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Inhibitory regulation of corpus allatum activity in mosquitoes
J. /?r.vrcr Pl!,.>io/.. Vol. 27. No. 10. pp. 651-654, Prrt~rccl it1 Grerrr Brituin.
INHIBITORY
1981
0022-t 7Y0.8 I I0065 1_94$02.(Jl).(~ ( I YX I PrySlrnrl~ll PII,.\.\ Lrr/.
REGULATION OF CORPUS ACTIVITY IN MOSQLJITOES
ALLATUM
P. A. ROSSIGNOL, F. M. FEINSOD* and A. SPIELMAN Department
of Tropical
Public Health, Harvard School of Public Health. Boston. MA. 02 I 15. U.S.A.
665 Huntington
Avenue.
Abstract In order to determine whether juvenile hormone (JHt in mosquitoes is regulated by ovarran inhibitory feedback. we implanted JH-sensitive pupal ovaries into aJult mosquitoes and observed subsequent ovarian maturation. Removal or destruction of resting-stage ovaries (previously JH-stimulated) resulted in J H-stimulated development of implanted pupal ovartes. Ablation experiments demonstrated the ovary-corpus allatum sequence of maturation, and application of exogenoushormone analogs contirmed that development of implanted pupal ovaries is JH-dependent. Inctdental observations indicated that ovaries of preapolytic pupae produce a hormone that causes more mature ovaries to degenerate. We concluded that corpus allatum activity in Ardes aqqpri is regulated hy ovarian feedback inhibition. K(j), UOid bzde.~: Juvenile hormone. mosquitoes. reproductron. corpus allaturn. ovartes
INTRODUCTION factors regulate juvenile hormone (JH) in insects as diverse as cockroaches, bugs and flies. JH synthesis is reduced in a cockroach through an ovarian feedback mechanism apparently involving 20-hydroxyecdysone (STAYet al.. 198OJ, and the same hormone may behave similarly in a kissing bug (GAKCIA it al.. 1979). In addition, the corpora allata regulate previtellogenic development of the housetly and their activity is suppressed by an oostatic hormone deriving from vitellogenic ovaries (ADAMS et al., 1968: ADAMS. 1970). But, this interpretation is controversial (LEA. 1975; PAPPAS and FRAENKEL, 1978). Eggs of mosquitoes are produced in synchronous clutches. each stimulated by a meal of blood which induces the most mature follicles to develop synchronously, while less mature follicles await the next maturational stimulus. At least two hormonal complex pattern of coordinate this signals development. Follicles becomecompetent to sequester vitellogenin following stimulation by JH (ANDERSON and SP~LMAN, 1971; G$ADZ and SPIELMAN, 19731, but do not develop further until the mosquito takes a meal of blood. Thereafter. eggs mature independently of JH-stimulation (LEA. 1969). Two days after each meal of blood, JH stimulates the most mature follicles to become competent to sequester vitellogenin (FEINSOD and SPIELMAN, 1980a). Normally only the most mature follicle within each ovariole undergoes and this presents a problem of vitellogenesis, non-regulated coordinating JH-regulated and maturation. A meal of blood. through hormone-stimulatory mechanisms. coordinates vitellogenic development but the coordinating mechanisms for JH-regulated INHIBITORY
secretion
* Present address: Cleveland Metropolitan General Hospital. Department of Internal Medicine. 33Y5 Scranton Road. Cleveland. OH 44109. USA. 651
development is unknown. The simplest model requires that an ovarian hormone regulates allatum activity through feedback inhibition. Accordingly. we determined whether JH-stimulated ovary or ovaryassociated tissues affect JH activity. In addition. we examined the converse hypothesis that such tissues. not exposed to juvenile hormone. may stimulate JH activity.
MATERIALS
AND METHODS
At&s uqypri mosquitoes (Bahama strain) were used throughout this work. Origin of the strain, rearing procedures. and techniques for recording ovarian development have been described ( FEKLCOII and SPIELMAL 19XOb). At the beginning of each experiment. adult mosquitoes were 34 days postecdysis and non-mated. LCIM’S(1961) saline was the medium used for dissection as well as implantation. Mosqutloes were allatrctomt~ed as descrtbecl 1~) LEA (1963). In order to oppress the ovary against the abdominal wall. mosquitoes, otherwise provided with raisins. were permitted to gorge on IO”,, sucrose. Mosquitoes w’ere restrained in a piston device (SPIELMANand WONG. 1973). A lateral incision m the pleural membrane between the 7th and 8th abciominal segments was made using tinely honed forceps. The underlying ovary was grasped and gently drawn caudally. thereby breaking the common oviduct and permitting both ovaries to be withdrawn through one incision. A JH-analog (Altosid; Zoecon. Palo Alto. CA) wlas applied topically X0 ng in 0.X /iI 01‘ acetone/mosquito. Our JH-bioassay used ovaries removed from pupae. The presence of scales on the pharate adult was used to distinguish postapolytic from preapolyttc pupae. Ovaries were injected via a tapered capillary tube into thoraces of adult mosquitoes restrained in the piston device. In order to prevent excised ovaries from
P. A.
ROSSIGNOL, F.
M.
FEINSOD AND A. SPIELMAN
Table I. Development ofovariesremoved from pre- or postapolytic pupae and implanted into udult. lmale mczsqultoes with ovaries rcmovcd OI-with overlying pleura perforated Developmental stage of PUpa donating
I ength of follicles in freatment
ovarian impktnl
Implanted
)
IN0
ovaries
(“,, 2 70 jm~) (“,, degenerated)
perforaled
?(I 72
7.5 IX
Okaries removed
I2 ‘0
X? 711
Ovaries removed
LO
60
!I,
15
Plellr2
Pleura
resident ov3rIc:,
55 5
perforared
sticking to the walls of capillary tubes, albumin was added to the saline solution. later. implanted ovaries were removed measured using an ocular micrometer.
I”,, bovine Four days and then
RESULTS In a preliminary experiment, we determined whether ovaries, not yet stimulated by JH, may induce JH production. Since JH activity is detectable soon after adult ecdysis (GWADZ and SPIELMAN, 1973), we reasoned that pre-ecdysial pupal ovaries should be maximally stimulatory as well as responsive to JH. Accordingly, using apolysis as an additional preecdysial marker, we transplanted ovaries from pre-and postapolytic pupae into non blood-fed mosquitoes. II such treatment stimulated JH secretion, transplanted ovaries would develop to the previtellogenic stage ol arrest. Surprisingly, implanted postapolytic ovaries generally failed to develop, while those from preapolytic pupae developed to the previtellogenic stage of arrest (Table Ii. We noted that ovaries native to host mosquitoes more commonly degenerated in the presence of preapolytic pupal ovaries. In cases of extreme degeneracy. ovaries were composed largely of oviduct and trachioles: follicular tissue was not apparent. It may be that this functional ovariectomq promoted development of implanted ovaries by removing inhibitory factors. This finding led us to determine whether loss of ovarian could explain why implanted tissue
preapolytic pupal ovaries developed further than do postapolytic ovaries. Mosquitoes were ovariectomized and, 1 day later, pupal ovaries were implanted. Virtually all such pre- as well as postapolytic pupal ovaries developed to the previtellogenic stage of arrest (Table I), and this indicated that removal of JHstimulated ovaries may stimulate subsequent JH production. We then compared development of postapolytic pupal ovaries in ovary-intact vs ovariectomized mosquitoes. In this manner, we confirmed that ovariectomy promotes development of implanted pupal ovaries (Table II. Taken further, these experiments indicate that JH activity is not stimulated by JH-deprived ovaries. We tested the alternative hypothesis that ovaries in the previtellogenic stage of arrest may inhibit JH activity. In one experiment. mosquitoes were allatectomized and. I day later. ovariectomized. The following day, postapolytic pupal ovaries were implanted. Such implanted ovaries generally failed to develop, while similar ovaries implanted into ovariectomized mosquitoes having intact corpora allata (or overlying pleura perforated) developed to the previtellogenic stage of arrest (Table 2). In this experiment. allatectomy followed ovariectomy. In a companion experiment. the order of tissue ablation was reversed. Thus. mosquitoes were ovariectomized and later allatectomized (or overlying pleura perforated). Implanted postapolytic pupal ovaries generally developed, even though the corpora allata had been removed or overlying pleura perforated one
Inhibitory
regulation
day before implantation (Table 2). Indeed, JHstimulated, previtellogenic ovaries inhibited JH activity, demonstrating that development to the previtellogenic stage of ovarian arrest required the presence of corpora allata for at least 1 day following ovariectomy. Implanted pupal ovaries did not develop when corpora allata were removed before ovariectomy. and this established the ovary-corpus allatum stimulalory sequence. Finally. we determined whether implanted pupal ovaries develop in response to JH. Postapolytic pupal ovaries were implanted into adult mosquitoes; 1 day later, a JH analog or acetone solvent was applied. Of 12 such mosquitoes treated with analog, implanted ovaries developed in 75”,,. In contrast, ovaries developed in only 7”,, of 14 mosquitoes treated with solvent alone. This contirmed that JH stimulates ovarian development to the previtellogenic stage of arrest.
of mosquito CA
653
elaborate hormones that control the corpora allata (STAY et al., 1980), and our observations indicate that mosquito ovaries may function similarly. The ecdysteroids may fill such a function since they reportedly inhibit previtellogenic growth in newlyemerged mosquitoes (HAGEWRN er al.. 1977). Indeed, 20-hydroxyecdysone-induced germarium activity (BECKEMEYER and LEA, 1980) ceases and maximum titres of measurable hormone (HAGEDORN ef al., 1975) decline before JH activity is evident (FEINSOD and SPIELMAN, 1980a). Inhibitory control of the corpora allata by the ovaries appears to be an adaptation preventing premature development of ovarian follicles. Thus, less mature follicles would not develop to a vitellogeniccompetent stage until the most mature follicles were well advanced. Another ovarian hormonal process in mosquitoes is suggested by our observation that ovaries from preapolytic pupae cause degeneration of ovaries in previtellogenic arrest. The function of this effect is obscure.
DISCUSSION The corpora allata of mosquitoes appear to secrete periodically. JH activity is manifest within the first day after adult ecdysis (GWADZ and SPIELMAN, 1973) as well as 2 days after blood-feeding (FEINSOD and SPIELMAN, 1980a). Presumably this hormonal activity reflects secretory events that are regulated by specific physiological processes. The corpora allata of other adult insects appear to be regulated in part by inhibition, and these include cockroaches (STAY et al., 1980). and kissing bugs (PRATT and DAVEY, 1972). Our finding of the regulation of inhibition implies that the corpora allata of adult mosquitoes are inherently active. Ovarian tissues seem to regulate corpus allatum activity in adult cockroaches (STAY ef al.. 1980). Initial reports suggested that ovarian inhibition regulates JH in the kissing bug Rho&us prolixus (HUEBNER and DAVEY, lY73), but recent studies demonstrate that particular abdominal neurosecretory organs are responsible (DAVEY and KUSTER, 198 1). These organs frequently remain attached to associated tracheation of excised ovaries and have confounded earlier studies on these insects. Abdominal stretch, associated with blood-feeding, seems to be peculiarly important in regulating JH activity in bugs (WIGGLESWORTH,1934), and these organs may represent a special adaptation. We have compared the volume of tracheation remaining attached to excised ovaries of R. pro/&s and of A. aegypti (unpublished) and noted marked differences in this regard. We believe that this tracheation would not dislodge tissue attached to the abdominal wall of mosquitoes. Our observations suggest that tissues located within the ovarian envelope inhibit corpus allatum activity. Ovarian regulation of various developmental processes is generally humoral, and at least 1 ovarian hormone of mosquitoes has been demonstrated ( MEOI.A and LEA, 1972). Advanced vitellogenic ovaries prevent vitellogenesis in less advanced ovaries, apparently through humoral inhibition. But, because vitellogenesis is independent of JH, this ovarian hormone would not regulate corpus allatum activity. On the other hand. ovaries of cockroaches may
Acknow~ird~rmer~is-This study was supported by a contract DAMD 17-7X-C-8036 from the L!.S. Army Medical Research and Development Command. and by the Medical Research Council of Canada.
REFERENCES AI)AMS T. S. (1970) Ovarian
regulation of the corpus allatum
in the housefly. Mum dwwsri~cr.J. /~I.Yw~ P/~,Kw/.16, 349-360. ADAMST. S.. HINTZ A. M., and POMONIS J. G.. (1968) Oostatic hormone production in houseflies, Musca domrsricu. with developing ovaries. J. I~SKI Phvsiol. 14, 983-993. ANDERSON A. W. and SPIELMAN A. (1971) Permeability ofthe ovarian follicle of .4rdrs aeg.vp/i mosquitoes. J. Co// Biol. 50, 201-221. BECKEMEYEKE. F. and LtA A. 0. (1980) Induction of follicle separation in the mosquito by physiological amounts of ecdysterone. Scirnce. N. Y. 209, 819-821. DAVFY K. G. and KUSTER J. E. (1981). The source of an antigonadotropm in the female of Rhodtliu proliws Stil. (‘WI.J. Zoo/. 59, 76 l-764. FEINSOD F. M. and SPIELMAN A. (IYXOa) Independently regulated juvenile hormone activity and vitellogenesis in mosquitoes. J. Inswr Ph~~.siol. 26. 829-X32. FEINS~D F. M. and SPIELMAN A. (1980b) Nutrient-mediated juvenile hormone secretion in mosquitoes. J. frwc~f Phjxiol. 26, I I 3-l 17. GAKCIA M. L. M.. MELLC) R. P. and GAKUA E. S. (1970) Ecdysone. Juvenile hormone and odgensis in Rhucfnrrts proli.ws. J. In.sr~~~PhJ.tiol. 25, 695-700. GWAI)Z R. W. and SPltt.M.w A. (1973) Corpus allatum control of ovarian development in Arder aqypti. J. fnscvt Pltysiol. 19, 1441-1448. HAGEDOKN H. H.. O’CONNOK J. D. FUCHS M. S., SAGE B., SVHLA~GEK D. A. and BOHM M. K. (1975) The ovary as a source of z-ecdysone in an adult mosquito. Pr~x. wrn. .?tUC/. .%I. 1 ..s..1. 72. 3255-325Y. HAGEIXIKN H. H.. TVKN~K S.. HAGEDOKN E. A.. PoNt tc‘oav~ D.. GKtENHAt:M P.. PFEIEFEK D.. WtrEELO(‘h: G. and FLANAGAN T. R. (lY77) Postemergence growth of the ovarian follicles of .4rJe.~ uqvpri. J. Insrcr PI~~$o/. 23, 203-206. HIJE~NLK E.. and DALLY K. G. (1973) An antigonadotropin from the ovaries of the tnbect Rhodrriw pro/i.uus Stal. C’UI. J. Zoo/. 51. I 13-l 20.
LL:A A. 0. ( 1Y63) Some relationships between environment. corpora allata. and egg maturation in aedine mosquitoes. J. fnsrc~/ P/IWO/. 9, 79 3-809. 1.1.~ A. 0. ( 1969) Egg maturation in mosquitoesnot regulated by the C”rp”rd allata. J. Insuc,t Ph~sid. 15. 537-541.
I-IA
A. 0. f IY75) lzvidence that the ovaries of Mu.\ra ~lo~r~~\r~~udo not mamtam qchclt! b! regulatmg the corpus allaturn. J /SKI Plt~~srol. 21, 1747-l 750 Lt M P. T. M. I 1961) The reproductive system of some Florida mosquitoes. I ~-themale reproductive tract. Ann. (‘/If. SM. .4n1. 54, 397-401. M~OI.A R. and LEA A. 0. (1972) Humoral inhibition egg development in mosquitoes. J. wwd. Em. 9, 99-103. PAPPAS c. and FKAENK~L G. ( 1978) Hormonal aspecta of oiigenesis in the flies Phormiu rcyina and Sar~oplxqu
of
hulltitu. J. ln.~rc~/ Pi~yol. 24, 75-80. PR~I I G F :~ndD\\I 1 K (; (1’)711Thecorpusallatumantl oogene\lr 1n K~ICM/U,M\/JI~/I 11, Distal). I. The effects ol dllatectom\. J. E.vp.fhd 56, XI-2 14. SPIH,MAN A. and WONG J. (lY74) Dietar! laclor\ stimulating oiigensis in .4rdrs ur,qvpti. Bid. Bull. 147, 433442. SIAY B.. FKIEIXL T.. TOBE S. S. and Mtxaat_ E. <‘ (IYXO) Feedhack control of juvenile hormone s!nthcsis in cockroaches: possible role thr ecdysone. S~~~rnc~c, Y Y. 207. XYX-900 WIC~C~L.ESWOHTIH V. B. (lY34) The physiology of ecdysis m Rhoclnius pro/i.\-us (Hemiptera). II. Factors controlling moultmg and ‘metamorphosis’. Q. n~,c.rr,.\~ SC;. 77, IYI-222.
INHIBITORY
1981
0022-t 7Y0.8 I I0065 1_94$02.(Jl).(~ ( I YX I PrySlrnrl~ll PII,.\.\ Lrr/.
REGULATION OF CORPUS ACTIVITY IN MOSQLJITOES
ALLATUM
P. A. ROSSIGNOL, F. M. FEINSOD* and A. SPIELMAN Department
of Tropical
Public Health, Harvard School of Public Health. Boston. MA. 02 I 15. U.S.A.
665 Huntington
Avenue.
Abstract In order to determine whether juvenile hormone (JHt in mosquitoes is regulated by ovarran inhibitory feedback. we implanted JH-sensitive pupal ovaries into aJult mosquitoes and observed subsequent ovarian maturation. Removal or destruction of resting-stage ovaries (previously JH-stimulated) resulted in J H-stimulated development of implanted pupal ovartes. Ablation experiments demonstrated the ovary-corpus allatum sequence of maturation, and application of exogenoushormone analogs contirmed that development of implanted pupal ovaries is JH-dependent. Inctdental observations indicated that ovaries of preapolytic pupae produce a hormone that causes more mature ovaries to degenerate. We concluded that corpus allatum activity in Ardes aqqpri is regulated hy ovarian feedback inhibition. K(j), UOid bzde.~: Juvenile hormone. mosquitoes. reproductron. corpus allaturn. ovartes
INTRODUCTION factors regulate juvenile hormone (JH) in insects as diverse as cockroaches, bugs and flies. JH synthesis is reduced in a cockroach through an ovarian feedback mechanism apparently involving 20-hydroxyecdysone (STAYet al.. 198OJ, and the same hormone may behave similarly in a kissing bug (GAKCIA it al.. 1979). In addition, the corpora allata regulate previtellogenic development of the housetly and their activity is suppressed by an oostatic hormone deriving from vitellogenic ovaries (ADAMS et al., 1968: ADAMS. 1970). But, this interpretation is controversial (LEA. 1975; PAPPAS and FRAENKEL, 1978). Eggs of mosquitoes are produced in synchronous clutches. each stimulated by a meal of blood which induces the most mature follicles to develop synchronously, while less mature follicles await the next maturational stimulus. At least two hormonal complex pattern of coordinate this signals development. Follicles becomecompetent to sequester vitellogenin following stimulation by JH (ANDERSON and SP~LMAN, 1971; G$ADZ and SPIELMAN, 19731, but do not develop further until the mosquito takes a meal of blood. Thereafter. eggs mature independently of JH-stimulation (LEA. 1969). Two days after each meal of blood, JH stimulates the most mature follicles to become competent to sequester vitellogenin (FEINSOD and SPIELMAN, 1980a). Normally only the most mature follicle within each ovariole undergoes and this presents a problem of vitellogenesis, non-regulated coordinating JH-regulated and maturation. A meal of blood. through hormone-stimulatory mechanisms. coordinates vitellogenic development but the coordinating mechanisms for JH-regulated INHIBITORY
secretion
* Present address: Cleveland Metropolitan General Hospital. Department of Internal Medicine. 33Y5 Scranton Road. Cleveland. OH 44109. USA. 651
development is unknown. The simplest model requires that an ovarian hormone regulates allatum activity through feedback inhibition. Accordingly. we determined whether JH-stimulated ovary or ovaryassociated tissues affect JH activity. In addition. we examined the converse hypothesis that such tissues. not exposed to juvenile hormone. may stimulate JH activity.
MATERIALS
AND METHODS
At&s uqypri mosquitoes (Bahama strain) were used throughout this work. Origin of the strain, rearing procedures. and techniques for recording ovarian development have been described ( FEKLCOII and SPIELMAL 19XOb). At the beginning of each experiment. adult mosquitoes were 34 days postecdysis and non-mated. LCIM’S(1961) saline was the medium used for dissection as well as implantation. Mosqutloes were allatrctomt~ed as descrtbecl 1~) LEA (1963). In order to oppress the ovary against the abdominal wall. mosquitoes, otherwise provided with raisins. were permitted to gorge on IO”,, sucrose. Mosquitoes w’ere restrained in a piston device (SPIELMANand WONG. 1973). A lateral incision m the pleural membrane between the 7th and 8th abciominal segments was made using tinely honed forceps. The underlying ovary was grasped and gently drawn caudally. thereby breaking the common oviduct and permitting both ovaries to be withdrawn through one incision. A JH-analog (Altosid; Zoecon. Palo Alto. CA) wlas applied topically X0 ng in 0.X /iI 01‘ acetone/mosquito. Our JH-bioassay used ovaries removed from pupae. The presence of scales on the pharate adult was used to distinguish postapolytic from preapolyttc pupae. Ovaries were injected via a tapered capillary tube into thoraces of adult mosquitoes restrained in the piston device. In order to prevent excised ovaries from
P. A.
ROSSIGNOL, F.
M.
FEINSOD AND A. SPIELMAN
Table I. Development ofovariesremoved from pre- or postapolytic pupae and implanted into udult. lmale mczsqultoes with ovaries rcmovcd OI-with overlying pleura perforated Developmental stage of PUpa donating
I ength of follicles in freatment
ovarian impktnl
Implanted
)
IN0
ovaries
(“,, 2 70 jm~) (“,, degenerated)
perforaled
?(I 72
7.5 IX
Okaries removed
I2 ‘0
X? 711
Ovaries removed
LO
60
!I,
15
Plellr2
Pleura
resident ov3rIc:,
55 5
perforared
sticking to the walls of capillary tubes, albumin was added to the saline solution. later. implanted ovaries were removed measured using an ocular micrometer.
I”,, bovine Four days and then
RESULTS In a preliminary experiment, we determined whether ovaries, not yet stimulated by JH, may induce JH production. Since JH activity is detectable soon after adult ecdysis (GWADZ and SPIELMAN, 1973), we reasoned that pre-ecdysial pupal ovaries should be maximally stimulatory as well as responsive to JH. Accordingly, using apolysis as an additional preecdysial marker, we transplanted ovaries from pre-and postapolytic pupae into non blood-fed mosquitoes. II such treatment stimulated JH secretion, transplanted ovaries would develop to the previtellogenic stage ol arrest. Surprisingly, implanted postapolytic ovaries generally failed to develop, while those from preapolytic pupae developed to the previtellogenic stage of arrest (Table Ii. We noted that ovaries native to host mosquitoes more commonly degenerated in the presence of preapolytic pupal ovaries. In cases of extreme degeneracy. ovaries were composed largely of oviduct and trachioles: follicular tissue was not apparent. It may be that this functional ovariectomq promoted development of implanted ovaries by removing inhibitory factors. This finding led us to determine whether loss of ovarian could explain why implanted tissue
preapolytic pupal ovaries developed further than do postapolytic ovaries. Mosquitoes were ovariectomized and, 1 day later, pupal ovaries were implanted. Virtually all such pre- as well as postapolytic pupal ovaries developed to the previtellogenic stage of arrest (Table I), and this indicated that removal of JHstimulated ovaries may stimulate subsequent JH production. We then compared development of postapolytic pupal ovaries in ovary-intact vs ovariectomized mosquitoes. In this manner, we confirmed that ovariectomy promotes development of implanted pupal ovaries (Table II. Taken further, these experiments indicate that JH activity is not stimulated by JH-deprived ovaries. We tested the alternative hypothesis that ovaries in the previtellogenic stage of arrest may inhibit JH activity. In one experiment. mosquitoes were allatectomized and. I day later. ovariectomized. The following day, postapolytic pupal ovaries were implanted. Such implanted ovaries generally failed to develop, while similar ovaries implanted into ovariectomized mosquitoes having intact corpora allata (or overlying pleura perforated) developed to the previtellogenic stage of arrest (Table 2). In this experiment. allatectomy followed ovariectomy. In a companion experiment. the order of tissue ablation was reversed. Thus. mosquitoes were ovariectomized and later allatectomized (or overlying pleura perforated). Implanted postapolytic pupal ovaries generally developed, even though the corpora allata had been removed or overlying pleura perforated one
Inhibitory
regulation
day before implantation (Table 2). Indeed, JHstimulated, previtellogenic ovaries inhibited JH activity, demonstrating that development to the previtellogenic stage of ovarian arrest required the presence of corpora allata for at least 1 day following ovariectomy. Implanted pupal ovaries did not develop when corpora allata were removed before ovariectomy. and this established the ovary-corpus allatum stimulalory sequence. Finally. we determined whether implanted pupal ovaries develop in response to JH. Postapolytic pupal ovaries were implanted into adult mosquitoes; 1 day later, a JH analog or acetone solvent was applied. Of 12 such mosquitoes treated with analog, implanted ovaries developed in 75”,,. In contrast, ovaries developed in only 7”,, of 14 mosquitoes treated with solvent alone. This contirmed that JH stimulates ovarian development to the previtellogenic stage of arrest.
of mosquito CA
653
elaborate hormones that control the corpora allata (STAY et al., 1980), and our observations indicate that mosquito ovaries may function similarly. The ecdysteroids may fill such a function since they reportedly inhibit previtellogenic growth in newlyemerged mosquitoes (HAGEWRN er al.. 1977). Indeed, 20-hydroxyecdysone-induced germarium activity (BECKEMEYER and LEA, 1980) ceases and maximum titres of measurable hormone (HAGEDORN ef al., 1975) decline before JH activity is evident (FEINSOD and SPIELMAN, 1980a). Inhibitory control of the corpora allata by the ovaries appears to be an adaptation preventing premature development of ovarian follicles. Thus, less mature follicles would not develop to a vitellogeniccompetent stage until the most mature follicles were well advanced. Another ovarian hormonal process in mosquitoes is suggested by our observation that ovaries from preapolytic pupae cause degeneration of ovaries in previtellogenic arrest. The function of this effect is obscure.
DISCUSSION The corpora allata of mosquitoes appear to secrete periodically. JH activity is manifest within the first day after adult ecdysis (GWADZ and SPIELMAN, 1973) as well as 2 days after blood-feeding (FEINSOD and SPIELMAN, 1980a). Presumably this hormonal activity reflects secretory events that are regulated by specific physiological processes. The corpora allata of other adult insects appear to be regulated in part by inhibition, and these include cockroaches (STAY et al., 1980). and kissing bugs (PRATT and DAVEY, 1972). Our finding of the regulation of inhibition implies that the corpora allata of adult mosquitoes are inherently active. Ovarian tissues seem to regulate corpus allatum activity in adult cockroaches (STAY ef al.. 1980). Initial reports suggested that ovarian inhibition regulates JH in the kissing bug Rho&us prolixus (HUEBNER and DAVEY, lY73), but recent studies demonstrate that particular abdominal neurosecretory organs are responsible (DAVEY and KUSTER, 198 1). These organs frequently remain attached to associated tracheation of excised ovaries and have confounded earlier studies on these insects. Abdominal stretch, associated with blood-feeding, seems to be peculiarly important in regulating JH activity in bugs (WIGGLESWORTH,1934), and these organs may represent a special adaptation. We have compared the volume of tracheation remaining attached to excised ovaries of R. pro/&s and of A. aegypti (unpublished) and noted marked differences in this regard. We believe that this tracheation would not dislodge tissue attached to the abdominal wall of mosquitoes. Our observations suggest that tissues located within the ovarian envelope inhibit corpus allatum activity. Ovarian regulation of various developmental processes is generally humoral, and at least 1 ovarian hormone of mosquitoes has been demonstrated ( MEOI.A and LEA, 1972). Advanced vitellogenic ovaries prevent vitellogenesis in less advanced ovaries, apparently through humoral inhibition. But, because vitellogenesis is independent of JH, this ovarian hormone would not regulate corpus allatum activity. On the other hand. ovaries of cockroaches may
Acknow~ird~rmer~is-This study was supported by a contract DAMD 17-7X-C-8036 from the L!.S. Army Medical Research and Development Command. and by the Medical Research Council of Canada.
REFERENCES AI)AMS T. S. (1970) Ovarian
regulation of the corpus allatum
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