Certain biological relationships between the parasite mella, and its host acrea

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Authors Adam, David Stuart, 1939-

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/318219 CERTAIN BIOLOGICAL RELATIONSHIPS BETWEEN THE PARASITE EXORISTA MELLA, AND ITS HOST ESTIGMENE ACREA

by • David So Adam

A Thesis Submitted to the Faculty of the

DEPARTMENT OF ENTOMOLOGY In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

1968 STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the Interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED I

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

J. A4% / T. F. WATSON ^

My sincere gratitude is extended to my advisor and thesis director, Dr, T. F. Watson, for his encouragement and advice throughout this study, I am greatly indebted to Dr, L, A, Carruth and

Dr, G, W, Ware for reviewing the manuscript and serving on my graduate committee. . . '

Special appreciation is expressed to Paul Johnson for his assistance in the laboratory. 1 also wish to acknowledge the assistance of Jeffrey Slosser, Gerald Jubb,

Jerry Phillip, and Robert Rush.

ill TABLE OF CONTENTS

Page

LIST OF TABLES oeeoeooooeooeeeooeooooe.oeeoeeo

ABSTRACT eeeeeedeeoeooeeeeoeeoeoftoeeoeeeoeeoeo "V11

INTRODUCTION« .... 1

MATERIALS AND METHODS4

RESULTS AND DISCUSSION...... 14

Adult Biology of Exorista me11a...... 14

Preoviposition Period...... 14 Oviposition Period.. 15 Mating Suooess.....o..15 ^ Sex Ratio...... oBee.ooooo.oe. ly Feoundity...... e.o...... iy Longevity @o.....e.oee..eoo...... 22 Size...... e.oe...... 22 Oviposition Behavior...... 24

Developmental Times of Egg, Larval, and Pupal Stages of Exorista me11a ...... 27

Success and Efficiency of Relative to Host Stage .e...... 33

Success and Efficiency of Parasitism Relative to Host Size...... 39

Supe rparas i t ism..,...... ,@... 0 8 .0 0 .. 48

SUMMARY...e...... 0 9 .o.O...... 0 .0 ...... 6 52

REFERENCES CITED o...... 6...... 53

iv LIST OF TABLES

Table page le Distribution by weight of later ins tars of Estlgmene acrea ...... 11 2 o Relationship of adult age to mating success of Exorista me11a 0 0 0 0 0 6 16 3® Relationship of the weight of Estlgmene acrea to the sex of Exorista

Hie JL JL8, 0 0 0 0 0 0 &O@ & 66 9 09 9 O06@ &06'0 0 0 9 0 0©®©18 Dry weight of Exorista me11a females in relation to total egg production „« 19 5® Adult longevity and egg production of Exorista me 11a in the laboratory »,<,<=<, 21 6e Effect of host weight and multiparasitism on length and dry weight of Exorista me11a adults ...... 23 ?. Time required for hatching of first Exorista me11a eggs on the host. Estlgmene acrea. at 75=2° + 1.6 F.... 28

8. Duration of larval development of Exorista me11a as affected by molting and survival of Estlgmene acrea ...... 30 9e Duration of combined egg and larval stages of Exorista mella in various sized Estlgmene acrea at 75=2 and 75 ® 7 Fo.ee.o...... 0 0 e ; 31 10d Stage of Estlgmene acrea at the time of larval Exorista mella emergence ... 34

v vi LIST OF TABLES— Continued Table • Page lie Success of the parasite Exorlsta me11a in relation to the stage of its host Estlgmene acrea ...... , 6 , * 36

120 Mean cumulative daily weight loss of twelve Exorlsta me11a puparla at 75-2 F„* * 37

130 Relation of puparial weight of Exorlsta me11a to weight of larvae and prepupae of Estlgmene acrea 38

14. Relationship of multiple puparlum production of Exorlsta me11a to size and stage of Estlgmene acrea...... e 40

15® Relationship of Exorlsta me11a puparlum mortality and multiple adult emergence to size and stage of Estlgmene acrea ...... 41

16. Influence of host weight of Estlgmene acrea on success of the parasite where parasite entry was observed oo.o.ooooo.o...... 44

17® A comparison of Exorlsta me11a success as a parasite on Estlgmene acrea when oviposition alone was noted and when oviposition plus parasite entry were noted. 46

15. Effect of superparasitism in Estlgmene acrea by Exorlsta me11a where parasite entry was observed ...... o...... 3® ABSTRACT

The adult biology of the tachinid , Exorlsta me11a (Walk,) was studied in the laboratory. Various aspects of the relationship of this parasite to the salt marsh caterpillar, Estlgmene acrea (Drury), were examined# The mean oviposition period of E, me11a females held at temperatures fluctuating between 72° and 78° F, was 24.8 days. The mean lifetime egg production was 150.6, but varied with female size, Longevity averaged

3800 days for females and 29.5 days for males. E. me11a eggs hatched in 48 to 192 hours at 75° F. Maggot developmental time averaged 6.4 days in those instances where the hosts did not molt after parasite entry. Where host molt took place, developmental time required an average of 12,9 days. At 75°» the mean developmental time in the pupal stage was 10.1 days.

When parasite er^try was observed, prepupal and pupal hosts successfully produced parasites twice as often as large larval hosts. Parasites utilized host prepupae as a food source to a much greater extent than host larvae and multiple emergence was much greater from prepupal hosts, Parasite success and multiple parasite emergence were alsc directly related to increasing host siSse. INTRODUCTION

Bxorlsta me11a (Walk.) is one of the more non-specific tachinid parasites of lepldopterous larvae0

Schaffner and Griswold (193*0 reared it from 25 host species in the northeastern United States„ Thompson

(1944) reported this parasite from 29 hosts in 7 families, while Simpson (1957) listed 4l hosts in 10 families0 The extensive range of this fly has been noted by

Coquillett (1897) and others. Simpson (1957) reported the occurrence of adult E. mella across the southern half of Arizona from

April to November. Taylor (1952) described it as one of the two most important tachinid parasites of the salt

marsh caterpillar, Estigmene acrea (Drury) in Arizona. Tachina (= Exorlsta) mella was described by

Walker in 184-9 but many synonyms were subsequently applied as this fly was recovered from numerous hosts in

North America, Thus Townsend (1908) referred to it as

Tachina clislocampae after it was reared from Cllslocampa

disstria. Lists of generic and specific synonyms are given

by Coquillett (I897) and by Sabrosky and A m a u d (1965)0 The European species Exorlsta larvarum (Linn.) was introduced into New England Between 1906 and 19270 Burgess and Crossman (1929) believed the imported and native were distinct species, but Aldrich (1931) felt that the two were identical. Schaffner and Griswold referred to the native as E. me11a in 1934, but confusion persisted until the two flies were placed into distinct species by Sabrosky and Arnaud (1965), Since the of this parasite is no longer considered questionable the present study was undertaken in the laboratory to clarify the Intricate host-parasite relationship between Estlgmene acrea and E. mella. This was considered as a prerequisite for more complex studies involving this host and parasite! Phases of adult £. mella biology studied included preoviposition and ovipositlon periods, mating success, sex ratio, fecundity, longevity, size, and ovipositlon behavior. Developmental times of egg, larval, and piipal stages of the parasite were recorded.

The success and efficiency of parasitism was measured by several criteria. The host stage when para­ sitized was related to percent parasitism success, as well as to multiple parasite emergence; The puparium-to-host weight ratio was used to measure parasite food utilization in larval and prepupal hosts. Host weight at parasite entry was related to percent parasitism success, percent puparial mortality, multiple parasite emergence, and parasite sizee A comparison was made of the difference in parasitism success between hosts where parasite entry was noted and where oviposition alone was noted. Superparasitism was delated to parasite size, parasite Utilization of f6b& and percent parasitism success ® MATERIALS AND METHODS

Larvae of the salt marsh caterpillar, Estlgmene acrea (Drury), used In this research were descendants of individuals collected in or near cotton fields in

September 1966 and July 1967, near Coolidge, Arizona, Most of the Exorlsta me11a (Walk,) used were descended from individuals emerging from the September 1966 collection of host larvae, while the remainder were descendants of flies captured in October, 1965 at a cotton field in Coolidge and furnished through the courtesy of Dr, Fye of the USBA laboratories in Tucson,

The medium used for the rearing of larval salt marsh caterpillars was the artificial lima bean-agar diet described by Shorey (1963), The methyl p-hydroxy- benzoate in this diet was generally adequate as a mold inhibitor but improvement in antimicrobial action was noted after the addition of formaldehyde, an ingredient in the diet of Shorey and Hale (1965)0

After several generations on the artificial diet a decline in fecundity and in numbers of pupating larvae was evident. Such a situation was noted by Vail,

Henneberry and Pengalden (1967) for salt marsh caterpillars reared on another diet although these authors felt that

' . . ■. ^ / V ' ' 4 " . '::' ' : ' / ' ' ' - \ ' - 5 seasonal change In daylight hours, rather than the diet# may have been responsible. Because of these difficult­ ies# encountered after several generations on Shorey’s lima bean diet# even under conditions of controlled photoperiod, an additional supplement of fresh alfalfa was given to late instar host larvae, Generally, the

growth rate and vigor of the succeeding larval generation improved following such a feeding, and disease was noticeably less of a problem. Such a supplement, used

every few generations as needed# appeared to be all that was necessary to maintain the salt marsh caterpillar

indefinitely on the Shorey diet.

In making the Shorey diet, 550 to 600 grams of dry lima beans were soaked in water for about 20 hours to yield 1200 grams of moist beans, The beans, plus 1200 grams of cold tap water, and all other ingredients except the agar were mixed in a 5"Quart Waring Blendor

until homogeneous. The agar was dissolved in the remain­

ing 1200 grams of water and heated to boiling before being placed in the blendor. The entire diet was blended

for several minutes and then poured into smaller contain­

ers for transfer to one-ounce plastic cups, About 300 one-ounce cups could be half filled with one batch of diet. Several hours were allowed for complete hardening of the medium before salt marsh caterpillars were placed in the cups, The diet cups were stored in a closed

plastic bag and held in a refrigerator for use as needede Caterpillars.less than 24 hours old were transferred to the. diet cups with a camel’s hair brush. The usual procedure was to place two larvae in each cup. Standard, center-tab cardboard lids were found to be

superior to other plastic or cardboard lids, which tended

either to restrict gas exchange or allow the diet to dry out too quickly. The larvae were removed when about one inch long and placed individually in cups of fresh diet. Some newly-hatched larvae were placed in 8-ounce squat-type cardboard containers approximately one-fourth

filled with diet. Less success was experienced in rearing with this method because disease spread more readily among the many larvae in each container® Late-instar larvae which received supplementary feeding of alfalfa were kept in 8-ounce cardboard

containers. Two larvae and a one-ounce cup of artificial

diet were placed in each container, and alfalfa leaves

were supplied daily. The caterpillars generally preferred the alfalfa over the artificial diet but would

switch to the latter as the alfalfa 1 became dry. - Salt marsh caterpillars were reared in temperature

controlled cabihets at 77 » 83®, and 86° F» Relative ' 7 humidity approximated $0% in the cabinets and 35% in the open laboratory* The larvae in the temperature cabinets were exposed to 15-hour photoperiods. No differences in mortality were detected between larvae kept in the cabinets and those kept in the open laboratory. Host pupae were held in one gallon ice-cream cartons at laboratory temperatures maintained between

72° and 78° P. Adults were removed daily after emergence. Handling of was simplified because they rarely fly in captivity. The adults were maintained in one gallon wide-mouth jars and exposed to naturally occuring photoperiods. Three strips of towelling, which extended from the top to the bottom of each jar, and circular pieces of towelling at the jar top and bottom, served as oviposltion and resting sites. Moths were fed a 10% sugar solution dispensed from a small vial held inverted on,the top of the jar by a piece of wire screening.

The strips of paper towel containing eggs were removed from each jar as needed and the eggs sterilized with a 4.7% aquenous Chlorox solution, followed by washing with a 18 20 (wto/vol.) aqueous sodluL thlosulfate solution. The sterilization was accomplished on filter paper placed in a funnel. Upon drying, pieces of . . . 8 towelling containing eggs were placed in haIf-pint Mason jars with fine-mesh screen lids and kept at 77° or 83d F» until the eggs hatched. One-ounce plastic cups were "preferrable for holding small numbers of eggs. Adults of E. me11a were maintained in the laboratory in two ways„ Individual pairs were held in cylindrical clear plastic Containers 4.5 inches high and 3 inches in diameter. Two-inch diameter holes covered

with fine-mesh nylon cloth provided aeration, A 3=5 inch

diameter filter paper placed in a petrl dish served as the

base. Water was applied to the filter paper at least once daily with a medicine dropper, and a sugar cube was placed in each container, A general laboratory culture 3 of flies was maintained in a 1 ft. , screened wooden- frame cage. Water was supplied by an inverted 6-ounce

jar placed over a filter paper in a petrl dish. Sugar cubes were provided as a food source e

All adult E, me11a were kept in the open laboratory. Longevity and fecundity records are there­

fore for temperatures fluctuating between 72° and 78° F.

Females producing viable eggs were considered to be

successfully mated. Total egg production was determined by counting the number of eggs laid on the hosts. Death

of a fly was assumed when all movement Ceased* Host larvae' to be parasitized by individual E e me11a females„ along with a one-ounce cup of artificial diet, were placed in the containers with the paired flies for 24 hours, Where possible, each female was given host larvae of all sizes to parasitize during Its lifetime. Several host larvae were generally placed in the large parasite cage at one time. Usually an adequate number Of eggs was deposited on the caterpillars within several minutes. Precautions were necessary where a specific number of eggs was required per host.

Excess eggs could be removed with fine-pointed forceps, but larvae generally had to be anaesthetized with carbon dioxide before this was possible, A total of 1200 host larvae was parasitized in the laboratory. The following information, where applicable, was obtained for each parasitized hosts date of oviposition, number of eggs, weight of host, date host became a prepupa or , date and number of puparia, and date and number of flies. Additionally, the following information was often recorded s date of first maggot entry into host, number of maggots enter­ ing, date of host molt, date of host death, weight of puparia, sex of fly, length of fly, and dry weight of fly, . Parasitized larvae were weighed with a torsion balance until a type H6 Hettier one-pan analytical balance became available. All hosts on which parasite entry observations were made were weighed to the nearest 0e1 mg® on the Mettler balance» Hosts were divided into 7.weight classes as shown in table 9 and in other tables. Where parasite entry was not observed, host weights were taken at the time of oviposition. Only those hosts weighing 50 to 100 mg, below the upper limit of each weight class were used, to allow for some host weight gain before parasite entry. All hosts on which parasite entry was observed were weighed within 24- hours of actual entry. Appreciable weight gain by hosts after parasite entry was very rare, and the circumstances under which it occurred are noted below, - Originally, the larval instar was intended to be used as a size criterion in the parasitization study but the extreme variability in instar~weight ratios, indicated in Table 1, prevented its use. The instars were determined by use of a powdered daylight flourescent pigment, placed on the caterpillar with a camel®s hair brush soon after each molt. The weights of Exorlsta me11a puparia and

- - I adults were neasured to the nearest 0,1 mg. All puparial weights used in compiling Table 13 ware taken

5 days after puparium formation because weight loss is 11

Table 1.— Distribution by weight of later Instars of Estlgmene acrea.

Instar

Weight (mg) _ - 3 4 5 6 7 _ 8 9 50-150 1 1 5 7 3 - l 150-300 - 1 1 3 1 1 l 300-500 ' - - - 5 3 1 -

500-700 - - - 2 5 3 -

700-900 - - - 3 8 3 - 900+ -- - 3 7 1 — 12 minimal at this time (Table 12)e Adult flies were allowed to dry for one week after death before they were weighed.

Host death was assumed when no movement resulted after prodding. No host death estimates were attempted for prepupae or pupae, Parasitized caterpillars were kept in temperature controlled cabinets maintained at 75•7° * 3•6° (369 readings) and 75°2 ± 1.6 0 (147 readings)e Standard deviations were computed as described by Wadley (1967)®

When host larvae died they were removed from the diet cups and placed in empty one-ounce cups. The parasites were kept in these cups„ at the same temperature, until they reached the adult stage. Parasite hatch and entry were recorded for a given 24 hour period by daily checking all eggs on all hosts under a Bausch and Lomb 0.7-30% stereomicroscope• Carbon dioxide anaesthesia was occasionally necessary to quiet extremely active larvae, The anaesthesia did not appear to have an adverse effect on the parasites * but was avoided where possible. Parasite entry was noted either by observing a maggot actively boring into the host or by observing the entrance hole containing the posterior end of the maggot. By itself, evidence of parasite hatch ffom the egg was nevei- considered 13 as proof of parasite entry. Separate records were kept where 1„ 2 „ and 5 or more E, me 11a maggots were; observed entering Individual caterpillars. Excess unhatched eggs were removed from the host when the desired number of maggots had entered. Parasite entry in the prepupal stage was achieved by parasitizing older larvae in the last Instar, RESULTS AND DISCUSSION

Adult Biology of ExorIsta me11a The phases of adult Exorista me11a biology investigated in the laboratory Included preoviposltion and oviposition periods, mating success, sex ratio, fecundity, longevity, size, and oviposition behavior®

) • Preoviposition Period

The mean preoviposition period of 32 female Eo me11a mated within two days of emergence at 72° to 78° F. was 3®2 + 1.1 days, while the time from mating

to oviposition was shorter but not specifically recorded*

The earliest viable eggs deposited by newly emerged and promptly mated females came between 48 and 72 hours. A

few virgin females were observed to oviposit a limited number of Infertile eggs during the same period.

Females over three days old at mating would often ovi­

posit non-viable eggs within 24 hours of mating, but

viable eggs were never observed before '24 to 48 hours

after mating. The gestation period of E, me11a therefore

approaches the reported minimum for the Tachlnidae,

which was 48 hours for Ptychomyla femota (Tothlll, Taylor* and Paine 1930)° Some preovlposltion periods 15 reported for other taohlnlds laying macrotype eggs include 6 to 12 days for Winthemla quadripustulata (Allen 1925)p a mean of 6.5 days for Phorocera hamata (Baldwin and Coppel 19^9), and a mean of 10 days for

Omotoma fumlferanae (Coppel and Smith 1957)o

Oviposltion Period The mean oviposltion period for Jk successfully mated E. me11a females was 24,8 + 6,7 days, with a range ^ \ of 13 to 38 days. The mean length of the oviposltion period of 0, fumlferanae was reported at 10 days (Coppel and Smith 1957)e As has been noted for some other tachinids, female E. me11a were sometimes found to oviposit fertile eggs within hours of death.

Mating Success

Some indication of mating success for 69 pairs of E, me11a adults is shown in Table 2, Although success was more likely when pairs were formed soon after emergence, a large number of failures resulted at all ages. No females produced viable eggs when mated when more than 16 days old, and no male older than 14 days was part of a successful pair. Mating success was much greater in the general laboratory culture consisting of many flies than it was among the isolated pairs.

Among many other tachinids the optimum time.of mating 16

Table Z»— Relationship of adult age to mating sucess of Exorlsta me11a..

Age of Age of Number of matings female male Not (days) (days) Suocessful Successful Total 0-2 0-2 , 13 7 20 3-6 3 3 6 7-23 2 2 4 3-6 0-2 9 5 14 3-6 1 .1 7-23 1 1 7-23 0-2 1 1 3-6 2 6 :8 7-23 1 10 11

\ occurs when the male is 1 or 2 days old and the females are just emerging (Clausen 1962)„ but females of Sturmla inconsplcua usually waited several days before mating (Webber 1932). Individual males of E. me11a were shown capable of fertilizing the eggs of several females, a common occurrence with most tachinids.

Females are known for multiple matings in some species, such as S. inconsplcua. but no direct evidence of this was obtained for E. me11a. -

Sex Ratio The sex ratio for E. me11a emerging from various sized hosts is shown in Table 3® There is no evidence that one sex has a competitive advantage over the other in relation to host size or superparas it ism. The female to male ratio of 521^8 is similar to that of some other species in which the sexes were distinguished easily.

The ratio for Phorocera hamata was (Baldwin and

Coppel 19^9 ) and that of Omotoma fumlferanae was 54;46

(Coppel and Smith)1957)®

Fecundity

Parasite egg production has been related to the dry weight of females in Table 4. It was generally observed in the present study that dry weights over

10 mg* corresponded to adult length over 10 mm. Flies 18

Table 3»"-Relationship of the weight of Estlgmene acrea to the sex of Exorlsta mella.

Weight of host Hq 8 of parasites observed (mg) Males Females

50-150 5 8 150-300 9 14 300-500 24 22 500-700 32 28 700-900 32 v ■ 33 900-1100 12 12

1100 + 41 48

Total 155 165 Ratio 48s52 19 Table 4.--Dry weight of Exorista me11a females in relation to total egg production.

Females laying Females laying viable eggs infertile eggs____ Weight No. of Mean no. No. of Mean no. flies of eggs flies °f eggs

l* 9-5.9 14 88,4 14 35.6 6o 0-9o 9 14 161.4 11 68,1

10.0-14.0 10 222 6 3 8 136,9 20 of this size would doubtlessly be preferred in the laboratory because of their higher reproductive potential# Observations of the mean lifetime egg production of Exorlsta me11a are summarized in Table 5® Mean lifetime egg production was 150 + 80,5 and 71,0 + 76,7 for females laying at least some viable eggs and no viable eggs, respectively. The highest number observed was 4-55 eggs laid by a fly which escaped before its total production was determined. Several females produced no eggs although they lived for over two weeks.

Flies laying macrotype eggs often have a capacity between 100 and 200 eggs, but in captivity a number are less productive, Omotoma fumiferanae averaged 25,2

(Goppel and Smith 1957) and Phorocera hamata 47,5 (Baldwin and Goppel 1949), while Ptychomyla remota never exceeded 69 eggs (Tothill et al, 1930), The mean daily oviposltion rates, based on total longevity, were 4,5 eggs for successfully mated ^ females and 3,4 eggs for unsuccessfully mated females.

The highest dally rate observed for an individual was

14.8 eggs per day. During the oviposltion period only, the mean dally egg production for successfully mated females was 6,0 eggs, Comparative oviposltion rates for Phorocera hamata were 2,0 eggs per day (Baldwin and Goppel 1949) and for Winthemla quadripustulata, 9*2 21 Table 5<-— Adult longevity and egg production of Exorlsta me11a in the laboratory®

Range Mean l/ Mean of lifetime Range 1/ No® longevity longevity egg of egg flies (days) (days) production production females laying viable 33 40®6 +17®2 17-61 150,6 33-321 eggs all females 71 38,0 + 12.4 11-68 113,6 6-321 males 67 29®5 + 11.0 7-57 - -

1/ does not IncjLude one female which laid 455 eggs before ""; escaping^ ■ . 22 eggs per day (Allen 1925)• Coppel and Smith (1957) noted that female Omotoma fumlferanae with higher rates of ovipositIon lived for shorter periods of time* This relationship was not observed to be consistently true for Exorlsta me11a*

The highest number of eggs laid by one Exorlsta me11a on a single salt marsh caterpillar host in a 24 hour period was 650

Longevity Observations of adult longevity of male and female Exorlsta me11a are summarized in Table 5= The longevity compares favorably with .that reported for other tachinids held in the laboratory* Male and female Winthemla qUadripustulata lived an average of

1O04 and 11»3 days, respectively (Allen 1925) and male and female Sturmia harrisinae lived an average of 7 and

13 days respectively (Smith, Dunn and Bosenberger 1955K Phorocera hamata lived an average of 3^ days (Baldwin and Coppel 19^9)» Madremvla saundersii ranged from 20 to 60 days (Coppel and Maw 195**) 9 but Omotoma fumlferanae never lived more than 39 days (Coppel and Smith 1957)®

Size

Table 6 summarizes observations on effects of superparasitism and host size on length and weight of 23 Table 6.--Effect of host weight and multiparasitism on length and dry weight of ExorIsta me11a adults.

No<> of Weight of host caterpillar puparia 50-500 500-1600 per mg mg caterpillar

a 0 Length of adult flies (mm) Noe‘ of Length No. of Length flies mm Plies mm

1 37 7 0 5 i 1 0 6 29 10.7 + 1.3 2-3 18 7.4 + 1.8 50 9.2 ± 1.5

4—3' 17 8.2 + 1.0 57 8.5 ± 1.3

6-9 - 50 8.5 ± 1.2 be Dry weight of adult flies (mg) No, of Dry weIghl .- flies mg _

1 14 11.1 + 3.1

2-3 23 7.9 ± 2.8

4—5 6-9 25 6.8 ± 3.0

I ' 24 E« me11a adultse As might be expected, a single parasite which developed in a sizable host became larger than those developing in smaller or superparasitized hosts„ The amount of food available to the parasite in the larval stage appeared to be the major factor in deter­ mining adult size„ Where superparasitism occurred in the smaller-sized hosts (Table. 6) the lack of decreasing parasite size might be explained by host-weight gain after parasite entry. This sometimes occurred when parasite development was slowed following a host molt, and will be discussed belowe Parasites emerging from a single host often Sifferred in size. For example, the following weights were recorded for flies which emerged from a single host larva8 2.9, 3.0, 8.4, 12.5, and 13 = 4 mg. The mean dry weight for 148 flies was 8.3 mg., and ranged between 1.8 and 17.6 mg® The adult length of E. me11a varied between 5 and 12 mm. In the laboratory. It has been reported as 7 to 13 mm. by Taylor (1952), 8 to 12 mm. by Simpson (195?) and 6 to 13 mm. by Essig

(1958). '

Oviposition Behavior Exorlsta me11a exhibits oviposition behavior quite similar to that of some other tachinlds. Females 25 showed little discrimination in choosing between previously parasitized and non-parasitized caterpillars» Taylor (1952) observed up to 25 eggs on field-collected salt marsh caterpillars, while on several occasions in the present study larvae in the laboratory were superparasitized to the extent of over 200 eggs, Taylor (1952) and Ainslie (1910) both noted that Exorlsta me11a females in the field were attracted to large host larvae. To observe whether this behavior took place in a confined containere one individually caged female was given a choice between one 100 mg, and one 600 mg, host larva for 12 consecutive days. New hosts were provided each day. On 9 of these days more eggs were laid on the larger larvae« A total of 109 eggs was deposited on the larger larvae while 29 were deposited on the smaller,.

In the larger cage containing many flies„ host movement was more important than size in stimulating the interest of females, An extreme example occurred when

5 last-instar host larvae were placed in this cage for

30 minutes. Upon removal 1, 3 * 5, 7» and 210 eggs„ respectively, were found on the 5 hosts. On another occasion 5 various-sized hosts received 0, 0, 1, 1, and 180 eggs, respectively, with a smaller larva being the one that was superparasitized. Host movement was 26 almost Invariably observed to be the stimulant to ovipositIon In such oases0 The flies would readily oviposit on active third-instar laryae weighing less

them 50 mge, although this was wasted ovlposltlon. That the motions of a host attract E. me11a to oviposit was observed by Ainslie (1910), and has been recorded for many other tachinlds. Webber (1932) noted that Sturmla Inconsploua was stimulated to oviposit even on inanimate material in motion. In the present study similar behavior was observed for E. mella, but such non-mobile objects as exuviae, dead flies, and the cage were also sites of wasted ovlposltlon, E. mella sometimes appeared to prod its host for signs of life, a characteristic which Allen (1925) noted for Wlnthemla quadripus tula ta„ Phorocera hamata appeared to be frightened off, rather than attracted, by movements of

its sawfly larval hosts (Baldwin and Coppel 19^9)• Tachinlds laying macrotype eggs are generally

not precise in choosing an area of the host for ovi­

posit ion, Hawboldt (19^7) found that Bessa selecta placed its eggs quite randomly, Wlnthemla quadripustulata

laid most of its eggs on the last two thoracic segments

(Allen 1925) and Ptychomyla remota deposited a majority

of its eggs on the last two thoracic and first few abdominal segments (Tothlll et al» 1930)0 In the present study observations indicated that Exprista me11a attempted oviposltion most often on the thoracic and first few abdominal Intersegmental membranes, but also frequently oviposited on the last abdominal segments and on the head capsule» setae and prolegs» The location of eggs on 67 hosts receiving but 1 or 2 eggs was nearly random» with numbers of eggs distributed from the first thoracic to the ninth abdominal segments as followss 7» 7» 8, 14, 10,, 5» 3» 7, 7, 6, and 2, respectively, Ainslie (1910) had found that E. me11a would almost invariably lay eggs on the crochets of Hemlleuca olivae because this host was extremely well protected by sharp setae0 Estigmene aorea, in common with many other hosts, is capable of crushing eggs placed on the last abdominal segments. This was observed in the present study.

Developmental Times of Egg, Larval. and Pupal Stages of Exorista me11a

Observations on the post-oviposltlon times required for the first Exorista me11a eggs to hatch on

202 hosts are summarized in Table 7e Only 24 hour units are shown in the table although more precise times of hatching were sometimes recorded. The earliest hatch at 75.2° + 1.6° F. was observed at $2 hours. A majority

of the eggs did not hatch until after 72 hours„ Butler, 28

Table 7 ,— Time required for hatching of first Exorista mella eggs on the hostg EsJblgmeni3 acrea, at • 75,2° ± 1,6° Fo

No, of Time in hours required :for hatching eggs on No, 48- 96" 120- 144- 168- host hosts 72 96~ 120 144 168 192

1 47 20 16 5 4 ■ 1 1

2“^ 31 10 15 4 2 0 0 5-15 82 36 29 ' 10 6 1 0 16 + 42 17 15 8 1 1 0

Total 202 83 75 27 13 3 1

Percent 41,1 37 01 13*4 6,4 . 1,5 0,5

i Bryan and Jackson (1968) found that all E„ me11a eggs maintained at 77° and 81° F. hatched between 48 and 72 hours and those maintained at 68° never required more than 116 hours to hatch# The discrepancies between the above results and Table 7 may have been caused by differences in the age of the females or the length of time the eggs were held before oviposltlon# Macrotype eggs of most species generally take between 2 and 4 days to hatch but extremes ranging up to 36 days for Omotoma fumlferanae are reported by Coppel and Smith (1957)» Duration of the larval stage, as measured from hatching to the time of puparium formation at 75«2° + 1*6° is shown in Table 8® As indicated in the table, hosts which molted after maggot entry often lived longer and caused delayed parasite development# In such instances the hosts often gained weight after parasite entry# Heavier than usual sclerotlzatlon of the sheath about the first instar maggots was plainly visible in lighter hosts and may have contributed to the delayed develop­ ment# Hawboldt (1947) has noted a similar occurance for Bessa selecta, but did not relate it to host molt#

Observations on the duration of the combined egg and larval stages for different sized hosts at

75o2° and 75®7° are summarized in Table 9® To an ektentj, the Increased developmental times for parasites 30 Table 89 “—Duration of larval development of Exorlsta me11a as effected by molting and survival of Estlgmene acreae

Time from Duration Status of hatching of of larval host after parasite to stage of parasite death of host parasite entry No, of Days to No, of Days to hosts host parasites puparlum death formation molting observed 13 7.8 + 3.9 24 12,9 ± 3.7 ') no molting observed 91 3.3 ± 1.9 205 6 ® 4 + 2 e 0 31 Table 9 e*"l)tH‘ation of combined egg and larval stages of Exorlsta me11a in various sized Estlgmene acrea at 7 5 and 75,7 F,

Mean Meight developmental of hosts No, time Range [mg (days) (days)

50-300 , ■. . 65 12.4 6—34 300-500 82 11.1 7-21

500-700 175 10,6 7-20 700-900 109 10,8 7-18

9.00-1100 55 9*6 7-16 1100 > 100 8.8 6-19 32

In smaller hosts probably reflects the delayed development shown In Table 8, for the smaller hosts were most often the ones to molt after parasite entry. This relationship does not appear to be common in other parasitic which have been studied. Mote, Stearns and Dimick (1931) found that the tachlnid Digonichaeta septlpennls develop® ed in a shorter period of time in smaller as well as superparasitized hosts. Similar results were found for such Hymenoptera as Pimnla turlonellae (Arthur and Wylie

1959), Braeon green! (Pramanik and Choudhury 1963) and Trichogramma .japonlcum (lyatomi 1958). The mean developmental time of 10.5 days for Exorlsta me11a eggs and larvae observed in the present study approaches that which would be expected according to the work of

Butler et al. (1968).

At 75»2°, the mean length of time for 151 Exorista me11a puparia was observed to be 11.0 + 0.7 days, which is also comparable to the results of the above authors. Developmental time for puparia was consistent, regardless of host size.

In 48 of 49 instances where both sexes developed in the same host, the. larval developmental time in days was the same for both male and female parasites. However, under similar circumstances as puparia, over half of ths females took one day longer than the males 33 to emerge» a condition which is„ according to Clausen (1962), common in the Tachlnidae e ' The mean total development time, from egg to adult6 for 520 parasites reared at 75*2° and 75*7° was 20,5 days.

Success and Efficiency of Parasitism Relative to Host Stage The stage and size of the salt marsh caterpillars at the time of parasite entry and emergence are compared in Table 10, A large majority of parasites entering larval hosts weighing up to 700 mg, also emerged from the larval stage. Over 60% of those entering larger host larvae emerged from prepupal or pupal hosts.

Relatively few of the parasites entering host larvae passed through the prepupal stage and emerged from host pupae, but 79% of those entering the prepupal stage emerged from the pupa of the host. Approximately 9% of the parasites pupated inside the host and emerged from the host as flies. These observations contradict

Burgess and Crossman (1929) who stated that Exorlsta me11a always pupated within the body of the caterpillar or pupa,. Butler et al, (1968) „ investigated paraslt~ ization of late instar salt marsh caterpillars and ' reported that approximately 15$ of the parasites remained within the host, 39$ emerged from larvae? Table 10,--Stage of Estlgmene acrea at the time of larval Exorista mella emergence e

Host weight at time of parasite Host stage at parasite emergence entry No. of (mg) hosts Larvae Prepupae Pupae larvae No. i No. % No.

50-150 35 35 100 0 0 0 0 150-300 41 40 97.6 1 2.4 0 0

300-500 57 49 86.0 7 12.3 1 1.8

500-700 60 44 73.3 11 18.3 5 8.3

700-900 42 15 35-7 24 57.1 3 7.1

900 + 46 15 32.6 21 45.7 10 21.7 prepupae

,62991/ 64 - - 19 29.7 45 70.3

Total 345 198 57.4 83 24.1 64 18.5

1/ average weight. 20$ from prepupae, and 26$ from pupae e Observations on the effect of host stage on parasite success are summarized in Table 11. Based on work discussed below, host larvae weighing over 400 mg. were considered more suitable hosts than smaller larvae, Because parasite entry was observed in all instances and none of the three groups was superparasitized more than the others, it must be assumed that larvae are inferior to pre pupae and pupae as hosts..

To obtain other evidence on the suitability of the host stages, parasite efficiency in utilizing the host food source was measured. The total weight of puparia emerging from each host was related to the weight of the host at the time of parasite entry, based on caterpillars producing at least one puparium. The time of weighing the puparia was critical for, as shown in Table 12, nearly 20$ of the original weight was lost in the two days following puparium formation. All puparia were weighed at 5 days or had weights corrected to correspond with 5-day-old puparia in order for the weight loss to be consistent in all instances. Table 13 shows the results of comparing the puparia to host weight ratios for parasitized host larvae and prepupae. Host prepupae ^ including some which became ptipae, allowed a single parasite to utilize as 36 Table 11* — Success of the parasite Exorlsta me11a in relation to the stage of its host Estigmene acrea0

Host N u# er _hps%ielding of^hosts Stage Fuparla yielding at death Humber Adults flies

larva 68 35 30 44.1 (over 400 mg)

prepupa 40 36 81.8

pupa 31 2? 27 87 * 1 37 Table 12.— Mean cumulative dally weight loss of twelve Exorlsta me11a puparla at 75*2 F.

Days after puparlum Cumulative percent formation weight loss____

1 13.1 + 2.9 2 18.9 + 3.4

3 19.7 + 3.5 4 19.8 + 3.7 5 20.3 + 3.2 6 21.1 + 3.1

7 22.3 + 3.3 8 23.9 + 3.3 38

to weight of larvaei and prepupae of Estigmene acrea. '

Estlgmene acrea Puparla of E. mella Stage at Av. Mean wt. Ay. % of parasite No. weight per host no. per host entry observed (mg) (mg) host weight

a. Entry by one maggot prepupa 12 673.3 85.9 1.0 12.8 + 4.1

b. Entry by 2 or more magKots larva 28 811.4 90.8 1.9 11.2 + 5.4 prepupa 23 615.7 , 194.4 4.5 31.6 + 9.7 39 much of their body weight as superparasitized host larvae allowed multiple parasites to use» Superparas it* ized prepupae were utilized to a much greater extent by the developing parasites, with the result that more puparla per host resulted from smaller hosts. As might be expected, the largest Exorlsta me11a larvae developed when no competition was present,. Single parasites emerg­

ing from superparasitized hosts were smaller, however, indicating that the. unsuccessful competitors has an effect

on the survirors,-

Further evidence on the relative suitability of larval and later stage hosts for multiple parasite development is shown in Table 14, The stages at parasite

emergence have been distinguished only in the 500 to 700 mg, weight classe Nearly twice as many puparia resulted

per prepupae or pupal host as per larval host of the same size, . Table 15 indicates that the mortality of puparia emerging from host prepupae and pupae was lower

than for those emerging from larvae®

Success and Efficiency of Parasitism Relative to Host Size <

Multiple Exorlsta me11a emergence from single host has been noted by several authors, Schaffner and Griswold (1934) usually obtained one or two E, me11a

flies but recorded as many as 11 from one host (species 40

Table 14.— Relationship of multiple puparium production of Exorista me11a to size and stage of Estigmene acrea.

No. of hosts Av. no. of Host weight producing No. of puparia (mg) puparia puparia per host

50-150 . 33 38 1.2 150-300 37 39 1.1 300-500 54 84 1.6

500-700-/ 36 63 1.8 500-700-' 32 108 3.4 500-700 (combined) 68 171 2.5 700-900 46 110 2.4

900-1100 22 56 2.5

1100 + 33 115 3.5

Total 293 613 2.1

1/ parasites emerged from host larvae• 2/ parasites emerged from prepupae and pupae. Table 15#— Relationship of Exorlsta me11a puparlum mortality and multiple adult emergence to size and stage of Estlgmene acrea.

No. of Av. no. Host Percent hosts of flies weight No. of No. of puparla producing per (mg) puparla flies mortality flies host

50-150 38 18 52.6 14 1.3

150-300 39 ‘ 23 41.0 22 1.0 300-500 84 58 31.0 40 1.5

500-700-/ 63 44 30.2 29 1.5 500-700-/ 108 88 18.5 31 2.8 500-700 (combined) 171 132 22.8 60 2.2 700-900 110 99 10.0 45 2.2

900-1100 56 49 12.5 22 2.2

1100 + 115 110 4.3 32 3.4

Total 613 489 20.2 235 2.1

1/ parasites emerged from host larvaee 2/ parasites emerged from prepupae and pupa. 42 not specified) in the northeastern United States6 Taylor (1952) reared between one and 4 E„ me11a from field collected salt marsh caterpillars in Arizona.

Butler et al,. (1968) obtained one ,parasite from 59%t 2 from 23#, 3 from 10%, 4 from 6% and 5-7 from 2%, of the Salt marsh caterpillars reared in the laboratory. In the present study the most flies recorded from one host was 8, although 9 puparia per host were observed on several occasions.

Much evidence exists that multiple tachinid development is related to host size, but little of it is quantitative * Webber (1932) always obtained one Sturmia inconsploua from the host Meodlprion dyarl but up to

7 emerged from the larger Forthetrla dispar. Dowden (1934) was able to rear fewer Zlnlllla llbatrlx in Forthetrla dispar than in the larger Bombyx mori. Similar results were found for different hosts of Winthemia quadrlpustulata by Allen (1925)« The mean numbers of puparia and adults of Exorlsta me11a, observed in various sized hosts producing at least one parasitej is shown in Tables 14 and 15. The effect of host stage was previously notedp and a fairly direct relationship exists between host weight and multiple emergence. As mentioned, a large portion of the hosts weighing over 700 mg. attained the prepupal or pupal stage, A table giving results entirely from larval hosts would show a more conservative picture of multiple parasite emergence0 Ezorlsta mella puparial mortality decreases considerably with increasing host size, as shown in Table 15» This further substantiates other findings on the Ineffectiveness of smaller salt marsh caterpillars as hosts0 The above tables Indicate the importance of using hosts weighing over 1100. mg. when large quantities of E, mella parasites are. to be reared in the laboratory. Observations on parasitism success, as measured by the number of hosts producing at least one puparium and one fly, are reported In Table 16. Although parasite entry was noted in all cases, success did not exceed 42$ for those hosts weighing under 300 mg., nor did it exceed 78$ for larger hosts„ Little information exists in the

literature concerning similar parasitism success rates

for other tachlnids reared in the laboratory. Tothill et al, (1930) found that 57*2$ of Levuana irldescens

larvae in the last 2 ins tars produced adult parasites when exposed in cages, to Ptyohomyla remota. .Observations on the median number of eggs laid

oh hosts producing pupania and on hosts producing flies are reported in Table 16. The mean was not used as an Table 16.— Influence of host weight of Estlgmene acrea bn success of the parasite Exorista me11a where parasite entry was observed.

No. hostsxwith Percent of hosts Median no. observed entrances of where parasites esses t>er host parasite larvae developed Height of host All Hosts producing Producing To To (mg) hos ts puparia flies Total puparia flies puparia adults

50-150 ■ 11 5 3 49 *14, 9 28,6 18.4

150-300 8 8 7.5 55 23 16 41.8 29.I

300-500 10 10. ;; 9*5 50 35 28 70,0 56,0 500-700 7 7 7 ' 89 65 58 73.0 65.2

7OO-9OO 7 9 10 45 35 33 77.8 73*3

900 + . 9 13 13.5 41 31 30 75*6 73,2

Total 329 203 174 61.7 52,9 45

index because several instances of extreme superparasitism would have given a misleading picture of the number of eggs on most hosts. It is apparent that oviposition of more than a few eggs caused destructive superparasitism only in the smallest host larvae, For larger hosts, a . : j median of between 7 and 13.5 eggs was present on hosts successfully producing pupal and adult parasites. The

median number of eggs on hosts weighing 900 mg. and over

was actually greater in successful hosts, an indication

that fewer numbers of parasites per host did not mean that parasitism was more successful. Complete recovery by several large hosts was noted following single para­ site entry. Host molting was not observed in these instances and the possibility exists of an internal host

defense mechanism. A comparison of parasitism success when parasite entry was not observed with that when entry was observed

is shown in Table 17. Female Exorista me11a used for

' oviposition in the former group had previously been

observed to lay viable eggs at least some of the time.

Success for the group in which entry was observed ranged

from approximately 8 to 26 percent higher than the corresponding weight classes of the other group.

Several causes of inefficient parasitism between 46, Table 17»""A comparison of Exorlsta me11a success as a parasite on Estigmene acrea when oviposition alone was noted and when oviposition plus parasite entry were noted.

Parasites not Parasites observed entering observed entering Weight No, No, of host hosts hosts (mg) :;:Noe yielding % No, yielding % hosts flies success hosts flies success

50-150 161 13 8,1 49 9 18,4 150-300 83. 17 20,5 55 16 29,1

300-500 79 29 37.2 50 28 * 56.0

500-700 61 24 39°$ 89 58 65,2 700-900 ■ 46 30 65,2 45 33 73.3 900 + 76 40 52,6 41 30 73.2

Total 506 153 30*2 329 174 52,9 w oviposition and the time the parasite larva enters the host were noted by Hawboldt (19^7) for Bessa seleota. These included? (1) eggs sloughed off with exuvia, (2) maggots sloughed off with exuvia, (3) maggots dead in eggs and (4) maggots dislodged from the surface„ In the present study, the following additional factors were observed to reduce the effectiveness of Exorlsta me11a s

(5) infertility of eggs, (6) eggs crushed by host, (7) poor placement of eggs and (8) maggots unable to penetrate host integument. Another factor which undoubtedly caused some ineffectiveness between larger hosts of the

two groups in Table 17 was that relatively more prepupal, rather than larval, hosts were used under the 69parasites observed entering" heading®

All of the first five instars of salt marsh

caterpillars reared on Shorey and Hale0s (1965) diet by Malik (1967) averaged less than 3.0 days per instar at

77° F e Because Exorlsta me11a eggs hatch no earlier than 48 hours at this temperature, a majority of randomly

parasitized hosts of the first five instars would be

expected to molt before parasite entry. In one sample

of 384 caterpillars weighing under 700 mg. and parasitized in the present study 12% molted within 24 hours. Undoubtedly many more hosts molted before the parasite eggs hatchedf More extreme effects of host molt on 48

E. me11a parasitism were noted for field collected Porthetria dispar by Forbush and Fernald (1896). Of

235 larvae collected with one to 33 eggs on each, 226 molted and emerged as moths while only 4 E, me11a emerged. In the laboratory, the safest procedure for avoiding this inefficiency was to parasitize last instar hosts. Owing to the lengthy prepupal period of the last instar, these hosts seldom escaped parasitism by molting.

Specific reasons why all optimum sized hosts were not successful in producing parasites after observa­ tion of parasite entry were not determined. Some general factors which were believed to be important include» host recovery from single parasite attack, superparasitism, relative inefficiency of the larval hdst stage and temporary dietary deficiencies and disease problems of , the host.

Superparasitism For a majority of ta. chin ids only one individual develops within a host. When superparas it ism occurs the extra maggots are killed through overcrowding, starvation, or combat (Clausen 1962). For those species where multiple development is possible, the size of the host food supply is often associated with the size and numbers of parasites capable of developing. 49 As previously noted, Tables 6 and 13 relate Egorista me11a size and utilization of food supply to superparasitism„ Tables 14 and 15 relate multiple parasite development to host size and stage and Table 16 indicates that more than a few eggs caused destructive parasitism only in very small hosts. Some indication of, the effects of increasing superparasitism on similar sized hosts is shown in Table 18. Although the chances of at least one parasite developing successfully appear to Increase with super- parasitism, some observed negative aspects are not shown In the table. Parasite size and the number of multiple emergences per host were greatly reduced when excessive competition occured. Superparasitism was successful more often when parasite development took place in the prepupal or pupal, rather than larval stage. In one instance a single stunted adult parasite emerged from a host prepupa which had received over 200 eggs, from which many maggots had been observed to enter the host. The largest parasites were produced where there was no competition. The greatest percent of successfully parasitized hosts occurred when there was abundent competition between parasites. For laboratory rearing, with compromises between the combined desired 50

Table 18.--Effect of superparasitism in Estlgmene acrea by Exorista me11a where parasite entry was observedo

Mean Hosts Hosts weight producing puparia producing flies No# Wo# of host eggs hosts (mg) number percent number percent ll/ 45 679.2 24 53.3 22 48.9 21/ 17 555.3 10 58.8 8 47.1 3-41/ 18 624.6 10 55.6 9 50.0

5rl5~/ 94 ' 569.5 61 64.0 52 55.3 l6~3oS/ 31 724.3 22 71.0 20 64.5 30 +&/ 12 628.6 11 91.7 10 83.3

1/ parasite hatch and entry observed from all of the eggs#

2/ parasite hatch and entry observed from some of the eggs# 51 characteristics of large parasite size, multiple parasite emergence„ and a large number of hosts producing parasites^ optimum parasite production appeared to occur when a range of from 5 to 15 viable eggs were deposited per host* SUMMARY

Adults of Exorlsta me11a were studied in the laboratory at temperatures ranging between 72° and 78° F, The preoviposition period lasted 3,2 + 1,1 days and oviposition period 24,8 + 6,7 days. Successful matings resulted more often from newly emerged adults.

The female«~to~male sex ratio was $2s^8 and was unaffect-

) ed by host size. Females laying viable eggs had a mean lifetime egg production of 150,6 + 80,5, ranging up to 455» and egg production was related to female size. The mean daily egg production during the ovlposltlon period was 6,0, Female longevity was 38,0 + 12.4 days and male-longevity was 29,5 + 11,0 days, Parasites which developed in smaller or superparasitized hosts produced smaller adults, Ovlposltlon behavior was quite similar to that reported for other tachinlds laying macrotype eggs,

Developmental times for eggs„ larvae, and pupae, were determined at one temperature level. At

75,2° + 1.6° F., a majority of the first eggs which hatched on hosts did so after 72 hours» Where host molting did not occur after parasite entry* larval . . - " .. . . - ■ development^ required 6,4 + 2,0 days. Host molting

■ ■ "52 . 53 after parasite entry delayed larval developmental time to 12e9 ± 3»7 days. Egg-plus-larval developmental time took longer in smaller hosts, and averaged 10,5 days. The pupal stage lasted 11,0 + 0,7 days, and was consistent regardless of host size. About half of the females took one day longer than males for pupal development,

A majority of parasites entering smaller host larvae, weighing less than 700 mg,» emerged while the host was still in the larval stage, A majority of those . parasites entering larger host larvae emerged from prepupae or pupae of the host. Parasitized hosts reach­ ing prepupal and pupal stages produced adult parasites twice as often as those remaining in the larval stage, although parasite entry was noted Ip. all cases. The puparla-host weight ratio, expressed as a percentage, for host larvae averaging 811A mg, was 11,2 + 5 A#, while for prepupal hosts averaging 6l5®7 mg, it was 31=6 + 9«7%9 indicating greater utilization of the prepupal food source. Almost twice as,many parasites resulted from prepupal as from larval hosts of the same size,

A direct relationship was found between parasite emergence and host weight. Hosts of over 1100 mg, which 54 were successfully parasitized produced an average of 3«4 flies per host® Puparial mortality greatly decreased with increasing:host size. Successful parasitism where parasite entry was observed, increased with host size but never exceeded 77«8$ of the hosts„ Successful para­ sitism was consistently greater in those hosts where maggot entry was actually observed. The greatest loss of efficiency between oviposition and parasite entry occurred when eggs were molted off with the host exuviae0

A degree of superparas it ism was shown to be beneficial in rearing the parasites in the laboratory. The puparium-to-host-weight ratio Increased greatly when several parasites developed in a host, although single parasites developing in hosts were larger. A median of more than several eggs per host caused destructive super- parasitism only in those hosts weighing less than 150 mg. Compromising, on the desired characteristics of large parasites, multiple parasite emergence, and a high percent parasitism, the optimum number of viable eggs per host was 5 to 15. The percent of hosts producing at least one adult parasite increased in proportion to the number of parasites entering, but extreme superparasitism caused stunted parasites and fewer cases of multiple parasite emergence^ / REFERENCES CITED

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Arthur, A. P. and H, G. Wylie, 1959* Effects of host size on sex ratio, development time and size of Plmpla turlonellae (L.) (Hymenopterat Ichneumon- idae)• Entomophaga 4i 297-301.

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Wadley, F. M. 1967. Experimental Statistics in Entomology. Graduate School Press, Washington, . ' D«C. 133 PP® Webber, B« T. 1932. Sturmla inconsplcua, a tachlnid parasite of the gypsy moth. J. Agr. Bes. 458 193-208,