Quantity of the male ejaculate influenced by female unreceptivity in the fly, Culicoides melleus

The number of sperm placed in the spermatophore by virgin Culicoides melleus males mated with virgin females was compared with the number deposited in matings with previously once or twice copulated females. When compared to an all-virgin mating, there was a significant reduction (P<0·001) in sperm complement (of 15 per cent) when the female had already been mated once as compared to a virgin, and a greater reduction (of 21 per cent) when the female had already been mated twice. The mean numbers (± S.E.) of sperm ejaculated with virgin, once mated, and twice mated females were 857 ± 24, 732 ± 23, and 673 ± 25, respectively.When a major activity in the unreceptive behaviour of females (kicking at the male in the early stages of copulation) was prevented by amputation of the hind legs, the mean number of sperm ejaculated (788 ± 29) was significantly larger (P<0·01) compared with twice mated females having both legs intact, and also larger, though not significantly so, than with intact once mated females. In addition to the kicking activity, there was evidence that other forms of unreceptive behaviour contributed to reducing the quantity of sperm ejaculated.     

Prostaglandins in the cabbage looper, Trichoplusia ni

Low levels of prostaglandin (PG)-like compounds were detected by radioimmunoassay in reproductive tissues of Trichoplusia ni adults. A 3-fold increase in PGE₂-equivalents was found in mated female reproductive tissues. A PGF_2x-like compound was found in reproductive tissue of mated females with a 2-fold increase over that in virgin females.Injected PGE₁, PGE₂ and PGF_2x had no effect on levels of Z-7 dodecenyl acetate (Z-7-12: Ac) in pheromone-producing glands or oviposition of virgin female T. ni. No significant in calling behaviour were observed in virgin females injected with prostaglandin when compared with control virgin females.N-acetyl-p-aminophenol (NAPAP), a prostaglandin-synthetase inhibitor, in the diet of adult females did not alter calling behaviour of virgin or mated females. NAPAP in the larval diet lengthened larval stadia and slightly increased calling by mated females, but did not reduce oviposition after mating. Levels of Z-7-12:Ac in pheromone-producing glands of virgin and mated females were not affected by NAPAP in diets of larvae or adults.     

Factors affecting pheromone secretion and oviposition by fertilized females of Culicoides nubeculosus (Diptera: Ceratopogonidae)

The effect of age and a blood meal on pheromone secretion by virgin and fertilized females of Culicoides nubeculosus was studied. In virgin females, the secretion varies in relation to age, the blood meal, and oviposition. In fertilized females, rate of pheromone secretion is very low after fertilization and does not seem to vary subsequently in relation to the above factors. Mating was found to accelerate oviposition. The role of seminal fluid in the decrease in rate of pheromone secretion by fertilized females is discussed.     

Prostaglandin and prostaglandin synthetase in the cricket, Acheta domesticus

Prostaglandin (PG) synthetase was present in the testes, seminal vesicles, and spermatophores of the male house cricket, Acheta domesticus. The enzyme was not detected in bursa copulatrix, spermatheca, spermathecal canal, and oviducts from virgin females, while substantial activity was measured in the same tissue from mated females. The female appears to receive the enzyme from the spermatophore. A PGE₂-like material was detected by radioimmunoassay in A. domesticus testes and to a lesser extent in the remainder of the male reproductive tract. PG went undetected in virgin female reproductive tissues, while the same tissues from mated females contained an average of 589 pg of PGE₂-like material per female. In in vivo studies, injected PGE₁, PGE₂, and to a smaller degree PGF_2α stimulated oviposition by virgin females. Moreover, N-acetyl-p-aminophenol, a PG synthetase inhibitor, suppressed oviposition in mated females. Post-copulatory PG biosynthesis in the female reproductive tract might be partially responsible for triggering oviposition in A. domesticus. Since PG synthetase appears to be acquired from the male, it could be considered a primer pheromone.     

The role of cuticular hydrocarbons in male attraction and repulsion by female Dawson's burrowing bee, Amegilla dawsoni

Cuticular hydrocarbons (CHCs) are long-chain fatty acids and their derivatives that protect insects from desiccation. They can also be important semiochemicals in insect reproduction. We used behavioural and chemical assays to examine the potential role of CHCs in sexual communication in a solitary burrowing bee, Amegilla dawsoni. Washing CHC blends from the cuticle of emerging virgin females made them unattractive to mate-searching males. Returning the CHC blends restored their attractiveness. Nesting females were unattractive to mate-searching males, whether they were washed or not. Chemical analysis identified significant differences between male and female CHC blends and between virgin female and nesting female blends. Some of these differences were due to specific compounds. Loss of attractiveness is unlikely to be due to antiaphrodisiac compounds delivered by males, because male-specific compounds were not found on nesting females, and because recently mated females with intact CHC blends were attractive to searching males. Nesting females could not be made attractive to searching males by removing their CHC blends. Adding virgin female CHC blends tended to improve attractiveness but the effect was weak, suggesting that some form of volatile compound may also be involved in signalling unreceptivity.     

The effects of mating,exogenous juvenile hormone and a juvenile hormone analogue on pheromone titre,calling and oviposition in the omnivorous leafroller moth (Platynota stultana)

Mating in Platynota stultana resulted in the termination of calling, the gradual reduction of pheromone in the pheromone glands to non-detectable levels (<0.1 ng/♀) within 14 h, and oviposition of the first batch of eggs 20–24 h after copulation. Decapitation of virgin females resulted in a similar decline in pheromone titre, and also eliminated oviposition and calling. Pheromone production appears to be controlled via the head. Mating probably terminates neural or hormonal input required for pheromone production and/or removes neural or hormonal inhibition of pheromone degradation. A juvenile hormone analogue (ZR-512) and juvenile hormones I, II and III applied exogenously to virgin females elicited oviposition comparable to mated females and terminated calling within 48 h. The juvenile hormone analogue also appeared to block pheromone production in virgin females. These results suggest that juvenile hormone may be involved in the switch from virgin to mated behaviour in this species.     

Courtship-stimulating volatile compounds from normal and mutant Drosophila

Volatile compounds from Drosophila melanogaster males and females dramatically affect male courtship behaviour. These substances, which have been extracted from flies of different ages and genotypes, have been analysed by gas chromatography (GC) and in behavioural assays. Extracts from virgin females and males have different gas chromatographic profiles, which may reflect the fact that extract from virgin females stimulates high levels of courtship between males over short distances, while extract from mature wild-type males does not affect sexual behaviour. However, volatile compounds from very young males or males expressing the fruitless (fru) mutation do stimulate courtship between males, and chromatographic profiles of young male and fru male extracts differ from the GC profile of extracts from mature wild-type males.     

Endocrine control of vitellogenesis in the harlequin bug, Dindymus versicolor

An active corpus allatum is essential for the maturation of eggs in the harlequin bug, Dindymus versicolor. The corpus allatum of virgin females remains virtually inactive and the oöcytes are resorbed once they have grown to the stage at which they become competent to incorporate yolk. Mating provides a stimulus which is essential for the initiation and maintenance of corpus allatum activity and, therefore, vitellogenesis. Corpus allatum activity (and vitellogenesis) can be induced in virgin females either by cutting the allatic nerves or by excision of a certain part of the protocerebrum. It is concluded that the corpus allatum of virgin females is inhibited nervously by the brain and that copulation provides a nervous stimulus which lifts this cerebral inhibition thereby permitting allatum activity.The median neurosecretory cells are not essential for vitellogenesis in Dindymus; however, it is suggested that they are necessary for maximum allatum activity. Evidence is provided to show that the growth and maintenance of the previtellogenic oöcytes are also under the control of the corpus allatum. A mechanism is described whereby the number of vitellogenic oöcytes in the ovarioles is maintained constant.     

Chemosensory cues allow male Tenebrio molitor beetles to assess the reproductive status of potential mates

Males of many insect species, including beetles, choose their mates according to their reproductive status. However, the ways in which male beetles evaluate female reproductive status have received little attention. We tested the existence of male mate choice in the mealworm beetle, Tenebrio molitor, by observing mating and courtship behaviour of males given simultaneous access to pairs of females differing in their reproductive status: (1) mature versus immature; (2) virgin versus previously mated; (3) familiar (mated with the experimental male) versus unfamiliar (mated with a different male). Males courted and mated preferentially with mature and virgin females. To determine whether chemical cues played a role in these discriminations, we exposed males to filter paper squares bearing chemical cues from different types of females: (1) virgin versus mated; (2) mature versus immature. Males were significantly more attracted to those squares bearing chemical cues from virgin and mature females, suggesting that males can assess female reproductive status on the basis of chemical cues alone.     

Acoustic courtship signals in the Caribbean fruit fly, Anastrepha suspensa (Loew)

Male Caribbean fruit flies, Anastrepha suspensa (Loew) produce two sounds in sexual contexts, calling songs and precopulatory songs. Calling song occurs during pheromone release from territories within leks and consists of repeated bursts of sound (pulse trains). Virgin female A. suspensa became more active in the presence of recorded calling songs. Activity during the broadcast of a heterospecific song did not differ from movement during periods of silence. A conspecific song typical of smaller males, i.e. conspicuous for its long periods between pulse trains, also failed to elicit more activity by virgin females than silence. Mated females were most active during silences. Unmated males had no obvious reaction to sound. Calling songs are apparently sexually important communications which females discriminate among and may use as cues for locating and/or choosing between mates. Precopulatory song is produced by mounted males just before and during the early stages of copulation. Males that did not produce such songs remained coupled for shorter periods, perhaps passing fewer sperm. Wingless (muted) males were more likely to complete aedeagal insertion if a recorded precopulatory song was broadcast. Calling song played at the same level (90 dB) had no significant effect on the acceptance of males, nor did precopulatory song at a lower SPL (52dB). Precopulatory song may be used to display male vigour to choosing females.     

The role of antennae in the thermopreference and biting response of haematophagous bugs

Insects sense thermal cues mainly through thermoreceptors located in the antenna. To analyse the impact of antennectomy on the thermal behaviour of the haematophagous bug Triatomainfestans, we studied the distribution of intact and antennectomised bugs in an experimental arena where a temperature gradient was established, as well as the biting response of insects with and without antennae to objects at the temperature of a potential host. Antennectomy did not abolish thermopreference, but modified the temperature at which the insects preferred to stay. In the arena, antennectomised insects chose to remain at a higher temperature (ca. 3 °C higher in unfed bugs), and exhibited a larger dispersion around that preferred temperature, than intact bugs. In addition, ablated insects temporarily lost their ability to bite an object at the temperature of a potential host, but that ability was gradually recovered after the fifth day post-antennectomy. Results presented here show that thermoreceptors other than those located on the antennae can also guide thermal behaviours. We conclude that the function of antennal thermoreceptors can be taken over by other receptors located in different regions of the body. Those receptors have a different sensitivity and confer the insects with a different responsiveness.     

Determination of the site of pheromone emission in the virgin females Culicoides nubeculosus Meigen (Diptera: Ceratopogonidae)

The zone of emission of the sex pheromone from the body of Culicoides nubeculosus was investigated. The amount of pheromone emitted was evaluated by counting the number of matings between males and females exposed to a flow of air coming from a chamber containing virgin females. The number of matings is higher than that recorded when the air flow comes from an empty chamber (control). Three parts of the body were examined: head, thorax and abdomen. Each part was studied by neutralizing the effect of the others. The head was neutralized by decapitation and the females continued to emit pheromone. The head is, therefore, not indispensible for pheromone emission. The roles of the thorax and abdomen were studied by coating these with paraffin wax. When the thorax is coated, pheromone emission continues, but when the abdomen is coated, it stops. It appears that the abdomen alone is responsible for emission of the sex pheromone.     

Male accessory gland substance of Melanoplus sanguinipes: An oviposition stimulant under the control of the corpus allatum

The accessory glands of male Melanoplus sanguinipes contain an oviposition stimulant. Injection of gland extracts from mature males induces oviposition in 75 per cent of capable virgin females within 24 hr. Injection of gland extracts from allatectomized males produces no stimulatory effect. Gland extracts from mature males contain two antigens which cannot be detected in gland extracts from allatectomized males. However, both antigens can be detected in gland extracts from allatectomized males 3 days after treatment with juvenile hormone.Anion-exchange chromatography of mature gland extracts yielded two fractions which, when injected into virgin females, induced oviposition in 71 per cent of capable insects within 24 hr. These two fractions are immunologically identical to the two antigens which are absent from gland extracts of allatectomized males. We suggest that synthesis of the oviposition stimulant in Melanoplus is controlled by the corpus allatum.Injection of brain extract also induces oviposition in 100 per cent of capable virgin females within 24 hr. A possible rôle for the brain in the oviposition process is discussed.     

The role of endocrines in flight-muscle degeneration in Dysdercus cingulatus (Heteroptera: Pyrrhocoridae)

In Dysdercus cingulatus, extirpation of the median neurosecretory cells inhibits flight-muscle breakdown. However, implantation of median neurosecretory cells or corpus allatum into females lacking these neurosecretory cells induces muscle histolysis. Median neurosecretory cells stimulate the corpus allatum to produce juvenile hormone which in turn induces muscle degeneration. Topical application of kinoprene induces muscle breakdown, even in males and starved virgin females. The direct participation of juvenile hormone in muscle degeneration is further confirmed by observations on the effect of precocene II which inhibits muscle histolysis in many individuals. The endocrine basis of vitellogenesis and flight-muscle degeneration could be identical; vitellogenesis however appears to require a higher threshold concentration of juvenile hormone.     

Age-dependent pattern of calling behavior in <Emphasis Type="Italic">Atheloca subrufella</Emphasis> (Hulst) (Lepidoptera: Phycitidae)

Changes in the signaling effort of virgin females are known to occur until their first mating. Young females tend to increase the calling effort (number and time duration of bouts) as they age. In this context, the calling behavior of virgin females of Atheloca subrufella, an important pest of coconut palms (Cocos nucifera), was studied under laboratory conditions. Thirty four virgin females were observed during 16 scotophases (25 ± 2 °C, 75 ± 5 % RH and 10 h scotophase), until they stopped calling in the following photophase. The calling position, pattern and frequency were evaluated. Females of A. subrufella showed only one calling position, and calling peaked between the second and fifth scotophases. Most females did not start calling immediately after emergence. Neither the individual duration of calling nor the number of calling bouts changed over time. However, the time that calling started was earlier in older females, probably to avoid competition with younger females and increase the probability of mating. These data support the hypothesis that there is an age-dependent pattern of pheromone emission in virgin females of A. subrufella.     

The behavioral and somatic effects of ovariectomy and replacement therapy in female collared lemmings (Dicrostonyx groenlandicus)

Reproductive behavior and organ weights in intact estrous and diestrous, and in ovariectomized treated and untreated female collared lemmings (Dicrostonyx groenlandicus) were examined. Sexual behavior of intact diestrous and untreated ovariectomized females was similar, and females in both groups behaved differently from intact estrous females in scores for lordosis and mounting the male. Receptivity was observed in some females within 3 days after the first daily dose of as little as 0.1 μg of estradiol benzoate (EB) and in 83% of all females treated with 0.1 μg or more of EB for 5 days. Vaginal perforation and cornification were related to the dose of EB and length of treatment. The doses of EB used were not related to the lordosis quotient. Ovariectomy and subsequent EB treatment influenced uterine but not preputial gland weight. Adrenal weight was not influenced by ovariectomy or EB treatment, but the increased adrenal weights observed may have been related to the daily pairing of females with males.     

Influence of diet on synthesis and utilisation of lipids for reproduction by the tsetse fly Glossina morsitans

Fatty acid composition of lipids from adult Glossina morsitans was unaffected by an in vitro fed diet of cow blood which induces production of under-sized offspring compared to that of flies fed on a superior diet of pig blood. The commonest fatty acids were C_16:0, C_16:1 and C_18:1 and only small differences in proportions were detected between virgin and pregnant females. Rate of lipid accumulation by males and females was the same and was unaffected by diet, but males achieved a maximum of 2.5 mg on day 9 while both virgin and fertilised females reached a maximum of 5,0 mg on day 14 of adult life. Lipid content of pregnant flies then fell to 3.0 mg on the day of larviposition and accumulation began again. A cow blood diet reduced the extent to which the lipids were utilised for larval growth and this was reflected in an altered secretory activity cycle in the female uterine gland. However, no effect on the growth of adult fat body was detectable in such flies. Mating and fertilisation, which influence reproductive events through activity of the endrocine system do not seem to affect the acquisition of lipid reserves by female Glossina. However, they clearly exert considerable influence over distribution of such reserves between fat body and uterine gland, which distribution is also affected by diet.     

Sex pheromones enable Drosophila males to discriminate between conspecific females from different laboratory stocks

Drosophila melanogaster males from Canton-S and Oregon-R stocks perform more courtship in response to virgin females from the stock other than their own. Pairs of Canton-S and Oregon-R males also court each other more in the presence of volatile compounds extracted from Oregon-R and Canton-S females, respectively. These observations suggest that D. melanogaster females are polymorphic with respect to some components of their sex pheromone system and that males are capable of distinguishing females from their own stock and females from another stock on the basis of these differences in pheromone production.     

The effects of visual social stimulation upon age at first spawning in the mouth-brooding cichlid fish Sarotherodon (Tilapia) mossambicus (Peters)

The effect of visual social stimulation upon age at first spawning of Sarotherodon (Tilapia) mossambicus was studied by rearing newly-released young in one of two conditions: isolated or in visual contact with a conspecific of the same age in an adjacent aquarium. Results indicated that isolation delayed first spawning by about 10 days for isolated females as compared to socially stimulated females. The rate of colour development was the same for all males suggesting that testicular maturation was not greatly affected by visual social stimulation. In addition, growth of social females lagged behind that of isolates. Some mechanisms and biological effects are discussed.     

The relationship of age,sex, and reproductive state to assimilation efficiency in the adult milkweed bug, Oncopeltus fasciatus

The influence of age, sex, and reproductive state on efficiency of assimilation was examined in the milkweed bug Oncopeltus fasciatus. Amounts of food ingested and excreted decline with age in virgin males and females. Mated females laying eggs ingest significantly more food than virgin animals of either sex and also maintain a consistently higher assimilation efficiency. A qualitative analysis of the level of assimilation required for reproductive effort is discussed.