was associated with a decrease in the total active population of mites in orchards in 'lhe Dalles area. A slowing down or development rate at higher temperatures may be one of the reasons why the largest populations of this mite occur during the spring and fall.. This condition is just the opposite of that occurring with Tetranychus macdanieli McGregor, the other important spider mite pest of stone .fruit trees in the are , which builds up to peak popu­ lations during July and August.

The three immature stages of the brown orchard mite showed siul.ilar developmental responses to temperature. No one stage was more responsive or less responsive than the others. The data also show the lengths of the various stages to be al.Joost the same at the same mean developmental temperatures. The length or the larval st e varied from 28 . 3 days at a an development temperature of 49 .,-o F. to three days at 76 . 2° F. The 28 . 3 day development period was observed during April and early ay of 19.55. During that period temperatures in The Dalles area were considerably below normal. x.ngtb o£ Generetions 1n the Insectary

U!lde:r condit1ons o£ indiv.l.clual rearing tesw iri the insectary, the langth ot a generation of the brown orchard mite ranged trom 21 to 63 d.ap. 1he length of a generation vas oalculated by including

!ncubat.ion periods ranging from eight to 17 days, combined dewlop­ mental periodB of the three 1mm&tu:£"e inatara rangi.Dg :from U to 41 daya me preovipoaition periods ranging !rom two to .fiw days. At mean ~ratures betwec lJJO F. and 7fP r., which normally occur cl~ing Mq1 June &nd July in ~ Dalles area~ the lAngth of genera­ tiona range 1'rom 28 to 40 dq• in tbe insectary.

LIFE HISTORY AND ITS

'!his section presents the life h1story and babite of the brown orchard .rd.te 1n truit orcharda of 1be Dalles area. We histo17 etudiea of other workers are compared and ciiacuseed 1n relation to tbe findings of the vriter.

1be life cycle of the brolln orchard. mite includes an egg, a bexapocl larva1 a proton1Jiph, a deuton1Jtpb1 and m adult. Each immature stage includes a quiescent period which is terminated b7

JIIOulting. The l.i!e c;ycle differs from that of most other Tetzany­ chid mit.s in that thio species iS entire~ parthenogenet1cJ males have nnar been reported. Anderson and !brgan (l, p.4) prefer to conaicler the quiescent periods as separate stages. They report that the mitu pass through four active and three resting stages as tollowat larva, protocbrysalis, protonympb, deutoohryaal.1a1 deu~. 26 telochrysalis, and adult.

OVerwintering

Reports in the literature (1, p.l7; 7, p.l40; 8, p.l881 10, p,456; 35, p.96 and 36, p.643) and observations by the writer indicate that the brown orchard mite, Br;yobia arborea Morgan and

Anderson, overwinters in the egg stage, at least within the temper­ ate areas of its distribution. The overwintering eggs are deposited in the crevices of the bark of twigs, small branches, and fruit spurs. They are commonly laid in and aroong the exuviae of the developing summer generations and when the populations are large, the accumulation of cast skins, the deposited eggs, and the dust and debris collecting in these rough areas often give the infested limbs a gray or whit1sh cast on the under side and in areas with rough bark. During the f&ll and winter the cast skins and debris are weathered away leaving the eggs exposed. By spring they appear as bright red masses and when ~ of these masses are present they give the underside and sheltered areas of the bark a !right reddish cast.

On the other hand the clover mite; Brzybia praetiosa Koch, overwinters in all the active stages as well as the egg stage. These mites are often found in the vegetation and debr1s around orchard trees and many overwinter in the rough bark of the trunks and large scatfolding branches. These should not be confused with the brown orchard mite which has been found only on the twigs as 27 mentioned above .

Develop1nent of the Firat Generation

lhe development of the first generation of the brown orcha;rd mite differs in a number of' ways from the development of the s'llll'lll8r generations. Part of these differences result from the mites' hatching from the overwintering eggs and from the effects of cold temperature on their development. These and other differences are discussed below.

Hatching of the overwintering esg•

In 19.55 the first overwintering eggs began hatching on April. 6 and in 1956 hatching began on April 2. lhis hatching of winter eggs continues until about May l, with the peak occurring about one week alter the first hatch (Figure V) . Hatching then drops off rapidJ.3 and only a few viable eggs relnain after ten days. In 19.5.5 and 19$6 the eggs began to hatch when the green tips were just beg:inni.ng to sbov on cherry and peach trees. the peak of hatch occurred when cherry blossoms were in the be.l.loon stage and peach blossoms were beginning to open . Anderson and z.t>rgan (11 p . ll) state that in Brit.ish Columbia winter eggs begin to hatch while Mcintosh and

Delicious are in the late delayed dormant to early "mouse ear" stage of development. Other reports from Europe, Australia and the United States (lOt p. 4$6.; 19;, p . J.41 and )81 p . 8) indicate that the time of hatch of the overwintering eggs of the brown mite is 28 correlated with the beginning of growth of the host plants.

The larvae hatching from the overwintering eggs begin to feed on the tips of the opening buds when temperatures are warm enough for their activity. Within a short time they change color from scarlet or reddish orange to a dull greenish brown similar to the color of the bark on the twigs of peach_and cherry trees . They also become plump and their abdomens are 8Qillewhat extended. However., i.f the weather is cold during the egg hatching period the larvae ~ not feed for some time . They retain the scarlet color until after they have fed. This situation occurred during the egg hatching period in 1955, when average daily temperatures varied from 44° to 5SO F. between April l and. AprU 21. The newly hatched larvae gather in large masses in rough places on the bark., in the axils of the lateral buds and between the opening bud clusters. When twigs containing these masses of newly hatched larvae were placed indoors, at temperatures of 65° to 7rP F. the larvae became active in two to four hours and wandered rapidly over the stems and partially opened buds . These masses of mites on the twigs were found for 14 d.aya after hatching began.

As the larvae begin to feed, many are trapped on the sticky surfaces of the unfolding leaves or become entangled in the leaf hairs. The condition is especially prevalent on cherry trees.

On some twigs as many as 15 to 20% of the larvae present are ensnared. 29 in this manner. Examination of twigs d'Ul"i.ng the ear)¥ hatching period indicated that 10% or more of the first generation larvae are killed in this way.

After feeding, the larvae return to the rough areas on the bar:k where their dull green color blends in with their surroundinga.

1'hey remain in these areas with little activity until they are about to enter the quiescent period. They then seek a sheltered place and settle down tightly, often being partially or completely hidden in a crack or crevice. The front legs are doubled under at the genual­ tibial and tibial~tarsal joints aml tae claws are .fastened securely to the bark. The claws of the remaining legs are also attached to the bark, but the folding under is not pronounced. The mite remains 1n this position until it :moults into the next instar. 'l'he quiescent period lasts for four or five days during the spring, but is as short as one to two days during the summer.

Ecdysis

The first apparent step in ecdysis is the lateral splitting of the old cuticle on the dorsal side between the proPociosoma and the

.metopodosoma. The opening is widened 'by body movements and the dor­ sal surface of the new instar iB forced out as the two halves of the old -cuticle begin to loosen and slip away from the ends of the body.

The legs seem to be the last part to .come loose. The old cuticle may split entirely in half during the multing process and when this occurs the posterior portion often breab loose from the host plant and tne new instar fails to escape from this portion for some time. Mites with this posterior portion of the old cuticle unshed were commonly seen during the periods of the first and second moulting of the first spring generation. 'When this situation occurred with mites being individually reared, the old cuticle was lost in a short time and did not seem to impair the activities of the ndte. In normal ecdysis, however, the old cuticle remailis attached along the ventral side and the new instar emerges cleanly, leaving it attached to the host plant by the legs. These cast skins remain on the host plant for long periods of time and in areas of heavy infestations, they persist well into the winter.

In 19$$ the first multing of the larvae was observed on May 2 and the peak of larval xooulting occurred about May 6. In 19$6 the first larval moulting was observed April 10 and the peak of larval moulting occurred about April 1$ or 16.

The instar emerging at the first mult is the protonymph.

Upon completion of moulting the ny:q:>hs are again active and, if climatic conditions are suitable, they move from the twigs onto the foliage and begin feeding. Before feeding the nymphs are pale orange to tan with small olive green spots within their bodies giving them a .mottled appearance. Two distinct red spots, the eyes, stand out promi.nently on the lateral frontal corners of the dorsal surface of the propodosoma. During feeding, their bodies again 31

to to ' · 1n w cb to pe.ea the· ~ cmnt ...-.r·.... ~ . The aeti:v.e pJrO~

unl.61e to r f ·· d1nat the

qui cent s

:t.

·• t

~io~eli ·.· :r

. um \o til 1 enter t quie r i od.. Within .one os- tvo d.ap on the temperature and the development of the host plant. Some of these relationships are considered in tba previous section. 'fbe eti'ecta of te~~perature are b7 tar the greatest and are of both a

~and secondary nature. F1rat, the temperature ~recta the rate of clewlopment o£ the individual mites, both in the active and quiescent period.B. The rate of feeding is also effected by teq>era­ tun·· When "tieq)eratures are below 40° or 4f F. as they were in the

~ing of l9$S, the 111tes c:lo not feed. .Alter hatching, the 1arv84' gather in muses at tbe baaee of buds or other sheltered places during the CC!ld pttriocia. lrellf?eratun also affects the rate of development of mites, of the first generaUon aeoond&ril3 by ite effect on the boat. In some areas during the 19$$ season, many of the eggs hatched before the buds had developed. enough to allow the larvae tQ feed. fbi WMther remained cold for more than a week and. buds developed very alovq, prov1ding a very lim1tecl feeding area for the mites.

Adult

In 19$$ tbe peak 1n the adult population of the first generation o:t the ll:o1m orchard mite occurred about MQ' 241 vhi.le the corres­ ponding pea during the 19$6 season occurred about Mq 8 (Figure V).

In 19$6 t.hie peak developed about the time of pit hardening of cher%7 fruita in the area. Anderson and Morgan (1, p.1J) report that ~ peak in the ad~t population in Bt1t1sh Coluabia orcbarda ooc\DTed during tbe third week of MI.Y in 19S4J but not mtU the beg1.nn1ng or JUne o£ the 19$$ season. 3.3 Within two to !ive -·da,ys· after noulting the ad'\ll.ta begin to deposit eggs on the twigs. ,_ firat eggs were cleposited on MQ" 21. during the 1955 season, while during the 1956 seaaon the first eggs ere deposited during the first week of~. 1.be mites go through

• succession of alternate feeding and egg ~ activities through­ out the rem~Under of their life. In individual rearing exper~ts

1n the insecto17 it was foUDd that the adult mites laid t'rom one to tour eggs per clq or at one time, Often one or two days e~sed . before additional eggs were :Laid. During this period the mites were observed hiding in rough places in the cage or .feeding. The adults liv~ from one to three weeks 1n individual cages during the late spring. The 'QU1DNm D'W!lber of eggs deposited by a single mite was

31 ~ the average n'Wilber of eggs deposited was 9.6. .Anderson and

.Morgan (1, p.lJ) stated that :uPOD multing the adults feed for one

OJ" two dq8 be£ore beginning to deposit sUDJn&r eggs. They stated that each mite probab]3 lqs about .JO eggs. The aut}X)rts figure of

9.6 mJ1i¥ not be comparable w1th the est!mate of Anderson and Morgan as it represents observations 'lmder unnatural conditions of co.n.fille.., aant. Ho attempt vas made to determine the egg laying capacities of llites 1n their natural habitat. s~ Generations

n:t. peak of egg batch of the second generation 1n the orchards of !be Dalles area, as meuured by the number of new]¥ hatched larTae present on t.v1gs and. leaves occurred about JlWW 10 during the 19SS 34 seuon and abput Kay .30 during the l9S6 season. Anderoon end Morgan

(l, p.J,h) stated that the second generation begins in the latter -· half of Mq or first part of June 1n Bl'itish Columbia orchards.

Due to the extended oviposi~on period of the first generation a4ulte1 the various stages of the summer generations overlap each other. . ibis overlapping beco.-a lQOl"e pl'Qnounoed as the season pro­ greases, and maq individuals of the second and third or third1 fo\ll'th

Clci fifth generation• 'IJIIq be present on tha same twig or branch at the e&ll8 t.:I.Jae. During the 19$$ season this overlapping vas so eom. plete that no pe&ks in the population of the various stages of the di.t'!erent generations were evident. Also, during the month of June of that year lO daye of unseasonal.ly warm weather occurred. 1hie warm weather wu -sociated with a great deoreaae in the total popu-­ lation of mites and en increase in the percentage of winter eggs depositecl.

During the 19.56 aeuon, however, weather conditions were DX:Kter· ate throughout the s\JIIllDer1 and. the mite population remained much higher in the orchards of the area. Population counts made at 7-to 10-da.y intervals throughout that season seemed to shaw a progression of the generations throughout the season (as indicated 'b7 the per­ centages of the 'VU'ious stages at different times), (Figure V).

The ci&ta indicates four distinct peaka and a smaller fifth peak of adults in the population during their active season. In British Columbia (1, p.l7) there are reportecU.y four generations per year.

Miller (23 1 p.l.ll} reported that there are at least four generations .3S in Ohio and 1n some caees as lll&tly' as e1ght. other authors report three, four, or five generations per year on orchard trees (h.O, p.h.l and 16, p.302).

$UDIIQer inter Egg Deposition

There are twQ eypes of eggs laid. by the brown orchard mitet the summeJ~ egg which hatchet the s&ma seaeon it is deposited, and the vinter egg which does not batch until the spring following ita depos1tion. In the .Dalles area .most of the eggs deposited by mi.tea of the. fint generation are summer eggs and hatch vithin tw weeks1 although some are of the winter type. As the season progresses the

PfOportion of winter eggs increases. 1'be percentage of winter eggs depo8ited. by the m1tea during any one eeason of the year is intlu­ enced by weather oond.itiona and pJ"ObabJ.y by quality and av&Uabllity of the food supply. nq, hot weather during June of l9SS greatl.T reduced the populations of active brown orchard. mites 1n fruit orcharcie of t.he area and most or the eggs deposited b,- the rema:injng 1ndiv1cluaa were of the winter t.Jpe. During the 19.56 season, the build.•up of winter eggs occurred .more slowly than during the preceding year. l>i>st of the winter eggs were deposited during August and September of this aeason (Figure V). Even during September of the 19.56 season a ffN s'lliDill18r eggs were deposited and an occasional imma.ture form vas found.

1'bua 1 at least during certain years, the mitea lay .some summer eggs throughout the season.

other workers (l, p.l9 and 37 1 p.370{ report the build•up of ..

winter eggs earlier in the season. In British Columbia as many as

98% of the eggs present on the twigs during the first week 1n Jul.¥ fail. to batch until the following season. 1'his JU¥ be d\la to the

&UIIIIller eggs. being deposited on the lea-ves 1n that area. It lJiil.1 also be tb8 result or the SUIIIIIer eggs of tbe firlt generation having hatched, leaving ~ the Winter egge on the twigs. The immature I instars of the second generation dewlop during the last part of

June aud first part ot ~. Most of the aciulte ot tbe first genera­ tion die before this time, so there are few new eggs being deposited.

!he feeding habits of the brown orchard mite differ wide~ from the babita ot other p~phagous mites on fruit t.rees. Tht immature 1natars feed once or rarely twice between moults. This feeding period l&ets .f'roa a .rev hoUl"a to a whole day and is followed b7 a period of quiet hiding on the baa"k betore the quiescent period beg1n8. Both the immature f0l'JII8 and the adults retum to the bark during adwrae weather. 1'be adults were observed to feed intermitten~ throughout their egg lq1ng period. (De old concept was that these mites fed onl¥ during the night, or m&1nly at night (27, p.-12). 1he opposite of this was foun