Effets d'un régulateur de croissance d'insectes,le fénoxycarbe,sur la diapause du psylle du poirier Cacopsylla pyri

The nature of the responses of the sheep blowfly Lucilia sericata Meigen (Diptera: Calliphoridae) to carrion odours and carbon dioxide were examined in a windtunnel in the laboratory and the attractiveness of carrion-bait was examined in the field. In the wind tunnel, gravid 9-day-old females increased both the number and duration of their flights, in response to carrion odours. In addition, linear velocity was reduced and the sinuosity of flight increased in the presence of these odours. With 3-day-old females, the response to carrrion odour depended on previous exposure to proteinaceous material. Protein deprived females showed kinetic responses to carrionodour which were similar to those of gravid females. No such changes were observed in protein-fed females. No responses to CO₂ were observed. In the field, the importance of olfactory cues in bait location was demonstrated by the absence of L. sericata from sticky targets lacking an odour bait. Increased bait concentration did not affect the age, sex ratio or ratio of L. sericata to other Lucilia spp. caught, but did increase the numbers caught. Analysis of the reproductive status of females caught, indicated that a greater number of gravid females were caught than expected, while a lower number of females in the final stages of vitellogenesis were caught than expected. The results show that the responses of L. sericata to odours are complex, and are dependent on both exogenous and endogenous stimuli, the latter including the stage of ovarian development.     

Fitness consequences of alternative life histories in water striders,Aquarius remigis (Heteroptera: Gerridae)

Using field and laboratory observations and experiments over 3 years, I investigated whether reproductive trade-offs shape individual life histories in two natural populations of the water strider, Aquarius remigis, in which univoltine and bivoltine life cycles coexist. Both later eclosion dates and food shortages, even after adult eclosion, induced diapause in females, thus deferring reproduction to the following spring. Adult body size was positively affected by food availability during juvenile development. Higher food levels also increased the reproductive output of females, but not their longevity or oviposition period. When compared to spring breeders (univoltine life cycle), direct (summer) breeders (bivoltine life cycle) experienced reduced lifetime egg numbers and longevity, as well as reduced survivorship of their second-summer-generation offspring; these reproductive costs offset, at least in part, the advantage in non-decreasing populations of having two generations per year. Fecundity was correlated with body size, and among summer-generation females direct breeders were larger than non-breeders. The time remaining before the onset of winter and/or the time since adult eclosion augmented cumulative energy uptake, and consequently the lipid reserves and winter survival probability of non-breeding (diapausing) summer adults approaching hibernation. Overwintered spring reproductives died at faster rates than non-reproductive summer individuals despite greater food availability in spring, indicating a mortality cost of reproduction. Body length correlated with absolute and not with proportional lipid content but showed no consistent relationship with survivorship in the field. These results are in agreement with current theory on the evolution of insect voltinism patterns, and further indicate high degrees of life history flexibility (phenotypic plasticity) in the study populations in response to variable environmental factors (notably photoperiod and food availability). This may be related to their location in a geographic transition zone from uni- to bivoltine life cycles.     

Reproduction in captive lion tamarins (Leontopithecus): Seasonality,infant survival,and sex ratios

Diversity in reproductive and social systems characterizes the primate family Callitrichidae. This paper contributes to our appreciation of this diversity by presenting the first detailed comparative analysis of captive breeding in three species of lion tamarins (Leontopithecus chrysomelas, L. chrysopygus, and L. rosalia) housed at the Centro de Primatologia do Rio de Janeiro. The annual pattern of reproduction in all three species of Leontopithecus was markedly seasonal, with births occurring during the spring, summer, and fall months from August through March. While modal number of litters produced per female per year was 1, approximately 20% of breeding females produced two litters per year. The onset of breeding activity in years when two litters are produced was significantly earlier than in years when only one litter was produced. The cumulative number of offspring surviving to 3 months of age did not differ between years with one vs. two breeding attempts. Like other callitrichids, postnatal mortality was highest during the first week of life, and there were pronounced species differences in offspring survival through 1 year, with significantly lower survivorship in L. chrysomelas. Infant survivorship was affected by a number of experiential factors. Survivorship up to 30 days of life was higher in groups in which the breeding female had previous experience with infants as a nonbreeding helper than in groups in which the female lacked previous helping experience. Likewise, survivorship to 30 days of life was higher for infants born to multiparous females than for infants born to primiparous females. When parity and previous helping experience were analyzed concurrently, the lowest survivorship was associated with offspring produced by inexperienced primiparous females. Genus-wide, there was no significant departure from a 50:50 sex ratio at any point during the first year of life, nor was there evidence for differential mortality for male and female infants. However, L. chrysopygus produced significantly more male infants at birth (65:44) and had male-biased litters (approximately 60% males) throughout the first year of life, while L. chrysomelas showed a nonsignificant tendency toward female-biased litters. © 1996 Wiley-Liss, Inc.     

Adult mortality and oviposition rates in field and captive populations of the blowfly Lucilia sericata

Abstract.  1. Adult mortality and oviposition rates were determined for populations of the blowfly Lucilia sericata (Meigen) (Diptera: Calliphoridae). This species is of economic importance as the primary agent of sheep myiasis throughout north-western Europe.
2. Populations of marked flies in six, 1 m³, outdoor field cages and unmarked wild flies at two farms in south-west England were studied simultaneously between May and September 1998.
3. In the field, wild female L. sericata were caught and aged using a combination of wing-fray and ovarian dissection techniques. Survivorship analysis gave estimates of mortality of 1.94% (± 0.037) and 2.09% (± 0.044) per day-degree and mean life expectancy of 51.5 and 47.9 day-degrees above a threshold of 11 °C, at the two farms studied. Mean lifetime reproductive output in the field was estimated to be 159.6 and 138.4 eggs per female at the two farms respectively.
4. The survivorship of cohorts of marked female flies in cages was followed by counting the number of dead individuals each day; the mortality rate of these flies was 0.81% per day-degree (± 3.49 × 10⁻⁴%) and the mean life expectancy was 123.1 day-degrees above a threshold of 11 °C. Mortality rate was shown to increase significantly with average ambient temperature and relative humidity lagged for two sample periods (approximately 10 days). Oviposition rate also increased with average temperature but declined with average relative humidity. A best-fit multiple regression model incorporating both ambient temperature and humidity explained 60.5% of the variance in the pattern of oviposition.
5. The differences between the field and cage populations highlight the caution required when extrapolating life-history parameters from artificial to natural habitats.     

Population ecology of an afro-tropical savanna herb,Lapeirousia rivularis,in Zambia

Detailed demographic studies of herbaceuos plants in afro-tropicalsavannas are extremely rare in published literature. I studied phenology andpopulation dynamics of a perennial herb, Lapeirousiarivularis Wanntorp, at a savanna site in Zambia over a 4-yearperiod, from 1997 to 2001, using enumeration techniques in permanent andtemporary quadrants. The age of the plants was accurately determined frompersistent annual sheaths that accumulate around the corm throughout the lifeofthe plant while the estimated survivorship of the 1998 cohort was developedfroma mathematical model based on the observed mortality of the cohort over a3-yearperiod.L. rivularis completed its annual phenological cycle in asingle rainy season. Plants sprouted from perennating corms in early December,flowered, fruited and dispersed seeds by end of January. Seeds germinatedimmediately after dispersal and seedlings produced small corms before aerialparts died early in the dry season. L. rivularis has twomorphs: a vegetative morph and a reproductive morph; the latter bears severalleaves and flower stalks. In the vegetative morph, the corm is renewed annuallywhile the corms of the reproductive morph did not appear to be renewed. Insteadcorms grew larger and produced lateral daughter corms that became independentramets the following rainy season.Most L. rivularis plants reached reproductive maturitywhen they were 6–10 years old. Reproductive success, seedlingestablishment and recruitment varied from year to year in the grassland plotperhaps because of fluctuations in weather conditions and heavy episodic insectherbivory. The survivorship curve of L. rivularis wascharacteristically concave due to high juvenile mortality (0.2–0.5) andvery low adult mortality (0.03). Although about 3% of the plants live to be upto 30–35 years, the mean age of the population in 2001 was 6.4 yearsbecause of the predominance of juvenile plants. The production of a protectivesheath at the end of the rainy season and the accumulation of old sheathsaroundthe fleshy corm are apparent adaptations against desiccation during the longdryseason drought when the topsoil remains below wilting point. The high juvenilemortality during the dry season is probably caused by inadequate protection bythe few sheaths around the corm against desiccation.Population dynamics in L. rivularis were caused byvariable annual recruitment and high juvenile mortality. Population densitydoubled in 1999 due to good fruiting success in the previous season that wasassociated with good weather conditions and negligible herbivory. Althoughcultivation had a significant negative effect on the population of L.rivularis, it increased consistency in fruiting success andproduction of fruits per plant, presumably because of improvement insoil-moisture status, reduction in plant competition and by providing temporalescape from insect herbivory through delayed flowering. The phenology and lifehistory of L. rivularis exhibit adaptations to a savannaenvironment that is characterized by disturbance and stress caused by seasonaldrought, fire, episodic herbivory and cultivation.     

Comparison of traps for the control of sheep blowfly in the U.K.

The ability of three commercially available trap types to catch Lucilia (Diptera: Calliphoridae) blowflies was assessed on three sheep farms in southwest England in 2008. The aim was to evaluate their relative value for the control of ovine cutaneous myiasis (sheep blowfly strike) on farms. There was a highly significant difference between the total number of female Lucilia caught per day by the traps, with an Agrilure Trap (Agrimin Ltd, Brigg, U.K.) catching more than the other trap types (Rescue Disposable Fly Trap, Sterling International, Spokane, U.S.A.; Redtop Trap, Miller Methods, Johannesburg, South Africa). However, there was no significant difference between the traps in the numbers of female Lucilia sericata (Meigen) caught. Nevertheless, consideration of the rate at which female L. sericata were caught over time showed that the Agrilure trap did not begin catching until about 30 days after its initial deployment. It subsequently caught L. sericata at a faster rate than the other two traps. The data suggest that the freeze‐dried liver bait used in the Agrilure trap required a period of about 30 days to become fully rehydrated and decompose to the degree required to attract and catch L. sericata. Once the bait was attractive, however, the trap outperformed the other two traps in terms of the rate of L. sericata capture. The Agrilure trap would appear to be the most effective of the designs tested for use against sheep blowfly and blowfly strike in the U.K., but care would be needed to ensure that the traps were deployed in advance of the blowfly season so that the bait was suitably aged when trapping was required.     

Evidence for seasonal variation in aggressive behaviour by Macaca mulatta

Observations were made on the Macaca mulatta colony on the island of Cayo Santiago over a period that included two reproductive cycles. The frequency of aggressive behaviour was found to fluctuate cyclically as a function of the colony's reproductive state. Males were wounded and died significantly more frequently during the mating season than at any other time of year. Females were wounded about as often during the mating season as during the birth season, and more died during the birth season than during the mating season, although not significantly so. There was no significant difference between sexes in age at death, nor was there a significant departure from expectation of number of deaths per age class. However, mortality among the reproductively mature males was greater than among mature females. It was suggested that differential injury and mortality rates among adult males might be an indirect result of high levels of androgens which could conceivably alter threshold levels for stimuli initiating severe aggressive interactions.     

Primigravidity,body weight,and costs of rearing first offspring in rhesus macaques

Body size is associated with menarche and ovarian function, but the relationship to first conception is rarely examined. We conducted a longitudinal investigation of rhesus macaques, Macaca mulatta, to determine the effect of differences in body weight on both the age at first conception and survivorship of first progeny. Young females who became pregnant weighed significantly more than peers who remained barren, with weight changes for females who successfully raised offspring no different than those for females who did not produce offspring. Infant mortality among primiparae was not significantly greater than that among multiparae, although nearly twice as high. First-born males tended to have lower survivorship than first-born female offspring. We suggest that reproductive costs encountered by primiparous females are more likely to be modulated by immature neuroendocrine function than by inexperience, small body size, or infant suckling patterns. We conclude that body size influences probability of first conception, socioendocrine factors mediate the likelihood of infant survival, and primiparous production of male progeny seems to exert a greater reproductive cost than does production of female progeny. Am. J. Primatol. 46:135–144, 1998. © 1998 Wiley-Liss, Inc.     

Mean life expectancy of Old World screwworm fly,Chrysomya bezziana,inferred from the reproductive age-structure of native females caught on swormlure-baited sticky traps

Abstract. The reproductive status of native (wild) screwworm fly, Chrysomya bezziana, caught on swormlure-baited sticky traps in Papua New Guinea is described. A total of 1122 females and 25 males were trapped. Of these females 595 were scored for insemination status and stage of ovarian development (on a scale of 2–10) of which 20% were in suitable condition for assignment to first, second and third ovarian cycles. Of the nulliparous females, only 17% were inseminated at stage 3 of ovarian development, 70% at stage 4, 93-97% at stages 5 and 6, and all of stages 7–10 (gravids). All parous females were inseminated. More than half of the captured females were parous (58%) and only 7% of the total were gravid. Proportions of females in ovarian cycles 1, 2 and 3 were 41%, 50% and 9% respectively. Survival of female Ch. bezziana in the laboratory was adequately described by lognormal and Gompertz survival functions, for both of which the mortality rate is an increasing function of reproductive age. Analysis of the reproductive age distribution of native females estimated their mean life-expectancy at 9 days under the prevailing mean field temperature of 26.5^oC. This equates to completion of 1.7 ovarian cycles and an estimated mean lifetime fecundity of 146 female progeny. The survival models, which also allowed responsiveness of females to swormlure-baited traps (female trappability) to vary according to their stage of ovarian development, indicated significant age-dependent trapping bias. These findings are compared with similar data for the New World screwworm fly, Cochliomyia hominivorax.     

Reproductive seasonality in the Indian pygmy field mouse,Mus terricolor

The Indian pygmy field mouse, Mus terricolor, is a tiny, yet economically and ecologically important crop pest found throughout South-East Asia. There are no systematic reports exploring its reproductive physiology. We report the presence of distinct periods of annual reproductive activity and quiescence in M. terricolor. Body weight in males and females, relative weights of testis, epididymis and seminal vesicle in males, ovarian and uterine weight in females, gonadal histomorphic changes, testicular and ovarian cholesterol, sialic acid in epididymis, fructose in seminal vesicle, uterine protein content, melatonin in males and females, testosterone in males, estradiol, and progesterone in females were studied over a period of three years in both wild-caught and lab-acclimated mice. The number of Graafian follicles and corpora lutea, and plasma estradiol and progesterone, along with relative weights of ovary and uterus in females exhibited a peak in the months of October–January, compared to June. Based on histomorphic and hormonal status, the major reproductively active season is the winter (short-day breeding). There is a brief period of sub-maximal reproductive activity in April. M. terricolor is reproductively inactive in the summer, monsoons, and autumn. The results establish M. terricolor as a seasonal breeder in the field, with interesting implications for pest management.     

Growth and reproduction in Canthigaster valentini (Pisces,Tetraodontidae): a comparison of a toxic reef fish with other reef fishes

Synopsis The growth and reproduction of Cantigaster valentini were studied in two sites at Lizard Island, Australia. C. valentini was found to be a gonochore, with a sex ratio very close to 1:1; sexes could be distinguished externally. The growth (in length) of known individuals from both sites was measured at least every two months over two years. Growth rates of males and females decrease as their sizes increase. Growth rates differ between sexes and between sites: males generally grow faster than females and individuals at Mermaid Cove generally grow faster than individuals at Palfrey Island. Spawning is demersal, it occurs daily between 0800 and 1600h, and continues year-round. For females the interval between successive spawnings varies from about 4 days in the warm-water season to about 10 days in the cool-water season. From a comparison of local reproductive output and local recruitment survivorship of larvae in the plankton was estimated to be much higher than in another species (Pomacentrus wardi) for which a similar estimate was available. We suggest that some aspects of the reproductive strategy of C. valentini differ from other, non-toxic reef fishes in ways consistent with a reduced threat of predation upon adults, eggs, and larvae: courtship and spawning are unhurried and occur throughout most of the day; spawning is unrelated to lunar cycles; there is no parental care or defense of fertilized eggs; and embryos often hatch on rising tides.Centre for Environmental and Urban StudiesSenior author's present address: School of Biological Sciences F07, University of Sydney, Sydney 2006, N.S.W., Australia     

Constraints on, and determinants of, the annual number of breeding attempts in the multi-brooded Black Redstart Phoenicurus ochruros

With reference to models predicting patterns of reproduction in multi-brooded species, I analysed some of the factors potentially affecting the number of breeding attempts per season made by female Black Redstarts Phoenicurus ochruros in the central Swiss Alps. The maximum number of successful broods per female per season was three, the median two. The proportion of females initiating only a single clutch per season varied from 16 to 58% over 10 years. Variation in the frequency of single brooding between years was positively related to the date of the onset of breeding. Egg-laying started after a temperature-related threshold value was crossed in April. Females frequently re-nested before fledglings of the previous brood were independent. Short interbrood intervals were associated with triple brooding. The interbrood interval shortened during the breeding season. Intra-individual variation in the number of breeding attempts per season was partitioned according to female age, laying date of the season's first egg (standardized in relation to the median date of first laying within a year) and the occurrence of breeding failures before the ultimate nesting attempt. However, mortality during the season often terminated breeding early, in particular among novice breeder females. Seasonal reproductive success increased linearly with each additional breeding attempt. The productivity of a breeding attempt was independent of the time in the season. Increased reproductive effort affected neither current or future survival nor reproduction of females. The reproductive patterns and trade-offs in multi-brooded Black Redstarts contrast in many aspects with those found in single-brooded species. They are in accordance with models predicting that multi-brooded species are selected to start breeding as early as possible, continue breeding for as long as conditions are suitable, and save time by overlapping broods.     

Collection of field reproductive data from carcasses of the female Eurasian lynx (Lynx lynx)

Information about reproductive physiology in the Eurasian lynx (Lynx lynx) would generate knowledge that could be useful in the management of the Swedish lynx population based on the knowledge about their reproductive potential and population development. Age-related differences in ovulation and implantation rates would affect the reproductive output and the development of the population. The aims of this study were to evaluate a protocol for collection of reproductive data from carcasses by comparisons with published field data and to generate data about reproduction in the Swedish lynx. Reproductive organs from 120 females that were harvested between March 1 and April 9 from 2009 to 2011 were collected and evaluated macroscopically for placental scars. Females had their first estrus as yearlings but did not have their first litter until the next season. Pregnancy rates were lower in 2-year-old females than in females aged 3 to 7 years but did not differ significantly from females aged 8 to 13 years (54.5%, 95.6%, and 75.0%, respectively). CL from the present season were morphologically distinctly different from luteal bodies from previous cycles (LBPC). All females ≥3 years had macroscopically visible LBPC, whereas only 67% of 22 to 23 months old females had one to three LBPC and no females <1 year of age had LBPC. Females aged 34 to 35 months had up to eight LPBC, whereas the highest number of LBPC counted in females ≥3 years of age was 11. These data would be in agreement with only one estrus per season and LBPC from at least three previous reproductive seasons in older females. The number of LBPC was significantly correlated with the weight of the ovaries r_s = 0.648, P < 0.001) and the age of the animals (r_s = 0.572, P < 0.001). Uterine weight differed significantly with the stage of the reproductive cycle and was highest for mature females in the luteal phase of the cycle. The estrous period, defined as occurrence of ovarian follicles lasted from March 5 to April 1 in this material. In conclusion, this study confirms that useful information about lynx reproduction can be collected from reproductive organs retrieved after the death of the animals. Continuous monitoring of lynx reproductive organs would therefore make a valuable contribution to collection of field data, gathering information that can be useful for the management of lynx populations and potentially for the lynx as an indicator of environmental disturbances.     

Sexual selection in sticklebacks in the field: correlates of reproductive, mating, and paternal success

Male sticklebacks display multiple ornaments, and these ornamentshave been shown to be preferred by females in laboratory experiments.However, few field data exist, and it is not known whether thesepreferences are simultaneously or sequentially operative ina single population. We report correlates of reproductive successin two stickleback populations that differ in their ecology,over several periods within their breeding season. In both populationslarger males had higher reproductive success, but not in all periodsof the breeding season. Reproductive success increased withredness of the throat only in the Wohlensee population, andonly in one period that was characterized by low average success.In the Wohlensee population, the parasitic worm Pomphorhynchuslaevis is abundant, and reproductive success decreased withthe presence of the parasite. In the Roche population, maleswith nests concealed in a plant had higher mating success. Thesenests were less likely to fail, suggesting that females preferredto spawn in concealed nests because of higher offspring survivorship.The different sexual traits appear to reveal different aspectsof male quality (multiple message hypothesis): females probablyfind large males attractive because of their higher paternalquality, but it seems more likely that red males are preferred forbetter genetic qualities. Females also discriminate on territoryquality, and male traits may be important in competition forthese territories. The correlates of reproductive success werenot consistent during the season, probably due to changes inthe availability of ripe females. Such fluctuating selectionpressures will contribute to the maintenance of genetic variationin sexual traits.     

Measurement of age and population age structure in the blowfly,Lucilia sericata (Meigen) (Diptera: Calliphoridae)

For field samples of the blowfly Lucilia sericata (Meigen), the degree of wing abrasion, corrected for individual size, was shown to give a useful estimate of age, by calibration against a known measure of chronological age, the fluorescence of pteridines in the head capsule. In more extensive field studies, therefore, wing fray was used to indicate the likely ovarian cycle of each female, after which the length of the most advanced egg follicle was used to give a more precise estimate of age within this cycle. Using these two complementary techniques, the ages of 806 female L. sericata, from two farms in the south-west of England, were estimated over a complete field season in 1996. Analysis of median age of these females revealed distinct peaks and troughs over time. The observed periods of low median age corresponded with predicted periods of high adult emergence; the periods of increasing and high median age corresponded with the predicted senescence of the L. sericata population. Hence, by analysis of population age structure, this study supports the view that fluctuations in abundance of L. sericata, observed in the field, represent the emergence and senescence of relatively discrete generations of adults.     

LIFETIME REPRODUCTIVE SUCCESS,SELECTION, AND THE OPPORTUNITY FOR SELECTION IN THE WHITE-TAILED SKIMMER PLATHEMIS LYDIA (ODONATA: LIBELLULIDAE)

We present estimates of lifetime reproductive success in Plathemis lydia, a territorial dragonfly. We partition the opportunity for selection into multiplicative episodes using the techniques of Arnold and Wade (1984a, 1984b) and measure selection on several morphological and behavioral characters. For both sexes, variance in survivorship was the largest contribution to variance in lifetime reproductive success. Covariance effects are also strong for both sexes, suggesting considerable non-independence of episodes. Opportunity for selection calculated on a daily basis did not approximate analogous values determined from lifetime reproductive success. Phenotypic characters for which we investigated selection included body mass, hind wing length, first date of reproduction, and (for males) an index of territorial aggressiveness. We failed to find any significant direct targets of selection in either males or females. However, the combined effects of direct and indirect selection on early reproduction were significant for males, acting primarily through increased survivorship and increased time per day spent at the pond. Similarly, females present earlier in the season had shorter interclutch intervals. Partitioning of selection acting on male hind wing length and on aggressiveness reveals relationships between selective episodes, possibly indicative of phenotypic trade-offs between natural and sexual selection through male-male competition for females. Division of selection into episodes is a useful technique for identifying the source of selection. However, ordering effects can bias results, except when episodes occur in strictly chronological sequence. We present a method for circumventing this difficulty.     

Sexual differences in reproductive phenology and their consequences for the demography of Baccharis dracunculifolia (Asteraceae), a dioecious tropical shrub

Patterns of phenological variation and reproductive investment were studied in the dioecious shrub Baccharis dracunculifolia DC (Asteraceae), and possible consequences on survivorship were evaluated. The sex ratio was determined in a natural field population (n = 921) of B. dracunculifolia in Belo Horizonte, Brazil. Fifty-two males and 56 females were sampled at random from this population. During the reproductive season of 1999, inflorescence production, shoot growth and mortality, and xylem water potential were recorded for each individual. The population sex ratio was male-biased (1.27 : 1, P < 0.05), and was associated with a higher mortality of female shoots (38.4 vs. 23.1 %, P < 0.05), and individuals (17.8 vs. 11.5 %, P < 0.1), despite lower water stress in female plants. Flowering phenology also differed between the sexes, with males producing more inflorescences, and earlier, than females. Owing to fruit maturation, the number of inflorescences supported by females was higher than that supported by males later in the reproductive season. This occurred during the dry season, and drought stress may have been responsible for the greater female mortality. Thus, the male-biased sex ratio in this population of B. dracunculifolia is probably due to different reproductive functions of males and females. Intersexual differences in reproductive phenology had consequences for plant demography.     

Demographic characteristics of an intertidal bay goby (Lepidogobius lepidus)

Synopsis In a fourteen month study (May 1976 – June 1977) I examined the following characteristics of an intertidal bay goby (Lepidogobius lepidus) in Morro Bay, California, U.S.A.: annual and seasonal patterns of abundance, age composition and growth rates, survivorship and mortality patterns, and the reproductive cycle for female gobies. Fishes were collected with the aid of quinaldine and otoliths and ovaries removed. Age and growth rates were estimated from otolith annuli using a back calculation formula and a Brody-Bertalanffy growth curve. Mortality rates were derived using the methods of Heincke (1913), Robson & Chapman (1960), mean age, and a catch curve (Ricker 1975). A gonad index was used to describe the annual reproductive cycle. Results indicated that abundance fluctuated seasonally and that these fluctuations appeared to be caused by reproductive emigrations. Bay gobies reached an age of 7+ and a standard length of 87 mm. Growth was relatively constant (6 mm yr⁻¹) until age 5, at which point it began to decline. The mean rates of survivorship, mortality, and instantaneous mortality were 0.75, 0.25, and 0.29 respectively. Mortality rates for individual age classes ranged from 0.13 to 0.51 and increased with age. This stock appears to reproduce mainly during the winter.     

Biological Control ofBemisia argentifolii(Homoptera: Aleyrodidae) on Poinsettia with Inundative Releases ofEncarsia formosa(Hymenoptera: Aphelinidae): Are Higher Release Rates Necessarily Better?

The effectiveness of inundative releases of the parasitoidEncarsia formosafor control ofBemisia argentifoliion poinsettia was determined in replicated experimental greenhouses. We evaluated two release rates ofE. formosa:a low release rate (1 wasp/plant/week, released in two greenhouses, in spring 1995) and a high release rate (3 wasps/plant/week, released in two greenhouses, in fall 1993), each over a 14-week growing season. Each release trial had one or two control greenhouses in whichB. argentifoliideveloped on poinsettia in the absence ofE. formosa.Life-tables were constructed forB. argentifoliiin the presence and absence ofE. formosaby using a photographic technique to follow cohorts of whiteflies on poinsettia leaves. Weekly population counts of the whitefly were also made. In the absence ofE. formosa,egg to adult survivorship ofB. argentifoliion poinsettia was 75–81%. At the low release rate, egg to survivorship ofB. argentifoliiwas 5% and parasitism was 13%. At the high release rate, egg to adult survivorship forB. argentifoliiwas 8% and parasitism was 23%. The net reproductive rates (R₀) forB. argentifoliipopulations in the absence ofE. formosaranged from 18.01–26.12, indicating a rapidly increasing population. Net reproductive rates for whitefly populations subject to wasp releases were 1.54 for the low release rate greenhouses and 2.11 for the high release rate greenhouses, indicating substantially reducedB. argentifoliipopulation growth. The low release rate provided better control ofB. argentifoliithan the high release rate. This difference was attributed to higher levels of mortality of whiteflies at the low release rate in the first 5–6 weeks of the growing period. We suggest that mutual interference may also have affected observed levels of mortality and parasitism.     

Age-specific survivorship analysis ofHeliothis spp. Populations on cotton

Population dynamics of Heliothis virescens (F.) and Heliothis zea (Boddie ) (Lepidoptera: Noctuidae) eggs and larvae were studied for two years in a small plot of cotton, Gossypium hirsutum (L.). Due to morphological and ecological similarities, the pooled Heliothis population was considered for most of the analyses. Two generations of Heliothis eggs and larvae were completed during each year. Stage recruitment was estimated for the eggs and larval instars 2–6, and recruitment variances were estimated by a Monte Carlo method. A modified form of the Weibull distribution was developed and used as a model to characterize survivorship curves for each of the four Heliothis generations. A Type I survivorship curve (mortality rate increasing with age) was inferred for both Generation 1 (early season) data sets, whereas a Type II survivorship curve (mortality rate constant and thus independent of age) was inferred for both Generation 2 (late season) data sets. The shapes of the survivorship curves for the individual H. virescens and H. zea populations were inferred to be the same as those for the pooled populations. Analysis of the contributions of various factors to Heliothis stage-specific mortality indicated that natural enemies (predators and parasites) and the availability of food for larvae were responsible for between-generation differences in survivorship patterns.