J. Study of

Stethorus punctum (Lee.) (Cole~ptera: Ooocinellidae)

and Other Predator• ot Mitea in Mani~oàa

A Thesis Submitted to the Faculty ot Graduate Studies and Researoh of VoGill University

A. Grant :Robinsom

In Partial Fultil.lllent ot the Req111rements for the Degree of Kaster ot Science Page

I. Introduction • • • • • • • • • • • • • • • • 1 II. Aoknowledgements • • • • • • • • • • • • • • 3 III. Determination of mite speoies in Manitoba •• 4

IV. Hosta and habits of ~otetranyohus medanieli (MeG.) 5 v. List of known predaters of !• medanieli •• VI. Methods of rearing predators •••••• • • '8 VII. Stethorus punetum (Leo.) •••••••• • •

A. General r~ks • • • • • • • • • • • • • • ' B. Adult • • • • • • • • • • • • • • • • • • • 12' 1. Description • • • • • • • • • • • • • • • 12 2. Habits • • • • • • • • • • • • • • • • • 13 a. Hibernation • • • • • • • • • • • • • • 13 'b • Fllght • • • • • • • • • • • • • • • • 1.5 o. Copulation • • • • • • • • • • • • •• 15

3· Seasonal history • • • • • • • • • • • • ~ 4. Oviposi ti on records • • • • • · • • • • • 19 5. Fertility •••••••••••••••• 21

o. Egg • • • • • • • • • • • • • • • • • • • • 23

~. Description • • • • • • • • • • • • • • • 23 2. Place of deposition • • • • • • • • • • • 23 3· Developm.ent • • • • • • • • • • • • • • • 2' iii Page 4.. "Etf'eot of extreme high and 1ow temperatures on incubation • • • • • • • • • • • • • 2; ; • Time (for develop11utnt) x temperature (for

development) • • • • • • • • • • • • • 27 D. Larva • • • • • • • • • • • • • • • • • • • 37 1.. Description • • • • • • • • • • • • • • • 37 2. Habits • • • • • • • • • • • • • • • • • 38 3· Cannibalimm • • • • • • • • • • • • • • • 42 .4. Natural anemias • • • • •• • • • • • • • 42 ; • Dura ti•n ot larval ins tara • • • • • • • 43 "E. Pu})8. • • • • • • • • • • • • • • • • • • • 48 1. Formation and deseription • • • • • • • • 48 2. Duration of pupal stage • • • • • • • • 49

F. Toxioity ot DDT and methoxychlor to adu~ts of Stethorus punotua • • • • • • • • • • • • G. Taxonemie oompariaon ot s••thorua punctum wi th S'athorua pioip•a an4 St•thorus punotillum VIII. Other Coleoptara • • • • • • • • • • • • • • rx. Hemiptera • • • • • • • • • • • • • • • • • x. Thysanopt•r• • • • • • • • • • • • • • • • • XI. Diptera • • • • • • • • • • • • • • • • • • iv Page

XII. N!·europtera • • • • • • • • • • • • • • • • • 70 nn. Araehnida • • • • • • • • • • • • • • • • • 12 XIV. Iaportance of pre4atera in natural oontrol • 74

n. S'ummary • • • • • • • • • • • • • • • • • • 76 nr. Bibliography • • • • • • • • • • • • • • • • 81 LIST OJ' FIGURE Page

~ig. 1. Reproduction., in :part, of Pla te 1 trem Weldon (1909) ahowing the egg, larTa, pupa,

and adult ot Stethorus punetua. (~oh

enle.rged 30x.) • • • • • • • • • • • • ll P1g. 2. Adult of Stethorus punctum on the underside

of a leat. (~larged about 30x.) • • • 14 - 7ig. 3· ~g of Stethorus punetum on the underside of

a leat. (~rged about 90x.) • • • • 24 n.g. 4. "Zquilateral hyper'bola ahown in studiea on time (for development) x teaperature (tor develep-

ment) of eggs of Stethorus punotU.. • • 34 ng. ;. Le.st instar larva ot Stethorua punotum.

(~arged about 2;x.) • • • • • • • • • 39 Fig. 6. The tour larval instara of Stethêrua punotua.

• • • • • • • • • 40 Fig. 7• Pupa of Stèthorus punetum on the underside or

a leat. (~arga4 about 30x.} • • • • Jlig. 1. "Eapty pupal akin after emergence ot aclult of Stethoru. punotua. (Enlarged about 3Qx.) 51 Fig. ,. Ceeidemyiid maggot and host mites on the undar-

side of a lear. • • • • • • • • • • • • vi Page J1g. 10. Old ooooon and aœpty pupal Bkin of a Oecid- omyiid predaoious on mites. • • • • • • • '8 Yig. 11. Adult fly of Cecidomyiii maggot preda•ioua

on mitee. • • • • • • • • • • • • • • • ,, I. INTRODUCTION

Since the advent of DDT and other new organie insecticides, phytophagous mites, particularly those of the family Tetranychidae, have occupied increasing atten­ tion from economie entomologiste. When these insecticides were applied, as controls for certain insect pests, it was found that in almost every case populations of mites increased to suoh an extent that further ohemicals were required to control the mi tes. Theories were early ad­ vanced, and later substantiated, that the newer insect­ icides, partieularly DDT, were har.mful to predators of mites. Mites inoreased to tramendous populations when released from the control previouely exercieed by their predators. It, therefore, beeame imperative tor economie entomologiste not only to find newer and better aoaricides, but also to determine through biological etudies what arthropods are predacious on plant-feeding mites.

This study belongs to the lat~er category. It was initiated in 19.50 with a threefold objective: to determine what epecies of Tetranyohid mites are of acon-. omic importance in Manitoba; what predators are present for natural control; and what relative value eaoh predator bas as a natural control factor. The information contained 2.

herein was acoumulated during the years 1950 and 1951. Prior to this ttme no work had been dona on predators of mites in Manitoba. In two years the important mite speoies and their principal predators have been identified. MUoh more time would be needed to evaluate the importance of the role played by eaoh predator. A review of the literature on predators of mites reveals very little detailed information conoerning their biology. In general, the same forms are predaoious on all speoies of Tetranyohidae. The same speoies of predator might occur over a wide continental area, although feeding in eaoh looality on a different species of Tetranychid mite. This faot-makes a recent synopsis of the world literature on predators of the "fruit tree red spider mite", by Groves (1951), an almost complete biblio­ graphy on predators of other olosely related mite speoies. Biological studies or mite predators are being oonduoted at present elsewhere in canada and the u.s.A., but little has been published. Soma older papers whioh are worthy of mention are those by ~ng (1914), Garman (1923),

Garman and Townsend (1938), Gilliatt (1935), Lord (~949, 1949&), MoGregor and McDonough (1917), Newcomer and Yothers (1929), and Quay1e (1912, 1912a, 1932). The major portion of this study is devoted ,to the small lady beetle, Stethorus punctum, because it is considered to be the most important predator of mites in Manitoba.

II. ACKNOWL~~TS

Grate~ul aeknawledgement is made to Mr. W.A. Ross, Head, Fruit Insect Investigations, Ottawa, Canada, for suggesting the projeet and providing the opportunity for its completion. Thanks are due to all members of the staff of the Field Crop Insect Laboratory and Fruit Insect Laboratory, Brandon, Manitoba, for their helpful adviee and constructive eritioism. Partioular acknowledgament is made to Mr. J.T. Robertson, who took the photographe. The

~ollowing members of the Systematic Unit, Ottawa, assisted in the determination of species: W.J. Brown, B.P. Beirne,

~. Munroe, J.F. McAlpine, J.R. Vookeroth. The Aearina were determined by H.H.J. Nesbitt, of carleton Collage, Ottawa. The Thysanoptera ware determined by Miss Kellie O'Neill, Bureau of Entomology and Plant Quarantine, Washington, D.c. 4.

III • DJfi'ERMINATION OF MITE SPECIES IN MANITOBA

All mites studied in this project are members ot the family Tetranychidae. At present they are the only phytophagous mites which are of economie importance in Manitoba, with the possible exception of certain Eriophyidae, and the cyclamen mi te, Tarsonemus pallidus Banks. The clover mite, Bryobia praetiosa Koch, is present in Manitoba, but attraots attention only when it invades dwellings.

In 1949 1 nr. H.H.J. Nesbitt of Carleton Collage, Ottawa, identified specimens from two samples of mites from Morden, Man. as Eotetranychus paciticus (McG.) (• Tetranychus paeificus McG.). In 1950, specimens from all samples sent in from Brandon and vicinity were identified by nr. Nesbitt as ~otetranychus modanieli (McG.) (• Tetranyohus modanieli McG.). In 1951, samples from both Brandon and Morden were submitted to nr. Nesbitt. E. paoificus was identitied from a sample or mites from apple trees, Morden. ~· modamdeli was determined from black currant, Morden, plum, Morden, and rose, Brandon. On the basis of collection data it is believed that ~. modanieli is the predominant Tetranychid mite in southern Manitoba. 5·

IV • HOSTS AND HABITS OF EOTETRANYCHUS McDANIELI (McG.)

These mites attack a wide variety of trees, shrubs, and flowers in Manitoba. They have been noted feeding on apple, plum, elm, honeysuckle, mountain ash, rose, rasp­ berry, black currant, red and white currant, gooseberry, wild rose, wild bl~ck currant, spirea, caragana, hazel, sandcherry-plum hybrid, columbine, phlox, hollyhock, straw­ berry, and bean. Many more plants could probably be added to this list. Overwintering adult females emerge in the spring at the same time as the leaves appear on the host plants.

OViposition commences immadiat~ly. N.o males were sean at this time either in the spring of 1950 or 1951. Adult famales and eggs were present on raspberry on May 9 in 1951, when first observations were made. The first eggs were slow in hatching, due probably to low spring temperat­ ures, and rirst nymphs did not appear until May 2,. The number of ·generations par year is not known. Observations indioate that there are probably four.. or five, depending on temperature and general weather conditions. During sus­ tained periods of hot dry weather the mites may increase to tremendous populations. Mites were still present in very reduoed numbers when the leaves fell from treas and shrubs during the week September 23-29, 1951. 6.

Soon after the first mite eggs hatoh in the spring, mites may be found in all stages. Feeding is almost entirely from the underside of the foliage. Webbing is formed over the undersurfaoe, and the extent of the webb­ ing depends on the number of mites present. UnfavorabLe weather conditions, and predators, nor.mally prevent mites from causing economie damage. However, small tamporary outbreaks may oocur, or populations may build up during a long hot dry spell, or in plantings where insecticides whioh are harmtul to the predators have been used. If tree fruits or small fruits were grawn on a large scala in Manitoba, ·E. modanieli would probably assume far greater economie status than it does at present.

V. LI m' OF KNOWN PREDATORS OF "E. YoDA.NIELI

The fol~owing list inoludes all the known pred­ ators of -~. modanieli whioh have been determined ror Manitoba during 1950 and 1951.

Coleoptera Stethorus punotum (Lao.) Adalia bipunotata (L.) Stilbus probatus Csy. Hsmiptera Orius insidiosus (Say) Anthoooris musoulus (Say) Diaphnidia pelluoida Uhl. Hyaliodes harti Khight Hyaliodes vitripennis (Say) Plagiognathua obsourus (Uhl.) Nabis terus (L.)

Tbysanoptera Hap1othrips taurei Hd. Scolothrips sexmaculatus (Perg.) Aelothrips melaleucus Ha1.

Diptera Mfcodiplosis n.sp.? Toxomerus geminatus {Say)

Neuroptera The rollowing rive species are collection records only, from mite-infested currants. They are all suspected of feeding on mites. Soma undetermined larvae were fed on mites for considerable periode, but were not suocessfully reared. a.

Chrysopa plorabunda Fitch var. californica Coq. Chrysopa harrisii Fitch var. externa Hag. Chrysopa chi Fitch Hamerobius simulans Wlk. Hemerobius stismaterus Fitch

.A.raobnida Typhlodromus sp. (Iphidulus subgen.) Typhlodromus longipilus Nes. Anystis agilis Banks

VI. METHOOO OF REARING PREDATORS

Basically, all methode of rearing predators were the same, in that the predators were kept in closed containers, and were provided with fresh mite-intested leaves daily. Small glass vials, stoppered with cork, proved unsatisfactory due to extrema condensation in the vials. Small petri dishes, with lids, ware also unsatisfactory because the predators escaped too frequently in spite of the fact that the plates were rimmed with vaseline. Small glass shell vials stoppered with moistened absorbent cotton proved to be good rearing containers. my experience, it was found important to maintain daily the correct degree of moistness in the cotton wad, since a lack or an excess provided an unsatisfaotory habitat for both mites and predators. A lack of moisture resulted in drying of the leaves. Any condensation in the vials was detrimental to the predators, and caused a high mortality by drowning. A final compromise was reached whereby vials and cotton were ohanged avery few days, and the cotton stopper was moistened daily to a degree suffioient to prevent either dryness or an excess of moisture. This was the method used during the latter part of 1950 and all of 1951, with reasonably good resulta. rn 1950 the rearing was carried out at room temperatures. In 1951 rearing was done. in oontrolled temp­ erature cabinets, at constant temperatures.

vrr. STETHORUS PUNCTUM (LOO.)

A. GlmDAL REMARKS

This small lady beetle has been mentioned rather frequently in articles on economie entomology as being an important predator of Tetranychid mites. In the bibliography co.mpiled by Groves (1951}, s. punctum is referred to in ~o.

~7 articles. It was first named by Le Conta (1852) as Scymnus punctum, but was aventually transferred to the ganus Stethorus by Weise in 1891. After that date refer­ ences to this predator were made under either name until quite recently, when the use of Stethorus is mora commonly accepted. Very little has bean published on its life history or general biology. The first knawn work on the biology of s. punctum is that by Duffey (1891) who dascribed and made drawings of the larva, pupa and adult, but did not find the egg. The next known study of s. punctum is that by Welden (1909)• Weldon gave a very brief descrip- tion of the four life stages, namely, egg, larva, pupa, and adult. Fig. 1 is a reproduction from Weldon of draw­ ings of the four stages.

) -~ \ .. McGregor and ~~-J?

this predator, with two photographe of life stages. s. punctum is considered to be the most important predator of mites in Manitoba. References to its importance as a predator elsewhere are numerous, but specifie mention need only be made here of articles by McGregor (1914),

McGregor and McDonough (1917), and Hauser (1928}. 11.

Fig. 1. Reproduction, in part, of Plate 1 from Weldon (~909) showing the egg, larva, pupa, and adu1t ot Stethorus punot~ {Eaoh enlarged 30x.) Observations to data·in Manitoba would tend to

show that ~· punctum confines its feeding entirely to Tetranyohid mites. Adults and larvae are predacious on all forma of mites. No experimenta have been conducted as yet to ascertain if it will feed on apbids, but Parker (1913) and SWeetman and Smith (1942) record this lady beetle as predacious on aphids. No approved common name is in use for s. punctua. It is referred to by Essig (1938) along with two other species of Stethorus, as "the red spider destroyers".

H. ADULT

I.. DESCRIPTION

The original taxonomie description of the adult is that by Le Conte (1852). It is also described by mQatchley (1910). A recent and a most useful descrip­ tion, using characters of the genitalia to separate ~· punctum from other closely related species, is that by Brown ( 1950) • The adult is a very small, black, shining beetle. It is broadly oval, convex, with antennae and legs yellow. The elytra have the surface very finely punctate, and are covered With a sparse and fine pubes­ cence. Adults vary in length from 1.0 to 1.5 mm. Nor.mally the famale is slightly larger than the male. A reproduction of a drawing of an adult is shown in Fig. 1. Fig. 2 is a photograph of the adult lady beetle in its normal habitat on the underside of a leaf infested with mites

2. HABITS a. Hi berna ti on

s. punctum passes the winter in the adult for.m, hibernating in trash oover under trees or shrubs, under bark, or in other protected habitats. Although no data are available to show percentage survival, it appears that there must be a high overwintering mortality, because although adulte are plentiful in late autumn they are very scarce the following spring. In 1951 the first adults appeared on foliage infested with mites as early as May 21, but a careful search during May and June, in one planting, revealed only 10 adulte. These were brought in to the laboratory, and nine of the 10 produoed eggs, indicating that they were famales. The sax of the ramain- Fig. 2. Adult of Stethorus punotum on the underside of a leat. {1ri1arged about 3ox.) ing one was not determined. This might indicate that most of the overwintering adults are females.

b. Flight

Adults are capable of a quick jerky flight, and can fly at least a faw yards. They have been ob­ served, in the laboratory, to fly from a desk to a nearby windowwithout pausing to rest. When disturbed on a leaf in the field they may drop to the ground and feign death. Nothing is known of the distances travelled in search of prey, but it is a known fact that ~· Eunctum is almost continental in distribution in North America. c. Copulation

Copulation has been observed on many occasions both in the field and in the laboratory. Adults in co~ula assume the position normal to other beatles. Time required for copulation varies from a few seconds to two or three hours. When a mating pair is kept in one container they may mate on severa! different occas­ ions. Males will often attampt tomate with other males. 1.6.

'• SEASONAL HISTORY

It has previously been assumed in the known etv--~ literature that s. punctum bas only one generation per year. Caretul observations, and rearing, in 1950 and 1951 have shown that there are at least two generations per year in Manitoba. In the laboratory this can be increased to three, or possibly four, generations per year under favorable conditions. In 1951 the first eggs of s. punctum, in the field, were round on May 2;. The first larva, in the field, was found June 11, and the first pupa July 4. First generation adults were present after July 7, and produced the second generation. Due to the long life of soma of the overwintering females, it might be possible for overwintering, tirst, and second generation adults to be present on the leaves at the same time. In 1950 two complete generations were produced in the laboratory at room temperatures (varying from 50-80°F) • In 1951, in the laboratory, a continuous cul­ ture was maintained from May 21 to September 22, with recorded observations on the progeny derived generation by generation from overwintering females gathered May 21. All rearing was done in cotton-stoppered vials at 8ooF. Data obtained are recorded in Table r.

Table I Laboratory-reared generations of S. punctum, at 80oF

Life st e Date first recorded 1 lst generation egg May 22 lst generation larva May 26 lst generation pupa June 3

lst generation adu~t June 6 2nd generation egg JlUle 18 2nd generation larva June 26 2nd generation pupa July 13 2nd generation adu1t July 16 3rd generation egg July 26 3rd generation larva August .5 }rd generation pupa August 18 3rd generation adult August 21 4th eneration e Se tember 6

In the laboratory, at a constant temperature of 80oF, three complete generations were produced. With l.8.

improved techniques and better segregation of mating pairs, there appears to be no reason why four complete generations could not be reared, in the laboratory, in one year under favorable conditions. Nine third generation adults were available by August 25. These were separated into two vials, of four and five respectively, with sex undetermined. On the completion of the project on Septem­ ber 22, the nine adults were determined, by dissection, to be females. This would explain why no fertile eggs for a fourth generation of beatles were produced. It is interesting to note that a complete gener­ ation can be reared in the early spring, in the laboratory, b·efore the first larvae can be found in the field. Adult beatles were present on leaves, feeding on mites, in 1951 until September 22, when a heavy frost occurred. Approximately 2000 leaves were examined from

September ~ to 22, but during this period only one egg of s. punotum was found. The number of eggs in the field, noted during August, gradually declined after August 15.

During the period August 15-3~ larvae and pupae were still plentiful. A few larvae and pupae could be found during September. This would indicate that oviposition declines after August 15 and practioally ceases in the field after Septamber 1. In the laboratory, there was no cessation of oviposition by females of s. punotum kept at a constant temperature of 80°F, as long as mites were available. No information was obtained regarding the statua of beatles entering hibernation. Adults from both the first and second generations may go into hibernation. In this connection it is interesting to note that Putman (1951), working with the olosely related speoies s. punctillum, has shown that overwintering adults had entered hibernation for a second winter. If they sucoessfully overwinter for a second winter, it is possible that certain adults of

~· punotum may do the same. In the laboratory, adults maturing as lata as August 15 will still produce eggs in the same year. In the field it is unlikely that adults maturing at so lata a date would oviposit betore entering hibernation.

4. OVIPOSITION RECORDS

Daily records were kept of the number of eggs laid per individual by sevan overwintering females, beginning with the first date for oviposition after collection from the field, until the death of the female. The reason for each death is unknown 1 but in soma cases it may have 20.

been due to faulty handling techniques.. The data for sevan overwintering females are shown in Table II.

Table II Oviposition records for sevan overwintering females of s. punctum, 19.51

Total Beetle Recorded dates No. of No. of Average per famale per day No. _F'rom To da ys eggs (closest whole numberl 1 May 21 July 12 52 1.54 3 2 May 21 August 1 72 292 4 3 May 22 June 13 22 2.5 1. 4 May 23 June 20 28 12 1 .5 May 23 June 8 16 2.5 2 6 May 24 June 9 16 11 1 7 June 1.5 July 3_0 4.5 244 5

Similar records were kept for eight first generation females. The data are shown in Table III· 21.

Table III Oviposition records for aight first generation fema1es of ~· punctum, 1951

Total Beetle Recorded datas No. of No. of Average per female per day No. From To da ys 8;(;(S {closest whole number) 1 July 24 August 1 8 77 10 2 July 25 August 2 8 30 4 . . 3 August 6 Sept. 2~ 46 15.5 3 4 August 6 August 23 17 59 3 5 August 6 Sept. 21 46 214 5 6 August 7 August 29 22 58 3 7 August 7 August 14 7 22 3 8 August 7 Sept. 21 45 266 6

The greatest number of eggs laid by any one female, in a 24-hour period, was 24 •

.5 • FERTILITY

Observations indicate that mating is necessary for the production of fertile eggs. Female beatles, whioh have never mated, will often lay infertile eggs. One unmated female laid 71 infertile eggs in nina days. Al1 the eggs collapsed within two days, and there was apparently no embryological development. Ocoasionally, the first 22 ..

rew eggs from a mated female are infertile. The sevan overwintering females (Table II) were isolated when captured in the spring. No copulation occurred after their capture and isolation. All produced fertile eggs until they died. One of these females laid 292 fertile eggs between May 21 and August 1, 1951. It is possible that fertilization of overwinter­ ing females takes place the previous year, with no further copulation neoessary. Sevan first generation adults were segregated as mating pairs as soon as they were observed mating in the laboratory. Table IV shows the time interval between mating and production of fertile eggs.

Table IV Time interval between mating and oviposition for sevan first generation adults of s. punctum, 1951

Beetl.e No. of No. Date observed ma ting Date :rirst eggs produoed days 1 July 1.9 July 24 5 2 July 20 July 25 5 3 August lL August 6 5 4 August 1 August 6 .5 .5 August 2 August 6 4 6 August 2 August 7 .5

7 ,A.lJg__US t 3 Augl!st 7 4 c. ]Qg

1. DESCRIPTION

The egg 1s about 0.3 mn. long, 0.15 mm. wide, and oval in shape. It is pearly white when laid. The chorion has a pronounced sculpturing. Fig. 1 shows a smalL reprint of a drawing of an egg, and Fig. 3 is a photograph of an egg of §• punctum.

2. PLAC~ OF DEPOSITION

The eggs are deposited on the underside of leaves infested with mites. When found in the field there is nor­ mally one egg to a laar, but if the mite population on a leaf is large, there may be two or three. They are laid singly, although occasionally two or three may be found close together in one small area. They are usually round close to a leaf vein, often underneath the webbing made from vein to vain by the mites, and sometimes even partly hidden

under mite exuviae or miscellaneous deb~is on the laar. The eggs adhere tightly to the undersurface of the leaf, as though the egg chorion had been sticky when laid, and had hardened immediately. In laboratory rearing, only one leaf was available to the female during each 24-hour period. As 24.

Fig. ;. ~g of Stethorus aunotum on the underside of a leaf. {lïîlârge about 90x.) 2.5.

a result 4 to 10: eggs per leaf were common. On one occasion 24 eggs were .found on one plum leaf after the 24-hour period.

3 • DEVELOPMENT

No embryological studies were made during the project. The egg remains pearly white for about half the incubation period, and then very gradually begins to darken. About this time two small pink eye-spots appear on one end of the egg. About 36 hours before the larve is due to emerge, the whole egg turns greyish-hlack. The chorion splits lengthwise down both aides, from one end, to a distance of about one-half the total length, and the larve emerges head first.

4. EFFECT OF EXTREME HIGH .AND LOW TEMPERATURES ON INCUBATION

Eggs of s. punctum were kept at constant temper­ atures of 4oo, 50o, 5.50·, and llODF to determine the effeot of extrema high and low temperatures on incubation. Resulta are shown in Table v. 26.

Table V Incubation tests of eggs of s. punctum at miscellaneous high and low temperatures, 19.51

No. of days No. of Temperature No. of days at 8oo No. of eggs e~~s for test of test after test hatching_ 76 40°F 12 4 12 22 .50°F 12 3 8 :;6 .5.5oF 2.5 none 0 56 ll0°F 4 none 0

At .5.5°F, after 2.5 days the eggs were no longer viable, because of deterioration. At 11oo, after 4 days the eggs were desiccated. The temperature range for incubation of eggs of s. punctum apparently lies somewhere between .5.5°-ll0°F. Table V shows that eggs of s. punctum can with­ stand low temperatures of 40° or ;o°F for a few days, and soma will still produce larvae when subjected to more favorable temperatures. Howevar, prolonged axposure to cold, aven at .5.5~, will eventually destroy the ambryo. 27 •

.5• TIME (FOR DlWELOPMENT) x TEMPERATURE (FOR DEVELOPMENT)

In 19.51, various constant temperatures from 5.5°- 1100F were used in a study of the relation of temperature to development of the egg. No equipment was available to main­ tain a constant humidity, but a suitable humidity was main­ tained by moistening daily the cotton plugs in the necks of the vials. Results obtained at a constant temperature of 60°F are shown in Table VI.

Table VI Time for development of eggs of s. punctum at 60°F

No. of e s No. of da s for incubation 1 10 6 ll 14 12 7 13 11 14 2 1.5 1.0 16 5 1 No. of eggs not hatching 21 Total no. of eggs 77 Average no. of days for incubation 1}.6 28.

Resu1ts obtained at a constant temperature of 65°F are shawn in Table VII.

Table VII Time for development of eggs of s. punctum at 65°F

No. of eggs No. of days for incubation 2 7 6 8 6 9 14 10 18 11 2 12

No. of eggs not hatching ~9 Total no. of eggs 67 Average no. of days for incubation 9•9

Results obtained at a constant temperature of ?0°F are shawn in Table VIII. Table VIII

Time for development of eggs of s. punctum at ?0°F

No. of e s No. of da s for incubation 8 6 28 7 2.5 8 .5 No. of eggs not hatching 1.5 Total no. of eggs 81 Average no. of days for incubation ?.4-

Results obtained at a constant temperature of ?.5°F are shown in Table IX. 30.

Table IX Time for development of eggs of s. punctum at 7.5°F

No. of e_ggs No. of da_ys for incubation 8 3 29 4.

~7 .5 3 6 No. of eggs not hatehing 2 Total no. of eggs .59 Average no. of days for incubation 4.3

Resulta obtained at a constant temperature of 80°F are shawn in Table x.

Tabl.e X Time for dewelopment of eggs of s. punctum at 80°F

No. of eggs No. of days for incubation 3 3 46 4 3 .5 3 6 No. of eggs not hatohing 0 Total no. of eggs .5.5 Average no. of days for incubation 4.1 31.

Resulta obtained at a constant temperature of 90°F are shown in Table ll.

Table XI Time for development of eggs of s. punctum at 90°F

No. of e 8 No. of da s for incubation 3.5 3 20 4 2

No. of eggs not hatohing ~ Total no. of eggs .58 Average no. of days for incubation 3·4

Results obtained at a constant temperature of l00°F are shown in Table XII.

Table XII Time for development of eggs of s. punotum at l00°F

No. of eggs No. of days for incubation 2

~o. of eggs not hatching 3 Total no. of eggs .55 Average no. of days for incubation 3 32.

Resulta for all temperatures are summarized in Table XIII.

Table XIII

Summary of time x temperature studies on eggs of s. punctum

Per cent Average no. Temperature No. of eggs of eggs of days used not hatchi.np; for incubation 110°F 56 l.OO -- 100° 5.5: .5·.5 3 90° .58 1.7 3.4 80° .5.5 0 4.1 7.50 .59 3·4 4.3 70° 81 18.,5 7·4 6.50 67 28.4 9·9 6o0 77 27·3 13.6

.5.50 36 ~00 --

It is apparent from a study of Table XIII that embryological development is progressively delayed by lower temperatures. When the data are plotted, as in Fig. 4, the co-ordinates conform closely to the characteristic hyperbola 33·

round in most studies on the relation of temperature to development.

There was no mortality at 80~, which might be considered as the optimum temperature. Table XIII shows that there is a tendency for higher mortality in the egg as rearing temperatures inorease or decrease from the op- timum. The optimum is oloser to the maximum than to the minimum. Another tendenoy was observed from this study. At l00°F the eggs hatched on one day. At 60°F the eggs hatohed on eight different days. There is soma evidence that the number of days on which larvae emerge is prolonged at lower temperatures •. The evidence for this may be found in Taltüe XIV.

Table XIV Erfeot of temperature on hatching or eggs of s. punctum

Range in days on No. of days on TemPera ture which eggs hatohed which eP';gS hatehed 100°F 3rd 1 90° 3rd to 5th 3 80° 3rd to 6th 4 75° 3rd to 6th 4 70° 6th to 9th 4 65° ?th to 12th 6 6o0 l.Oth to 17th a fig. 4. Equilateral hrperbola shown in stu41.•• on tillle (tor developm•nt) x tea.Per._t~• (tor d•v•lepment) on eg~s ot Stethoraa punotua.

3.5·

In addition to the incubation data recorded in Tables VI to XIII, a record was kept of the incubation period of miscellaneous groups of eggs at various times during the project. There was a total of 173 eggs, and all were held at 80°F. This information is shown in Table xv.

Table X.V Time for development of eggs of s. punctum at 800F (miscellaneous data)

No. of e s No. of da s for incubation. 45

12~ 4 7

Total no. of eggs ~73 Average no. of days for incubation 3.8

No data are available for the time required for development at normal fluctuating temperatures in the field or in an insectary. In 1950, some data were record­ ad for incubation at normal fluctuating room temperatures varying from 50-80°F. During the pariod June 7 to 23, the incubation period of 10 eggs laid in the laboratory ------·--·- -··· ;6.

was determined. The data are recorded in Table XVI.

Table XVI Time for development of eggs of s. Iunctum at room temperatures, June 7-21, 950

No. of e s No. of da s for incubation 3 6 2 7 8 Total no. of eggs 10 Average no. of days for incubation 7.2

The incubation period of a second group of eggs, held at room temperatures during the period August 5 to 14, 1950, was also recorded. The data are shown in Table XVII. 37·

Table XVII Time for development of eggs of s. punctum at room temperatures, August 5-T4, 1950

No. of e s No. of da s for incubation

6 4 6 Total no. of eggs 12 Average no. of days for incubation 4.5

D. LARVA

1. DESCRIPTION

There are four instars in the larval development. The larvae are ash gray to brown. Colour may vary slightly between instars, and also within each instar, depending on whether the larva has reoently shed, or is soon to shed an exuviae. Eaoh segment of the thorax has a pair of

irregular brown spots on the dorsal surface. ~ach of the nina segments of the abdomen, except the last, has six whorls of bristles dorsally. A taxonomie description of the larva of s. punotum is given by Paterson (1951). 38.

Measurements were made only of last instar larvae. They vary in length from 1.5 to 2.5 mm. It is difficult to state an exact measurement for a last instar larva, because it grows shorter and thicker as it approaches pupation. A reprint of a drawing of a larva of s. punctum is shown in Fig. 1. Fig. 5 is a photograph of a last instar larva which is nearing pupation. Fig. 6 shows the four larval instars of s. punctum.

2. HABITS

Stethorus picipes is so closely related to s. punctum that it may possibly be a subspecies or geographical race of the latter. The male genitalia are identical, and the only taxonomie difference seems to be that of colour of mouth parts and legs, which in s. punctum are partly yellow, and in s. picipes entirely brownish or black. It would seem reasonable to assume that the somewhat datailed observations of Newcomer and Yothers (1929) and Fleschner (1950) on larvae of s. picipes would be applicable to larvae of s. punctum. Newcomar and Yothers give data on numbers of mites and mite eggs consumed. Their description of the peculiar feeding habit of larvae of s. picipes has been noted in larvae of s. punctum, in which the fluid contents of a mitets body are alternately drained by the larvae and Fig. s. Last instar larva o~ Stethorus punotua (~rged about 2;x.) 40.

Fig. 6. The tour larval instars ot Stethorus punotum. ("'Knl.arged about 2;x.) ------···· 41.

regurgitated back into the body of the host, this process being repeated severa! times before completion of the feeding process. These authors state, "The purpose of this pumping back and forth seems to be to rinse out thor­ oughly all available food from the host's body.n Some interesting data are given by Fleschner on the searching capacity of larvae of s. picipes, and figures

are given for area of perception, sp~ed t:r:~Y:E:l.l~ed while search­ ing, and total area searched in one hour, with further data on number of mites consumed and time required to consume one mite. Observations made on s. punctum support the statament made by Fleschner that the larvae of s. picipes do not perceive the presence of the prey until actuel phys­ ical contact has been made. Another statement which is also worthy of note is that "Stethorus larvae can consume a far greater quantity of food than is actually necessary for them to complete their larval development, and that the more they consume daily, the more quickly they complete their larval development.n

Occasionally when larvae of ~· punctum are molested they will excrete two small droplets of fluid from glands apparently located on the dorsal side of the abdomen, near

the thorax. The exact location of these glands was not 42.

determined. The excretion of these droplets was particularly noti ceab,le wh en larvae were being anesthetized for photo­ graphy.

3• CANNIBALISM

Whenever several larvae were placed in one small vial in the laboratory, thair numbars would invariably be reduced to one or two individuals by cannibalism. This was more marked when the host mites offered as food were scarce, but occurred often even when food was plentiful. A larger larva would readily seize and devour a smaller one encountered during their search for mites. Under natural conditions cannibalism is probably not frequent, because there is usually only one larva on a leaf.

4. NATURAL EN»JJES

No parasitism of any stage of s. punctum was noted in the field. No predation was noted on larvaa of s. punctum in the field. In the laboratory, larvae of s. punctum are raadily attacked by nymphs and adults of Orius insidiosus, Anthocoris musculus, and other Hemipteron predators, and also by any of the Nauroptaron larvae found in the same habitat. .5. DURATION OF LARVAL INSTARS

Larvae of s. punctum were reared in small glass vials stoppered with absorbent cotton. They were trans­ ferred daily from an old leaf to a fresh leaf with mites on it for food. It was found that this transfer could best be effected by lifting the larva gently on the point of an insect mounting pin, being careful not to pierce the integ- um.ent. In a study of the duration of each instar, of larvae reared at a constant temperature of 80°F, 103 larvae were started, of which only 43 were successfully reared to pupation. Table XVIII shows the number which died in each instar, and per cent of total loss.

Table XVIII Mortality by instars during rearing of 103 larvae of s. punctum

.J:'er cent of Instar No. of larvae dying total deaths

1 40 66.7 2 9 1,5.0 3 3 ;.o 4 8 13.3 Total 60 100.0 44.

The loss of 60 larvae would indicate that there is still need for improvement in techniques. The loss of two-thirds of the 60 in the first instar would indic- ate that this is the critical period during rearing of larvae in the laboratory. This is substantiated to seme

1?\· extend by observations in the field, as dead larvae of s. punctum found on leaves are nearly always individuals in their first instar that have succumbed due to various reasons, possibly predation, cannibalism, heavy precipit­

ation, or occasionally even by becoming entangled in webbing

made by dense populations of mites. Table XIX shows the duration of each instar of the 43 larvae successfully reared to pupae. To shorten the table, larvae have been grouped together where larval histories were identical.

At 80~ the duratiorsof the first and last instars are approximately the same length of time. Similarly, the second and third instars are of equal duration. Con­ firmation of these average durations is obtained when the data from the larvae which did not complete their develop­ ment are presented in tabular for.m (Table XX). Tabla XIX Duration of larval instars of 43 larvaa of s. punctum reared to pupaa, at 80°F

No. of Duration of larval instars in days Total no. larvaa lst 2nd 3rd 4th of days 1 1 1 1 2 .5 1 1 2 1 3 7 1 1 2 2 2 7 1 1 2 2 3 8 .5 2 1 1 2 6 7 2 1 1 3 7 1 2 1 1 4 8 1 2 1 2 1 6 .5 2 1 2 2 7 1 2 1 2 3 8 1 2 2 1 2 7 4 2 2 1 3 8 3 2 2 2 2 8 1 2 2 2 3 9

~ 2 3 1 2 8 1 2 3 1 3 9 2 3 1 1 2 7 3 3 1 1 3 a 1 3 1 3 2 9 1 3 2 1 3 9 1. 3 3 1 2 9 Tota~ ~va. 2.1 Ave. 1.4 Ave. 1.4 Ave. 2 • .5 Ave. 7.4 43 da~s da ys days daye da_ys 46.

Tab~e XX Duration of larval instars of larvae of s. punctum which died in 2nd• 3rd, or 4th instars during rearing at 80°F

No. of larvae Average no. Instar 1 day 2 days 3 days of da_ys 1st 6 10 4 1.9 2nd 7 3 1 1.4 3rd .5 3 0 1.4

In 19.51, 72 larvae were reared to pupae, at 80°F, but no record was kept of the duration of each instar. The total 1ength of the larval life of these larvae is shown in Table XXI.

Table XJa Duration of larval life of 72 larvae of s. punctum, reared at 8ooF

No. of larvae No. of da s in larval sta e 4 6 11 7 18 8 17 9 14 10 4 11 3 12 1 1:; Average duration 8.7 days 47.

The average duration of 8.7 days, for the larval life of this group, is slightly greater than that of 7•4 days for the larvae shown in Table XIX. This increase might be attributed to the fact that soma of the larvae shown in Table XXI were not reared individually in vials, and were subject to competition for food. Some data are available for duration of larval instars of larvae reared at room temperatures, in 1950. Room temperatures in the laboratory varied from 50-800F. Recorded resulta are shown for eight larvae, in Table XAII.

Table XXII Duration of larval instars of eight larvae of s. punctum reared at "room temgeratures" fluctuating from 50-80 F

Date larva I.UuraliJ.on o1· .larva_b 1nstars J.n aays 'l'ota.L no. O!" emerrz.ed lst 2nd 3rd 4th da ys August 10 3 2 1 6 12 August 11 2 2 1 7 12 August 11 2 2 2 7 13

August 1~ 4 1 2 8 15 August 13 3 2 3 6 14 August 13 3 1 2 6 12 August 14 2 2 2 6 12 August 16 3 3 4 6 16 Average 2.8 1._2_ 2.1 6._5 13.3 48.

At 80°F the average duration of larval life was 7.4 days, and at "room temperatures" 13.3 days. The differ­ ence in time is found almost entirely in the last instar. It appears that duration of larval life is shortened con­ siderably by higher and constant temperatures, as opposed to lower and fluctuating room temperatures. Room temperatures would more closely approximate natural temperatures in the field, where observations indicate that larval life ranges from 12 to 30 days, depending on weather and food supply.

E. PUPA

1. FORMATION AND DESCRIPTION

The last instar larva attaches itself to the underside of a leaf by the anal end of the abdomen 24 to 48 hours prior to pupation, and remains without feeding or locomotory movement in this "prepupal11 condition. The fourth exuviae is shed, and worked down to the anal end of the abdomen, where it remains. When the exuviae has been shed, the pupa is very light brown, or yellowish. The pupa turns black in about four hours, and remains black until the adult emerges. The emerging adult is very light brown, or yellowish, but turns black in about four hours. The adult crawls out head first from under the pupal skin, leaving it attached to the leaf, as shown in Fig. 8. The pupa is flattened, in dorsal view, rounded anteriorly, and pointed posteriorly. It is covered with fine hairs. A photograph of a pupa is shown in Fig. 7•

2. DURATION OF PUPAL STAGE

A record was kept of the duration of the pupal stage, at 80~, for 101 pupae during the season of 1951. Results are shawn in Table XXIII.

Table XXIII Duration of pupal stage of s. punctum at 80°F

No. of u ae

~ 2 68 3 15 4 Average 3.0 days

In 1950, pupae were retained at room temperatures varying from ;o~0°F. Table XXIV shows the data recorded for 30 first generation pupae. Fig. 7• Pupa of Stethorus punotum on the underside of a leat. (Enlarged about 30x.) Fig. 8. ~pty pupal s~in after emergence of adult of Stethorus punotum. (~larged about ~ox.) 52-

Tabl.e XXIV Duration of pupal stage of s. punctum at room temperatures

No. of No. of days larvae Date pupated Date adul ts emerged in pupal stage 2 July 13 July 19 6

1 July 16 July 2~ 5

2 July ~? Ju1y 21 4

~ Ju1y 18 Ju1y 24 6 2 Ju1y 19 Ju1y 24 5 3 Ju1y 20 Ju1y 26 6 1 July 21 July 26 .5

1 July 22 July 26 4 3 July 22 July 27 .5 3 July 25 July 28 3

3 July 26 July 29 ~ 3 July 27 July 29 2 5 July 27_ July 30 ~ Average no. of days in pupal stage 4.0

Table XXV shows the duration of pupa1 stage at room temperatures for seven second generation pupae reared in 1950. -

Table XXV Duration of pupal stage of s. punctum at room temperatures

No. of days Date pupated Date adults emerged in pupal stage August 22 August 28 6 August 22 August 29 7 August 24 August 29 .5 August 2.5 August 30 .5 August 26 August 31 .5 August 27 August 31 4

August 28 September ~ 4 Average no. of days in pupal stage _5.1

A comparison between pupae kept at room tamper- atures, and those retained at a constant temperature of 80°F, shows that the time spent in the pupal stage is shortened by higher and constant temperatures. F. TOXICITY OF DDT AND METHOXYCHLOR TO ADULTS OF STETHORUS PUNCTUM

There has been frequent reference in published entomological literature to the harmful affect of insect­ icides on pradators of mites, and particularly their to:x::ic­ ity to the small lady beetle, Stethorus punctum. Clancy and

Pellard (~948) assess this beetle as comprising 80 per cent of the total mite predator population, and state "This coccinellid was easily killed by DDT." Steiner et al (1944) in field plot tests with different insecticides

noted that ~· punctum was absent from DDT plots but present on adjacent lead arsenate and nicotine plots. Rosenstiel (19.50) has studied the toxic affects of parathion and 88-R on bath larvae and adults. Other workers also have re- ported on the harmful affects of various insecticides to this lady beetle. Methoxychlor may replace DDT for certain uses, because of its lower mammalian toxicity, but little is known as yet of its harmful affect on predators of mites. The following experiment was designed to ascertain whether methoxychlor is harn~ul to this lady beetle in the adult stage, and to compare the possible toxicity of methoxychlor with that of DDT. The rate of DDT and methoxyohlor used in the experiment was the same as that reoommended for control of the ourrant fruit fly, namely, 1/2 lb. teohnioal per lOO gal. of water (Andison et al 1951). Suffioient DDT, as wettable powder, was added to a quart of distilled water, and plaoed in a 2-quart sealer, to give the same concentration as one postblossom spray of DDT on ourrant bushes. The same was done wi th methoxyohlor in another 2-quart sealer. A third sealer, to be used as a check, oontained 1 quart of distilled water. Leaves, either of honeysuokle or of plum, severely infested with mites, Eotetranyohus modanieli (MoG.), were out to fit into the bottom of a Syracuse watoh glass. When a treated leaf with beatles on it was placed in the Syracuse watch glass, another suoh glass was placed on top to act as a lid and prevent the beatles from esoaping. When a certain period of time had elapsed, a fresh untreated leaf was placed in the top glass, and the bottom portion then used as a lid. This ensured that after the time of treatment had elapsed, the beetles were re.moved to an unoontaminated leaf, in an uncontamin­ ated glass. 56.

To start the experiment, the sealer containing DDT was thoroughly shaken, to make an even suspension of particles throughout the quart of mixture. A leaf was immersed and held in the suspension for two minutes, then removed and allowed to dry. The same was done for methoxy­ chlor. The distilled water was not shaken, but the leaf to be used was immersed for the same length of time. When the leaves had dried, most of the mites on them were still alive, and available as food for the adult beetles. Five beetles were placed on a leaf treated with DDT, five on a leaf treated with methoxychlor, and five on a leaf from the check, of water. ~ach set of five was left in the watch glass wi th the leaf concern.ed, for one-half hour. At the end of the half hour, the beetles were removed to a fresh untreated leaf, in the other glass. A fresh untreated leaf was given to each set of five at the end of 24 hours. At the end of 48 hours a check was made to determine possible toxicity. All beatles were still alive in all three glasses. It was then decided to expose the beatles to treated leaves for two hours, instead of one-half hour. The same procedure was followed as formerly, using the same 15 beetles, and at the end of 48 hours,four were dead from the DDT and three from the methoxychlor. The two- minute immersion of the leaf and two-hour exposure was used for the remainder of the experiment, except for two final series at 24 and 48 hours. Adult beatles were obtained by collecting pupae and adulte from mite-infested leaves in the field. This meant that the beatles were not all of the same age, or even of the same generation, but probably at the time of collecting the majority of the beatles were first generation, and less than three weeks old. A total of 210 adult beetles was used, 70 for each of the treatments. The resulta are shown in Table XXVI. The adult beatles were placed directly onto the treated leaves at the beginning of the two-hour exposure, but there was nothing to prevent them from leaving the leaf and remaining on the sides of the glass, for the period. However, in most cases they went onto the leaves to feed on the mites. In all observed cases, 10 minutes on a treated leaf was sufficient to cause the beatles to become agitated, and walk with a peculiar jerky move­ ment, and eventually fall on their sidas or back. This happened with both the DDT and methoxychlor. The large number of survivors would indicate that those surviving after the exposure period were probably those that did not spend many minutes on the leaf, and were able to detoxify ,58.

Table XXVI Toxicity of DDT and methoxychlor to adults of s. punctum, 2-hour exposure

Date of ~o. dead out of ,2 1 at end of 4--s- hours exp os ure DDT Methoxychlor Check August 7 1 .5 0 August 7 4 4 0 August 9 3 2 0 August 9 1 3 0 August 10 1 2 0 August 13 4 3 0 August 13 4 .4 0 August 13 .5 4 0 August 1.5 3 2 0 August 1.5 0 3 0 August 1.5 3 0 0 August 17 1 2 0 August 17 3 4 0 August 17 0 4 0 Total dead of 70 beetles 33 42 0 59·

and recover from the poison. Recovered adults were kept from certain of the tests, and they appeared quite normal afterwards, copulating, feeding, and laying fertile eggs. One female from the first two-hour exposure to DDT, laid eight eggs within 24 hours after the test, and eventually laid 266 eggs between August 7 and September 21. Adults from some of the tests, recorded as dead, were kept, and they did not subsequently recover. To determine what might happen if the adult beatles remained with the treated leaves for periods longer than two hours, 20 adults, in groups of five, were left for the entire 48 hours in the glass with the treated leaf. The number dead was counted at the end of 24 hours, and again at the end of 48 hours. Results are shown in Table XXVII. From Table XXVI it would appear that, under the conditions of this experiment, methoxychlor is as taxie to adults of s. ~unctum as is DDT. An analysis of variance showed that, on the basis of these data, methoxychlor is not more taxie than DDT. The data in Table XXVII confirm that methoxychlor and DDr are equally toxic to adults of s. punctum. 60.

Table XXVII Toxicity of DDT and methoxychlor to adults of s. punctum, 24- and 48-hour exposures

No. dead out of 5 No. dead out of 5 No. dead out of 5 Date of DDT Methox chlor Check exp os ure 24 hours 4~ hours 24 hours 4~ hours 4e hours August 23 3 4 5 5 0 August 23 4 4 3 5 0 August 24 1 3 2 3 0 1 August 24 1 3 3 3 0 Total dead of 20 9 14 13 ~6 0 beatles

G. TAXONOMie COMPARISON OF STETHORUS PUNCTUM WITH

STETHORUS PICIPES AND STETHORUS PUNCTILLUM

In addition to s. punctum, two other closely related species of Stethorus occur in Canada. s. picipes is round in British Columbia, and s. punctillum in Southern Ontario. s. picipes can only be separated from s. punctum on the basis of color, which leads one to suppose that it may be a subspecies or a geographical race of s. punctum. s. punctillum is an introduced species, from Europe. It apparently occurs only in a small area

in the Niagara Peninsule, where it appears to have re- placed s. punctum which is known to have occurred there 20 to 30 years ago. All three species are so similar in appearance that they can not be distinguished from one another in the field. It has been suggested that there might be some consistent morphological character which has been hitherto overlooked, and which might become appar­ ent from a closer study. Adults of s. picipes were obtained from Mr. c.v.G. Morgan at Summerland, B.c., and of s. punctillum from Mr. W.L. Putman at Vineland Station, Ontario. Comparisons were made of the three species, using in particular the keys found in Brown (1950} and Kapur (~948). Brown, refarring to .§.• punctillum, states, "It is con­ fused in collections with s. punctum (Lee.) from which it is separable only by characters of the genitalia.n And in the key the same author refers to s. picipes

'~outh parts and legs entirely brown or blackish; not separable otherwise from punctum." Comparisons made between these three species failed to divulge any new information, and only served to verify the above quotat­ ions. 62.

VIII. OTHER COL~OPTERA

Adults and first instar larvae of Adalia bipunctata were occasionally found feeding on mites in the field. Larvae could not be reared on mites. Various species of aphids are the main food of this lady beetle, and the number of mites destroyed by it is very small. This is probably true of several other large lady beatles. All the Coccinellidae noted by Lord (1949a) which will feed on the European red mite, are present in Manitoba, and may be occasionally predacious on E. mcdanieli. On June 24, 1951, a larva was found on a mite­ infested leaf in the field. This one specimen was the only larva of Phalacridae found during the seasons of 1950 and 1951. It was given fresh mites daily, and was observed feeding on nymphs and adults. This larva pupated on July 6, and the adult emerged July 10. The adult has been determined by Mr. W.J. Brown as Stilbus probatus. This is the first known record for this species as a predator of mites. Larvae of Phalacridae are generally considered to be phyto­ phagous, but little is known of their habits. It may be that sorne species are sufficiently adaptable to be both predacious and phytophagous, particularly if the prey is as soft-bodied as a mite or an aphid. IX. IDMIPTERA

Orius insidiosus and Anthocoris musculus are the most important of the plant bugs predacious on mites in Manitoba. o. insidiosus outnumbers A. musculus in individuals, and both are more abundant than any of the other predacious bugs. Both were reared successfully on a diet of Tetranychid mites, in cotton-stoppered vials in the laboratory. Both are known to be cannibalistic when confined in vials. Either will attack larvae of s. punctum. Both nymphs and adulte are predacious. Under natural con­ ditions they are probably general feeders. Nabis ferus can be successfully reared on mites, in the laboratory. Individuals have also been taken, both nymphs and adults, on mite-infested leaves. No previous record has been found in the literature that N. ferus is predacious on Tetranychid mites. It is known as a beneficial insect because it preys on pests of vegetable gardens, including such forms as comparatively large caterpillars. Other plant bugs which are known to occasionally prey on mites in Manitoba are Diaphnidia pellucida, Hyaliodes harti, Hyaliodes vitripennis, and Plagiognathus obscurus. 64.

All the species mentioned above were deter­ mined by Dr. B.F. Beirne of the Systematic Unit, Ottawa.

X. THYSANOPYERA

Three species of thrips are known to be predac­ ious on mites in Manitoba. They have been determined by Miss Kellie O'Neill of the Bureau of Entomology and Plant

~uarantine, Washington, D.O., as Haplothrips faurei, Scolothrips sexmaculatus, and Aelothrips melaleucus. H. faurei is a common and important predator of mites in Manitoba. Nymphs and adults of this species were present and active during.the entire seasons of both 1950 and 1951. In the latter year one adult was noted as early as May 9· Nymphs were successfully reared to adults in cotton-stoppered vials in the laboratory. The bionom­ ics of H. faurei have been outlined in some detail by MacPhee {1-94 7) • s. sexmaculatus is also a common and important predator. It is more commonly sean from July 15 to the end of the season. During this period it is more frequently found than H. faurei. Nymphs were successfully reared to adults in cotton-stoppered vials in the laboratory. The life history and habits of this thrips are given by Bailey (1939)· No information, other than a collection record, is avai1ab1e for A. me1a1eucus. One specimen was taken feeding on mites at Morden, Man., in 1950. A short note on this species in Ontario is given by Putman (1942).

XI. DIPTERA

A species of Cecidomyiidae is predacious in the maggot form on mites in Manitoba, and is an important predator. Adu1ts submitted to the Systematic Unit at Ottawa were identified by Mr. J.F. McAlpine as "Cecidomyiidae - tribe Diplosariae - probably MyCOdiplosis sp. or possibly Acaroletes sp. - probably an undescribed species". Eggs are deposited on the underside of 1eaves infasted with mites. The maggots remain on the 1eaves, feeding on mitas. A total of 28 maggots were reared in the 1aboratory from last instar to adu1t form. The average

1ength of time spent in the pupal stage, at 80~, was 5·7 days. Fig. 9 shows a photograph of a 1ast instar maggot, with host mites, on the underside of a 1eaf. The number of generations par year is unknown, but is probably more than one, as the approximate time from oviposition to adu1t form is about 12 to 20 days. The maggot spins a light­ brown or almost white silken cocoon on the underside of 66.

the laar on whioh it has spent its larval lite. The cocoon is usually atiached to one or more leaf vains, at the junotion of the vains. The pupa aotually aœerges rrom underneath this silken eocoon. When the adult smerges, the pupal &kin is left attached to the leaf, close to the old eoooon. A photograph of this shed pupal skin baside the old oocoon is shown in Fig. 10. One instance was observed where no silken cocoon was construoted, and the adult emerged, apparently normal, from the unproteoted pupa. The first maggot was noted on May 23, and these predators were present from that date until about September

1~. It is possible that they overwinter as pupae under the silken ooooons, because the last six individuals coll­ eoted during September pupated normally, but no adults had emerged when winter arrived. A photograph of the adult fly is shown in Fig. 11. At least two speoies of Syrphid maggots have been noted feeding on adult mites. With one exception, all attempts to rear them on mites, or even a combination ot mites and aphids, were unsuccesstul. One adult fly sub­ mitted to the Syetematic Unit, Ottawa, has been identified by Mr. J.R. Vockeroth as Toxom.rus geminatus (Say). Fig. 9· Ceo1domy11d maggot and host mites on the underside of a laar. 68.

Fig. ~o. Old ooooon and empty pupal skin of a Oeoidamyiid predacious on mites. Fig. 11. Adu1t ~1y of Cecidomyiid maggot predaoious on mites. Some rearing cage other than the cotton­ stoppered vials would appear to be neoessary for suocess­ ful rearing. Observations imdicate that their main seareh for food is for aphids, and that any destruction of mites is incidental, and that their value as predators of mites is negligib1e.

XII. NEUROPTERA

In both 1950 and 1951, 1arvae of Neuroptera were round, in the field, feeding on Tetranychid mites. Eggs of Chrysopidae were found on many occasions attaohed by their stalks to leaves or twigs of currant bushes in­ tested with mites. Both eggs and larvae were brought in to the labora tory. The Chrysopid eggs hatched normally. A11 attampts to rear larvae on a diet of mites on1y, were unsueceasful. The larTae would readily feed on Tetranyobid mites, but always died betore pupating. Two reasons are advanced to account for this unsucoessfu1 rearing. It is possible that the sma11 glass vials used as rearing containers did not allow sufficient freedom tor the active larvae. A more likely reason is 71.

that the larvae need more sustenance than can be obtained from mites, or that the mites are not large anough to supply the necessary food. It was noted on more than one occasion, when observing the larvae with host mites, under a binocular microscope, that last instar Chrysopid larvae seem unable to impala the amall body of an adult mite on their mandibles. Attempts were made to rear Chrysopid larvae on a mixed diet of mites and aphids. Because the mealy plu. aphid was most abundant and most easily obtained at this tiœe, it was used in the feeding test. The larvae readily devoured both winged and wingless forms of this aphid. All the larvae in this test died before pupating. It appeared that the stieky excretions from the aphids, part­ icularly in the oonfined spaoe of a small glass vial, resulted in a gumming of the mouthparts, and the larvae were unable to continue feeding. In soma cases it appeared that the larvae were stuok on the sidas of the vial in a film of sticky substance from the aphids. When all rearing attampts had failed, adulte were oolleoted by sweeping mite-infested currant bushes. Specimens submitted to the Systamatio Unit, Ottawa, were identified by Dr. ~. Munroe as belonging to five species, 72.

Chrysopa plorabunda Fitch var. oalifornioa Coq. Chrysopa harrisii Fitch var. externa Hag. Chrysopa chi Fitch Hemerobius simulans Wlk. Hemerobius stismaterus Fitch On the basis ot numbers colleoted, Chrysopa chi is the most abundant speoies in Manitoba.

The most important mi te predaoious on Tetranyohid mites in Manitoba bas been identified by Dr. H.H.J. •esbitt ot carleton Collage, Ottawa, Ont., as Typhlodromus sp. (Iphidulus subgen.). In 1950 these mites were responsible for reduoing an infestation of ~· medanieli on a raspberry planting in Brandon to almost nil by June 30, and again in 1951 the s~e pattern was tollowed. Adulte ot Iphidulus were present on the newly opening leaves on May 9, and oviposition commenoed immediately, paralleling the devel- opment of the host mite. By June 30 very few individuals of either predator or host oould be found. In both years, -~. mcdanieli atterwards inoreased to almost economie statua on trees, shrubs, and flowers within the grounds containing the small raspberry planting, but Iphidulus remained very low in numbers for the remainder of eaoh year. Much the seme phenomenon oocurred in th a large currant blook at the Mental Hospital, Brandon, in 1950,

when a large population of ~· mcdanieli was reduced in the spring to negligible numbers by Iphidulus sp. To date it would appear that these predacious mites are most , active and most reproductive from early spring until about June 30, although suttieient individuals are present tor the remainder of the season, wherever host mites are round, to exert a considerable control by predation. More

detailed etudies of Iphidulus in Manitoba ~ght help to explain soma of the inexplicable fluctuations in populations of this predator.

rn 1951 1 Dr. Nesbitt identified a predaoious mite from Morden, Man., _as Typhlodromus lonsipilua Nes. No information is available as to whether or not this is the same species of Typhlodromus (Iphidulus) which is so abundant in Brandon and vioinity. A comparatively large, orimson mite is quite eommonly seen in the same habitat as the Tetranychid mites. It has been identified by Dr. Nesbitt as Anystis agilis Banks. When confined with the host mites, in the

laboratory, it readily consumes nymphe or adults of the Tetranychid mites. Several species of spiders oocur in close association with phytophagous mites, and at least soma of tham are believed to prey on the mites.

XIV • IMPORTANCE OF PREDATORS IN NATUR.AL CONTROL

No detailed data have been recorded in this study on the number of mites or mite eggs consumed by any of the predators. No satisfactory suggestions can be oftered as to how the importance of any pradator, or all the predators, can be evaluated. It is thought that any figures claiming so many mites consumed by one individual tor a stated tima interval are by and large meaningless, when oonsidering the whole oomplex relationship of pred­ ators to hosts, and of eaoh to its own environment.

At the present ti~ a great deal of work is being carried on in various parts of North America, on the importance ot predators in natural control. Workers in mbva Scotia are conduoting a thorough and oritioal study of this whole complex problem.1 and an outline of some of the work already accomplished may be found in Lord (1949,; 1949a). A brief review of the proltlem is given by Dr. A.M. Massee in the publication by Groves (1951). The importance of predators of mites may best be summed up l'tl:: 1-';,1· .

in the words of DtBaoh et al (~9.50) "It appears from . -- the stud:fes and observations harein reported that pradators are the most oommon and efficient factor regulating mite populations in the field." Observations made in Manitoba would agree with a further statament by the same authors

that "~requently, however, predators lag behind mites in population inereases and do not exert control until mite populations hava become more or lese damaging.n It is diffieult to assess the place ot predation amongst the natural control factors limiting mita popul­ ations in Manitoba, but it undoubtedly occupies an import­ ant role, as evideneed by the considerable list of known predators, and by the increase in mite populations when chemicals are used which are harmtul to the predators. Stethorus punctum and Iphidulus sp. are probably

the most important of the predaters. Their food is a~ost entirely confined to the host mi te. N.ext in order of importance might be the Ceoidomyiid maggot, and the two

thrips .!!• taure! and ~· sexmaculatus. The maggot is plenti­ ful in numbers and seems to prey only on the Tetranyohid mites. The two thrips may be more general in their teed­ ing habits, but the main part of their food appears to

oonsist of soma stage ot the mites. The Hemipteron and Neuropteron predators ara more inclimed to general feeding. Most of the predaoious plant bugs can be reared on a diet of mites only, but in nature readily devour a wide variety of Arthropod forma as food. Efforts to rear the laoe- Wing larvae on mites alone were always unsuocessful, and thesa larvae, particularly in their last instar, probably prefer aphids or other larger sources of food.

XV. SUMMARY

The most important Tetranychid mite causing economie damage to trees, shrubs, and flawers in Manitoba bas been identified as J!otetranychus mcdanfali (McG.). The Pacifie mite, Eotetranychus pacificus (McG.) is present at Morden, Man., in addition to !• mcdanieli. The important predators of !• medanieli are a small lady beetle, Stethorus punetum (Lao.), a mite, Iphidulus sp., a Ceoidomyiid maggot (speoies unknown), and the two thrips Haplothrips !aurai Hd. and Soolothrip! sexmaoulatus (Perg.). Other predaoious forms of lesser importance are named from the orders Coleoptera,- Hemiptera, Tbysanoptera, Diptera, Neuroptera, and Aeari. Predators were reared, in the laboratory, in small glass shell vials, stoppered wi th moistened ab~sorben t cotton. Predators were provided with tresh leaves daily, on which were the host mites. The bionomics of s. punotum are given in soma detail, whereas other predators are merely identified, and in some cases a few field notes added. s. punctum overwinters in the adult for.m. Tbere are at least two generations per year in Manitoba. More than two generations per year can be produced in laboratory rearing at constant and optimum temperatures. Description and habits of adults of s. punctum are given, with short notes on hibernation, flight, and copulation. Oviposition records were kept, in 1951, for seven overwintering females, and eight first generation females, of s. !unctum. One overwintering female laid 292 eggs in 72 day s. One first generation female laid 266 eggs in 45 day s. The greatest number of eggs laid by any one fe.ale, in the laboratory in a 24-hour period, was 24. Feœale beatles, which have never mated, will often lay infertile eggs. There is soma evidence that fertilization of overwintered females takes place the previous year, with no further copulation necessary. 78.

The egg or s. punotum is about 0.3 mm. long, 0.15 mm. Wide, and oval in shape. It is pearly white. Eggs are deposited on the underside or leaves infested with mites.

In the laboratory, eggs of ~· punctum failed to hatoh when held at constant tam~eratures of ;;o or llGoF for 25 days. Data were recorded tor development of eggs of

~· punctum. at constant temperatures of 6oo, 6.50, 70o, 75°, 80°, 90°, and lOO'T, in a study of tim.e (:t'or develop­ ment) x temperature (tor development). A t&llparature of 80°F appears to be most suitable tor incubation of the eggs. The times for development varied from an average ot 3 days at 100°F to an average of lL3 .6 days at 6

In laboratory rearing cannibalism by larvae is common, unless each larva is kept isolated. Forty-three larTae ot s. punctum were reared individually, in vials in the laboratory, at 80°Y, to pupae. Average duration of the first instar was 2.1 days; of the second, 1.4 days; of the third, 1.4 days, and of the fourth instar, 2.5 days. Average length of larval lite, at 8o0 r, was 7.4 days. At room temperatures, varying from ;oo-8o°F, average length of larval life was 1.3.3 days. rt appears that duration of larval lite is shortened oonsiderably by higher and constant tsmperatures, as opposed to lower and tluctuating room temperatures.

The last instar larva of ~· punotum pupates on the underside of the leaf where the larva has been feeding on mites. The average duration of the pupal stage at 80°F was 3.0 days. The average duration at room temper­ atures was 4.0 days for one period, and ;.1 days for another. An experiment was oonduoted to test the toxie1ty of methoxyehlor to adults of ~· punctum, and to compare the toxioity ot methoxyohlor with that of DDT. Adult beatles were exposed for two hours to leaves treated with these imsectioides. Of 70 beatles exposed to DDT, 33 died. or 70 beetles expoeed to methoxychlor, 42 died. An analysis ot variance showed that these differences were 80.

not significant. There was no mortality in the checks. A taxonomie comparison was made between adults ot Stethorus punctum, ~· picipes, and~· punetillum.

~o structural characteristios were noted other than those already shown in existing key•. Certain Coleoptera, other than .§.• mmotum., are predacious on mites. They are o:r minor importance as natural control factors, being mostly concerned with des­ truction of aphids. Of the Hemiptera, the two most common and most important predators are Orius insidiosus and Anthoooris musculus. Other known predators of mites in Manitoba are Ddaphnidia pellucida, Hyaliodes hart!, Hyaliodes v1tr1- pennis1 Plagiognathus obseurus, and Nabis :rerua. TWo important thrips predacious on mites in Manitoba ere HaplothriJ! taurel and SoolothriR! sexmaculatus. Aelothrips melaleucus is known from Morden, Man. An important predator is a Cecidomyiid maggot, believed to be a new species or Nycodiplosis. Syrphid maggots are occasionally predacious on mites. One specimen of Toxomerus gaminatus was reared. Five species of Neuroptera (three of Chrysopidae and two of Hemerobiidae} were colleoted as adulte from mite-intested currant bushes. Larvae of Neuroptera would 81..

readily prey on mites. The most important mite predacious on Tetra­ nyohid mites is a speoies of Iphidulus. It is capable, on occasions, of drastically reducing populations of

~· medanieli. Another mite, identified as Anystis agilis, is quite common. It is diffieult to assess the place of predation among the natural control factors limiting mite populations in Manitoba.

XVI. BI~LIOGRAPHY

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