Effect of Temperature on the Life History of Cirrospilus sp. near lyncus (Hymenoptera: Eulophidae), a Parasitoid of Phyllocnistis citrella (Lepidoptera: Gracillariidae)

The effect of four constant temperatures on the life history of Cirrospilus sp. near lyncus was examined in the laboratory. This species is one of the most abundant generalist indigenous parasitoids of the citrus leafminer, Phyllocnistis citrella Stainton, in Spain. Adult lifespan of C. sp. near lyncus decreased from 50.2 to 9.1 days as temperatures increased from 15 to 30°C, respectively. Both gross fecundity and host-feeding were highest at 20°C (170.48 eggs and 32.33 hosts). Oviposition rates were optimal at higher temperatures (5.22 eggs per day at 25°C and 4.79 eggs per day at 30°C) and were dependent on female age. In contrast, host-feeding rates for a given temperature did not depend on age. Generation time decreased with increasing temperatures from 68.05 days at 15°C to 12.19 days at 30°C. Net reproduction peaked at 20°C (68.86 viable females per female). Intrinsic rate of increase doubled from 15°C (0.059 females per female per day) to 20°C (0.127 females per female per day) and almost doubled again from 20 to 30°C (0.210 females per female per day). Given these parameters, C. sp. near lyncus could perform optimally in the area occupied by P. citrella in the Mediterranean region.     

Reproductive biology of Fopius ceratitivorus (Hymenoptera: Braconidae), an egg–larval parasitoid of the Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae)

The reproductive biology of Fopius ceratitivorus Wharton, a recently discovered African parasitoid, was studied in quarantine in Hawaii to facilitate its mass production for biological control of the Mediterranean fruit fly, Ceratitis capitata. Mean longevity of host-deprived and ovipositing females was 17.3 ± 0.9 d and 16.2 ± 0.5 d, respectively. Ovarian maturation peaked at 61.6 mature eggs per female on the fifth day after eclosion and declined thereafter. Mean number of offspring produced per day by mated females was 5.1 ± 0.4, and realized fecundity expressed as total eggs deposited during the female’s life time was 107.8 ± 12.8. Females were more attracted, to and reproduced significantly more, in fruit substrates containing odors of adult flies and eggs rather than fruit substrates artificially inoculated with fly eggs. Our findings suggest that F. ceratitivorus is a promising new parasitoid for biological control of C. capitata in Hawaii.     

Measurement of vitellogenin,a biomarker for exposure to oestrogenic chemicals,in a wide variety of cyprinid fish

There is increasing concern about man-made chemicals in the aquatic environment that mimic oestrogens because they may disrupt reproductive function. Vitellogenin, a precursor of egg-yolk in fish and other oviparous animals, may be used as a biomarker for “oestrogen” exposure. This study investigated the use of a radioimmunoassay developed to carp (Cyprinus carpio) vitellogenin to measure vitellogenin in other species of fish, especially cyprinids that would be of value for field and laboratory studies on oestrogenic xenobiotics. Of the nine families of fish studied, only vitellogenin from cyprinids (to which the carp belongs) showed good cross-reactivity in the carp vitellogenin radioimmunoassay. Vitellogenin from cyprinids native to Europe that cross reacted in the carp vitellogenin radioimmunoassay included: bream (Abramis brama), roach (Rutilus rutilus), rudd (Scardinius erythropthalmus), gudgeon (Gobio gobio) and minnow (Phoxinus phoxinus). Vitellogenin from cyprinids used widely in ecotoxicology that cross reacted in the carp vitellogenin radioimmunoassay included: fathead minnow (Pimephales promelas), zebrafish (Brachydanio rerio) and goldfish (Carassius auratus). In the cyprinids studies, the concentrations of vitellogenin in mature females were between a few hundred and a thousand microgram per millilitre. Concentrations of plasma vitellogenin in immature females were always greater than 200 ng·m^-1, whereas in males (with the exception of the fathead minnow) plasma vitellogenin concentrations were less than 20 ng·ml^-1 (and generally, much lower). The results suggest that the structure of vitellogenin is highly conserved within the cyprinid family and that the carp vitellogenin radioimmunoassay may be used to measure the concentrations of vitellogenin in plasma from a wide variety of cyprinids.     

Development of Encarsia bimaculata (Heraty and Polaszek) (Hymenoptera: Aphelinidae) in Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) nymphs

Encarsia bimaculata was recently described from India as a potentially useful parasitoid of Bemisia tabaci. Its developmental biology was studied in the laboratory at 25–30 °C and 70–75% RH. Results showed that E. bimaculata is a solitary, arrhenotokous, heteronomous, autoparasitoid. Mated females laid eggs internally in B. tabaci nymphs that developed as primary parasitoids. Males developed as hyperparasitoids, either in females of their own species or in other primary aphelinid parasitoids. Superparasitism was common under cage conditions. Both sexes have an egg, three larval instars, prepupal, and pupal stages. Development from egg to adult took 12.70 ± 2.10 days for females and 14.48 ± 2.60 days for males. Individual B. tabaci nymphs were examined for E. bimaculata parasitization using three isozymes: esterase, malate dehydrogenase, and xanthine dehydrogenase. All three isozymes showed differential banding patterns that identified E. bimaculata parasitized or unparasitized B. tabaci nymphs.     

Age and sex dependence of the effects of an aqueous extract of Physalis alkekengi fruits on rat hepatic glucose 6-P dehydrogenase activity

Intraperitoneal injections of an aqueous extract of winter cherry fruits (Physalis alkekengi) to new-born, weanling and adult female rats and to weanling and adult male rats had no effect on body weight, liver weight and liver cytosol protein content. The specific activities of hepatic glucose 6-P dehydrogenase (an estrogen induced protein) in rats of different age and sex groups in terms of mU/mg protein were: treated new-born females, 15.9 ± 0.5; control, 29.1 ± 0.6; treated weanling females, 14.9 ± 0.3; control, 24.8 ± 0.7; treated adult females, 25.7 ± 0.5; control, 26.1 ± 0.5; treated weanling males, 7.9 ± 0.2; control, 7.9 ± 0.1; treated adult males, 9.6 ± 0.4; and control, 9.7 ± 0.3. Treatment of new-born and weanling female rats with the extract resulted in 40–45% reduction in hepatic G6PD activity. However, treatment of adult females, and weanling and adult males produced no significant change in the activity of this enzyme. The data are discussed both in terms of the increase in the capacity of rodent liver to metabolize steroidal compounds with age and the presence of low levels of circulating estradiol necessary for enzyme induction in male rats.     

Molecular characterization and mRNA transcript profile of vitellogenin in Chinese shrimp, Fenneropenaeus chinensis

A full-length cDNA encoding vitellogenin (Vg) was cloned from Chinese shrimp, Fenneropenaeus chinensis using RACE method. The full-length cDNA consist of 7,942 nucleotides including a 7,761 bp open reading frame, which encodes 2,587 amino acid residues. The deduced amino acid sequence showed high (from 94% to 37%) identity with other known crustacean Vgs. In addition, a consensus cleavage site (R-X-K/R-R) recognized by an endopeptidase and a member of subtilisin family of serine protease were identified in the deduced Vg precursor. RT-PCR analysis shown that Vg mRNA can be detected in both ovary and hepatopancreas of vitellogenic females but not in other experimental tissues including muscle, heart, lymph organ, gill, haemocytes and intestine. These results suggest that the Vg gene may be expressed exclusively in mature females, and both ovary and hepatopancreas are the possible tissues for Vg synthesis in F. chinensis. In addition, Vg gene is detected in genomic DNA of both females and males.     

Population and reproductive biology of the fiddler crab Uca thayeri Rathbun, 1900 (Crustacea: Ocypodidae) in a tropical mangrove from Northeast Brazil

Population and reproductive biology of Uca thayeri Rathbun, 1900 were studied for the first time in a tropical mangrove. Absolute density, sex ratio, population structure, handedness, breeding season and fecundity were investigated. Seven transects were delimited in a mangrove area of the Pacoti River, Northeast of Brazil (3° 43′ 02″ S/38° 32′ 35″ W). On each transect, ten 0.25 m² squares were sampled on a monthly basis during low tide periods from September 2003 to August 2004. A total of 483 crabs were obtained, of which 250 were males, 219 non-ovigerous females, and 14 ovigerous females. The U. thayeri population presented bi-modal size frequency distribution, with males and non-ovigerous females not differing significantly size-wise. Ovigerous females were larger than males and non-ovigerous females. The overall sex ratio (1:1.07) did not differ significantly from the expected 1:1 proportion. The major cheliped was the right one in 50% of the males. The observed density was of 8.5 individuals/m², with the specimens being found mostly in shaded areas. Ovigerous females were found in 5 months of the year, coinciding with the rainy season, suggesting that the population of U. thayeri presents seasonal reproductive events. Juvenile crabs were more abundant during the dry period, while larger crabs were found mainly during the rainy period. The fecundity of the studied population was much smaller than that of subtropical populations of this species. The regression analysis shows that the number of eggs increases linearly with the increase of carapace width.     

Evaluation of entomopathogenic nematodes against the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae)

Infectivity of six entomopathogenic nematode (EPNs) species against Bactrocera oleae was compared. Similar infection levels were observed when third-instar larvae were exposed to infective juveniles (IJs) on a sand-potting soil substrate. When IJs were sprayed over naturally infested fallen olives, many larvae died within treated olives as well as in the soil; Steinernema feltiae caused the highest overall mortality of 67.9%. In addition, three laboratory experiments were conducted to optimize a time period for S. feltiae field application. (1) Abundance of fly larvae inside fallen olives was estimated over the 2006–2007 season with the highest number of susceptible larvae (3 mm and larger) per 100 olives being observed during December, 2006. (2) S. feltiae efficacy against fly larvae dropped to the soil post-IJ-application was determined. B. oleae added to the substrate before and after nematode application were infected at similar levels. (3) Effect of three temperature regimes (min–max: 10–27, 6–18, and 3–12 °C) corresponding to October through December in Davis, California on S. feltiae survival and infectivity was determined. After 8 weeks, the IJs at the 3–12 °C treatment showed the highest survival rate. However, the cold temperature significantly limited S. feltiae infectivity. Our results demonstrate that B. oleae mature larvae are susceptible to EPN infection both in the soil and within infested olives. Being the most effective species, S. feltiae may have the potential to suppress overwintering populations of B. oleae. We suggest that November is the optimal time for S. feltiae field application in Northern California.     

Oviposition and reproductive performance of a generalist parasitoid (Trichogramma pretiosum) exposed to host species that differ in their physical characteristics

The response of generalist egg parasitoids to alternative natural hosts that are present simultaneously is not well known. We investigated the behavior of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) in relation to two field hosts Helicoverpa armigera Hübner and Spodoptera litura Fabricius, in choice and no choice tests. We quantified the effects of natal host species and post-emergence adult age on the oviposition preference of the parasitoids. H. armigera eggs were consistently preferred over S. litura eggs, regardless of the natal host and adult age. When only S. litura eggs were available as hosts, they were parasitized at statistically similar rates to H. armigera eggs (average of 17 ± 2.7 vs. 13 ± 3.0, H. armigera to S. litura). The adult lifespan and lifetime fecundity of T. pretiosum were variable but were affected by natal host species and/or host species to which they were exposed. Mean lifespan and fecundity of parasitoids that had developed in H. armigera eggs and were exposed to H. armigera eggs for oviposition were 13.9 ± 1.8 days and 98.7 ± 11.0 adult offspring. By contrast, those that developed in S. litura eggs and were exposed to S. litura eggs for oviposition lived for 7 ± 0.9 days and produced 53.8 ± 8.0 adult offspring. The ovigeny index (OI) was significantly lower in the parasitoids exposed to H. armigera eggs than in those exposed to S. litura eggs, regardless of the natal host, indicating that H. armigera eggs sustain the adult parasitoids better than S. litura eggs. These results are used to predict parasitoid behavior in the field when both hosts are available.     

The timing of hibernation in Tasmanian echidnas: why do they do it when they do?

We investigated the patterns of hibernation and arousals in seven free-ranging echidnas Tachyglossus aculeatus setosus (two male, five female) in Tasmania using implanted temperature data loggers. All echidnas showed a ‘classical’ pattern of mammalian hibernation, with bouts of deep torpor interrupted by periodic arousals to euthermia (mean duration 1.04±0.05 (n=146). Torpor bout length increased as body temperature fell during the hibernation season, and became more variable as temperature rose again. Hibernation started in late summer (February 28±5 days, n=6) and males aroused just before the winter solstice (June 15±3 days, n=3), females that subsequently produced young aroused 40 days later (July 25±3, n=4) while females that did not produce young hibernated for a further two months (arousal Sept 27±5, n=7). We suggest that hibernation in Tasmanian echidnas can be divided into two phases, the first phase, marked by declining minimum body temperatures as ambient temperature falls, appears to be obligatory for all animals, while the second phase is ‘optional’ and is utilised to varying amounts by females. We suggest that early arousal and breeding is the favoured option for females in good condition, and that the ability to completely omit breeding in some years, and hibernate through to spring is an adaptation to an uncertain climate.     

Immunochemical identification and partial characterization of female-specific serum proteins in white-edged rockfish,Sebastes taczanowskii

Synopsis Female-specific serum proteins (FSSPs) in white-edged rockfish,Sebastes taczanowskii, were identified and partially characterized by immunochemical procedures. Two FSSPs, which clearly reacted with antiserum against egg proteins, were confirmed in the serum of mature females, and estrogen treatment induced similar FSSPs in the serum of mature males. Hence, the FSSPs were considered to be vitellogenin. The vitellogenin concentration in female fish was high during the vitellogenic period and low during gestation, parturition and the recovery period, indicating that vitellogenin is used only for yolk formation in the oocytes and not as a direct nutritional source for developing embryos during gestation. On the other hand, an FSSP (FS3), which was considered not to be vitellogenin, was also identified in the sera of mature females and males after estradiol-17β administration by using an antiserum (a-FS3) that removed the components of the male serum and egg extracts from the anti-mature female serum antiserum. Moreover, immunohistochemical observation with a-FS3 illustrated that FS3 was a major constituent of the ovarian fluid but not of vitellogenic oocytes. The cross-reactivities of these FSSPs among seven viviparous rockfishes demonstrated that vitellogenin existed in the sera of all rockfishes studied belonging to the generaSebastes andSebastiscus, whereas FS3 was not present in several species ofSebastes.     

Vitellogenin expression in the oilseed rape pest Meligethes aeneus

When investigating insecticide resistance of pest insects, for example, the pollen beetle Meligethes aeneus, it is relevant to differentiate toxicological and molecular genetic data between male and female specimens. A molecular sex determination method would allow resistance testing to be run without prior sorting of the samples. A one-step quantitative RT-PCR method for quantification of the yolk protein vitellogenin expression in the pollen beetle was established. The expression level of vitellogenin relative to tubulin was determined. Pollen beetles were tested at different time points during their development to determine if vitellogenin is a reliable molecular marker for detection of sexually mature females. The differentiation between females and males by relative expression of vitellogenin to tubulin is conditional regarding the life cycle. Sexually mature females and males could easily be distinguished, whereas immature specimens could not be seperated. Vitellogenin expression is a successful marker for identification of sexually mature pollen beetles. Females from the spring populations showed vitellogenin expression when the temperature was above 10.2°C. Further, detailed observations of vitellogenin throughout the spring indicated a strong relationship between daily temperatures and vitellogenin expression, which is an indicator of oviposition ability.     

Grouping and Inhibition of Oogenesis in Two Strains of Acanthoscelides obtectus Say (Coleoptera Bruchidae) of Different Geographical Origin-Specificity of This Inhibitory Effect

Summary

Reproduction of A. obtectus females originating from Rubona (Rwanda) was inhibited after grouping (2 females, or 1 male—1 female). Only a few females produced mature oocytes; vitellogenin was synthesized, released into the haemolymph, but not incorporated into the oocytes. When females produced mature oocytes, their ovarian production was lower than in isolated virgin females. After pairing of a male and a female, 38% of the females mated, but mating under these conditions did not stimulate oogenesis.

Oogenesis of females originating from Tours (France) was only slightly inhibited by the presence of males or females of the same origin. “France” males and females inhibited the reproduction of “Rwanda” females under grouping conditions. However, “France” females showed only a slight sensitivity to grouping with “Rwanda” bruchids. In the presence of Phaseolus vulgaris seeds, grouping had no effect and all females, whatever their origin, produced mature oocytes. Inhibition weis relatively specific as cohabitation with bruchids of other genera (Callosobruchus maculatus-Zabrotes subfasciatus) had no effect. Cohabitation with two species of the same genus (Acanthoscelides obvelatus—A. argilaceus) inhibited oogenesis of A. obtectus “Rwanda” strain. The significance of this regulation and its importance in the maintenance of populations in nature are also analyzed.     

Adaptive difference in daily timing of hatch in two locust species,Schistocerca gregaria and Locusta migratoria: The effects of thermocycles and phase polyphenism

This study examined the effects of temperature and phase polyphenism on egg hatching time in the desert locust, Schistocerca gregaria, and the migratory locust, Locusta migratoria. The two species exhibited differences and similarities in hatching behavior when exposed to different temperature conditions. In 12-h thermocycles of various temperatures, the S. gregaria eggs hatched during the cryoperiod (low temperature period), whereas L. migratoria eggs hatched during the thermoperiod (high temperature period). The eggs of both species hatched during the species-specific period of the thermoperiod in response to a temperature difference as small as 1 °C. Furthermore, the locusts adjusted hatching time to a new thermal environment that occurred shortly before the expected hatching time. In both species, the hatching of the eggs was synchronized to a specific time of the day, and two hatching peaks separated by approximately 1 day were observed at a constant temperature after the eggs were transferred from thermocycles 3 days before hatching. Eggs laid by gregarious females hatched earlier than those laid by solitarious females in S. gregaria but this difference was not observed in L. migratoria.     

Mate recognition in the Aphis fabae complex: daily rhythm of release and specificity of sex pheromones

The two subspecies of the host-alternating black bean aphid, Aphis fabae Scopoli, used in this study have different secondary host plants but reproduce sexually in autumn on the same host plant, spindle, Euonymus europaea L. In both Aphis fabae fabae Scopoli and A. f. solanella Theobald the percentage of adult mating females (oviparae) calling (releasing sex pheromone) each day increased with age up to day 8. During the course of a day the mating females of A. f. solanella called most actively early in the morning and then showed a gradual decrease in calling activity. In contrast, few A. f. fabae called early in the day and were most active around midday, after which the incidence of calling decreased slightly, with 50% still calling in the evening. In both taxa the activity of the males in the absence of mating females paralleled the calling activity of their respective females. In an olfactometer, males showed a marked preference for the sex pheromone released by conspecific females over that of the other subspecies and did not respond to the odour of spindle. Thus, as in the other species of aphids there are specific mate recognition systems in A. f. fabae and A. f. solanella, which are likely to reduce the incidence of hybridisation.     

Precocious Mexican fruit fly methoprene‐fed males inhibit female receptivity and perform sexually as mature males

The sterile insect technique (SIT) has been used successfully for the control of fruit flies. The efficiency of this technique can be significantly reduced when sterile released insects are exposed to adverse conditions and predators, as a great number of sterile insects die before reaching sexual maturity and thus fail to mate with wild females. Treatments with juvenile hormone (JH) analogues such as methoprene (M) significantly reduce the time to reach sexual maturity by sterile Anastrepha ludens (Loew) (Diptera: Tephritidae) males. In this study, we compared the sexual performance of non‐treated sexually mature males with young males that had been sexually accelerated with M. Furthermore, we compared the ability of M‐fed males in inhibiting female remating compared with sexually mature males. Results showed that at 5 days M‐fed males had lower mating success than mature males; however, 6‐day‐old (0.1%) M‐fed males had the same amount of matings as mature 13‐day‐old males. Young 5‐ to 10‐day‐old M‐fed males also had similar number of matings as mature non‐treated 12‐ to 17‐day‐old males. There were no differences in copula duration between treatments. Moreover, there were no differences between the fertility, fecundity or refractory period of females mated with either young male fed M or normal sexually mature males. These results indicated that young males that were sexually accelerated with M have the same sexual performance as non‐treated sexually mature males. Implications of using M as a pre‐release treatment for A. ludens controlled through SIT are discussed.     

Molecular Characterization of Japanese Sillago Vitellogenin and Changes in Its Expression Levels on Exposure to 17β-Estradiol and 4-<Emphasis Type="Italic">tert</Emphasis>-Octylphenol

We cloned a full-length cDNA encoding vitellogenin (VTG) from a marine teleost, the Japanese sillago Sillago japonica. The cloned sillago VTG contained signal peptide, lipovitellin heavy chain, phosvitin, lipovitellin light chain, and β′-component in the order from the N-terminus. An exposure to 17β-estradiol significantly increased the levels of plasma VTG, but not hepatic VTG mRNA in males. Neither plasma VTG nor hepatic VTG mRNA levels were affected by the exposure to 4-tert-octylphenol. Hepatic VTG mRNA levels in males increased at 1 day after intraperitoneal administration of 17β-estradiol but decreased in the subsequent 5 days. However, plasma VTG levels remained high for 5 days after administration, suggesting that the accumulation period of plasma VTG is longer than that of hepatic VTG mRNA in males. Therefore, VTG mRNA may be a suitable indicator of temporal exposure to estrogenic chemicals in the environment, whereas plasma VTG is useful to detect consecutive exposure.     

Changes in various plasma lipid components, glucose, and insulin in Spermophilus lateralis during hibernation

This study evaluated fat mobilization as related to gluconeogenesis in two age groups of hibernating golden-mantled ground squirrels (Spermophilus lateralis). Our experimental group consisted of a total of 16 male and 15 female squirrels. Plasma samples were collected from selected animals being killed weekly from January to March, and the concentration of triglycerides, glycerol (GY), free fatty acids (FFA), total cholesterol, lipase activity, glucose, and insulin, were determined by biochemical assays and radioimmunoassay. Our results showed a mean FFA/GY ratio of five, which was higher than the predicted value of three, suggesting a significant depletion of GY and an enhanced rate of gluconeogenesis via GY to maintain glucose homeostasis in the hibernating animals. The factor of age did not significantly affect plasma lipid components. However, in the male group, plasma glucose levels were significantly higher for adults than for juveniles. Overall, females had significantly higher plasma glucose levels than males (150 ± 11 vs. 110 ± 8 mg%, P < 0.05). In the adult group, a gender influence was also seen on plasma insulin levels, with females' being higher than males' (66 ± 13 vs. 25 ± 3 μIU/ml, P < 0.01). We suggest that during hibernation, female squirrels may have a higher rate of lipolysis and gluconeogenesis along with a lower glucose utilization than their male counterparts. Additionally, adult females may exhibit a higher peripheral insulin resistance during hibernation than adult males, a possibility which merits further study.     

Behavioral and reproductive responses of female opossums to volatile and nonvolatile components of male suprasternal gland secretion

Female gray short-tailed opossums (Monodelphis domestica) lack an estrous cycle and are induced into estrus by exposure to a pheromone in male scent marks. Behavioral and physiological responses of females to the volatile and nonvolatile components of scent marks were examined in two experiments. Young females (n = 9) were tested prior to and during their first estrus for behavioral responses to scent marks, collected on a 7-ml glass vial rubbed over the suprasternal gland of a mature male. The response to volatile components of the scent mark, recorded when marked and unmarked vials were covered with a perforated shield, was compared to the response to these vials when unshielded. Estrous females nuzzled the shields over marked vials (55.8 ± 8.5 nuzzles/10 min) more than the shielded clean vial (10.9 ± 2.4) (P < 0.05); a similar response was observed in anestrous females. Nuzzling of unshielded, scent-marked vials was higher (P < 0.05) during anestrus than in the same females when in estrus. The role of nonvolatile pheromones in reproductive activation was tested in adult females (n = 11) exposed for up to 14 days to a shielded, marked vial or to an unshielded, marked vial in a crossover design. All females exposed to unshielded vials expressed estrus, and 10 copulated. Only 2 females expressed estrus (significantly fewer, P < 0.05), when exposed to shielded marked vials, and neither copulated. These results demonstrate that females detect and respond behaviorally to both volatile and nonvolatile components of male suprasternal gland secretion, but the estrus-inducing pheromone in these secretions is nonvolatile.     

Timing of female sexual unreceptivity and male adjustment of copulatory behaviour under competition risk in the wolf spider <Emphasis Type="Italic">Schizocosa malitiosa</Emphasis>

Males can change their copulatory or sperm transfer patterns in response to sperm competition risk. Schizocosa malitiosa performs long copulations, which include two consecutive patterns (Patterns 1 and 2). Virgin females are very sexually receptive, but mated females diminish their receptiveness. Female unreceptivity has been attributed to the action of receptivity-inhibiting substances, mainly transferred during Pattern 1. We tested: (1) if females who mated only with Pattern 1 were immediately unreceptive; (2) male and female behaviours when the copulating couple was exposed to another male. For (1), we interrupted mating when Pattern 1 finished and immediately exposed the female to a second male. For (2), we introduced a second male when the couple was starting (Ei) or finishing copulation (Li). Females were unreceptive immediately after finishing Pattern 1. Males from Ei and Li dismounted and approached the second males. Ei males diminished the frequencies of insertion after perceiving the presence of a second male and dismounted less frequently when copulating with heavy females. The study provides insights about the timing of sexual unreceptivity in S. malitiosa under possibilities of sperm competition, discussing male adjustment of copulatory behaviour in the presence of rival males. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.