Population dynamics of the phytophagous lady beetle,Epilachna vigintioctopunctata,in an eggplant field in Sumatra

From December, 1981 to December 1982, the population dynamics of the phytophagous lady beetle Epilachna vigintioctopunctata (Fabricius ) (Evp) was studied by mark-recapture of adults and the construction of a life table in an eggplant field in Padang, Sumatra, Indonesia.

1. After planting of the host plants, adults of Evp soon colonized and oviposited massively, resulting in a rapid population growth for 1–2 months; thereafter, the population increase slowed due to defoliation. Three–four months thereafter the host plants recovered their leaves, but leaf quality was less suitable for Evp and, as a result, the population remained at a low level during the rest of the study period. Adult population size fluctuated 7–8 fold during the study period.
2. Adult Evp showed a 1∶1 sex ratio.
3. The daily rate of residence, ψ_i, derived by theJolly-Seber formula fluctuated from 0.9 to 1.0.
4. The estimated mean length of residence of adults was 16.5 days (male) and 15.2 (female), but this was probably much shorter than the actual longevity, because the adults were so active that they flew away or dropped off the plants when they were approached or were slightly disturbed.
5. Adults showed a rich variation in elytral spot patterns. The average number of non-persistent spots per elytron was 0.52 in males and 1.08 in females; 23.3% of males and 24.6% of females had confluence(s).
6. The life table shows that parasitism by wasps, which killed 9.7% of eggs and 35.0% of pupae, and starvation by overcrowding contributed most to the total mortality from egg to adult emergence (>98%).
7. The high dispersal power of adults, coupled with their prolonged l_x−m_x schedules was advantageous for exploiting food plants which were variable in space and time.

     

Population dynamics ofLuehdorfia japonica Leech (Lepidoptera: Papilionidae)

1. An adult population of a papilionid butterfly, Luehdorfia japonicaLeech , was studied by marking, release and recapture procedures in a hilly region in the suburbs of Kanazawa City, Japan.
2. Age of butterflies was estimated from the wing wear conditions, rated as winage categories 0 to 6.
3. Jolly (1965) andSeber's (1973) method was applied to the marking-recapture results for estimating the population parameters (sampling ratio, population size and survival rate).
4. Sampling ratio of males was consistently higher (around 50%) than that of females.
5. Newly emerged females were especially inactive, so that few of them were captured. From day 6.5 to day 10.0 they began to oviposit and became more active and more catchable.
6. An approximate sex ratio of 1∶1 was confirmed from the specimens collected in the field and by rearing experiments.
7. Daily survival rate was about 0.75–0.80 and mean longevity was about 4 days for both sexes. The maximum longevity observed was 17 days, for males and 21 days for females.
8. Dispersal by both sexes of the butterfly was more than 1 km.

     

Estimating the survival rate and mean longevity for adults in a field population of the green rice leafhopper,Nephotettix cincticeps Uhler,by the application ofHokyo andKiritani’s method

Application of the female dissection method proposed byHokyo andKiritani (1967) was attempted in both 1968 and 1969 to estimate the daily survival rate and the mean longevity for the adult population of the green rice leafhopper, Nephotettix cincticeps, in a paddy field. The estimated mean longevity for females was far shorter than the physiological longevity of this species, ranging from 4 to 7 days with some variation between different generations. This could explain the remarkable discontinuity among successive generations which proved to form an important feature of the pattern of seasonal population changes of this insect. Between the two years, the estimated survival rate (and hence the mean longevity also) was negatively correlated to the estimated population size of adults that emerged in either of the two successive generations. This apparent density dependence suggests the possibility that the adult survival, including the effect of dispersal, plays some critical role in bringing about the remarkable population stability from year to year shown by the field population of N. cincticeps.     

A population study in Jamaica on adult Sceliphron assimile (Dahlbom) (Hymenoptera: Sphecidae)

Abstract.

• 1 A mark–recapture study on the sphecid wasp Sceliphron assimile (Dahlbohm), analysed by Jolly's stochastic method (1965), was made from 3 December 1974 to 22 February 1975 at Green Bay, St Catherine, Jamaica.
• 2 Population levels in an 18.2 ha study area fluctuated about a mean of 281 for males, 259 for total females and 87 for reproducing females, while the probable carrying-capacity for these reproductives was about 104.
• 3 Mean estimated daily survival rates were 0.903 for males, 0.924 for total females and 0.945 for reproducing females. For the first two categories these rates decreased (p < 0.02) during the study, probably reflecting increasing emigration. Reproducing females probably do not emigrate and their survival did not significantly decrease.
• 4 Minimum age was linearly related to wing wear (r=+0.69, P < 0.001) and the latter associated with the progressive maturation and ageing of the ovaries. All surviving females become parous by middle age.
• 5 The mean rate of fecundity in the field was dependent on female age and was reduced during prolonged drought. Curves of total achieved fecundity appropriate to realistic survival rates give 4.2–16.8 eggs/female. The Jamaican mean was 9.6 ± 2.3 and that for Green Bay 8.6.
• 6 The proportion of females in the Green Bay population was 0.48 ± 0.03 while 0.55 was expected at emergence.
• 7 A cyclic budget is used to estimate immigration and emigration, and these were important causes of population change.
• 8 For Jamaica, only an estimated 28% of females survived to nest.

     

Population estimate and body size of European pond turtles (<Emphasis Type="Italic">Emys orbicularis</Emphasis>) from Pazarağaç (Afyonkarahisar/Turkey)

Data on population size, adult sex ratio, body size and mass are provided for a population of the turtle Emys orbicularis near Pazara?aç (Afyonkarahisar/Turkey). Using the mark-recapture method (triple catch), a population size of 664 turtles was estimated (95% confidence interval, range 332–996), corresponding to a density of 83 turtles per hectare (range 41.5–124.5). The adult sex-ratio was significantly skewed in favor of males (2.02 males: 1 female; P < 0.001). Almost all recorded specimens were adult (98.1%). Mean straight carapace length (SCL) and body mass (BM) of adult turtles were: SCL = 128.65 mm, BM = 345 g for males (n = 168) and SCL = 135.37 mm, BM = 463 g for females (n = 83).     

Multiple mating and its effect on the reproductive success of female Epiphyas postvittana (Lepidoptera: Tortricidae)

Abstract.

• 1 Multiple mating and its effect on reproductive performance of female Epiphyas postvittana (Walker) moths were studied under controlled conditions.
• 2 The age at which the moths mated for the first time ranged from the first to the tenth day after emergence, but 71% of first matings were during the first 3 days.
• 3 The majority (63%) of females had one or two spermatophores in the bursa copulatrix. Some (24%) were found with three to five spermatophores, whereas no successful mating occurred among 13% of individuals. The number of matings was partly dependent on the number of mates available to the female. Between the range of sex ratios of one male to one female and four males to one female maximal mating success occurred at the ratio of three males to one female.
• 4 Virgin females were capable of egg-laying, but mating stimulated and accelerated oviposition. Mated individuals laid twice as many eggs as unmated ones.
• 5 The level of copulatory activity did not influence the longevity of females irrespective of the number of males available to them.
• 6 Sex ratios with greater than one male to a female improved the reproductive success by marginally increasing fecundity and fertility.
• 7 It is concluded that multiple mating would enhance population growth, and is of particular benefit to populations with a preponderance of females, as is known to occur naturally in this species.

     

Mating system of Bracon hebetor (Hymenoptera: Braconidae)

Abstract.

• 1 We report on the mating system of a field population of the parasitic wasp, Bracon hebetor, on a corn pile infested by the Indian meal moth, Plodia interpunctella. We demonstrate that the mating system is based upon male scramble competition polygyny with male aggregations on high places on the corn.
• 2 The sex ratio among adults was greater than 80% males on the surface of the corn, whereas below the surface the sex ratio was less than 45%. Males actively courted females on the surface, but there were no aggressive interactions among males during courtship or mating.
• 3 Approximately 20% of the females found on the surface of the corn had no sperm in their spermathecae, regardless of age, but the numbers of unmated females decreased later during the day.
• 4 In laboratory studies we showed that females from this population oviposit a female biassed sex ratio, and that only 14% of females were mated before dispersing from their place of emergence.
• 5 Thus sib-mating is unlikely in this gregarious parasitoid. This outcrossing mating system probably arose because of severe inbreeding depression that B.hebetor suffers via a sex locus: diploids that are heterozygous at the sex locus develop into females, but homozygous diploids are male and are generally inviable. The female biassed sex ratio may have evolved in B. hebetor in response to males being the more expensive sex, females dispersing more frequently from the population than males, or a fraction of females remaining unmated in the population.

     

A Polygamous Social System of the Fan-tailed Warbler Cisticola juncidis

The social system of an individually-marked population of the fan-tailed warbler Cisticola juncidis was studied in Japan, over six breeding seasons from 1978 to 1983. More than 127 males established territories, some 50–70% were polygynists each year. Territorial males were replaced frequently within seasons. Females were less faithful than males to their first breeding sites. Perennial or seasonal pair bonds were rare, maintained over two successive breeding attempts, by only 13.6% of females. Half the females left the area after one breeding attempt. Frequent divorce, rapid and multiple remating of females, multiple breedings, and female movement over a wide area all combine to skew breeding sex ratio from unity and favor polygyny.     

Delayed mating and reproduction in the autumn gum moth Mnesampela privata

• 1 The success of mating disruption using synthetic sex pheromones depends not only on preventing mating, but also on delaying mating in the target insect. Using the geometrid pest of Eucalyptus plantations, Mnesampela privata (Guenée), we determined the effect of delaying mating when imposed on males only, females only or on both sexes simultaneously, for 1, 3, 5 and 7 days.
• 2 Delayed mating had a significant negative impact on reproduction, with a 0.89‐fold decrease in the likelihood of mating and a 0.67‐fold decrease in the likelihood of that mating resulting in fertile eggs for every day that mating is delayed. A mating delay of 7 days reduced the mean number of viable eggs laid to 4–13% of that laid by moths paired immediately after emergence.
• 3 Male only imposed mating delays had a significantly lower effect on reducing the likelihood of pairs mating than when both sexes were delayed. A delay imposed on one sex only or on both sexes simultaneously, however, had a similar negative impact on the proportion of fertile matings as well as on the total number of fertile eggs laid.
• 4 Longevity of mated female and male M. privata was significantly different between mating delay treatments, with a significant decline in female longevity when they mated with older males.
• 5 The underlying mechanisms causing a decline in female reproductive output when a mating delay was imposed on males versus females are discussed in relation to the reproductive biology of M. privata and the potential of using mating disruption strategies to control populations in Eucalyptus plantations.

     

Movement and population size of the river sculpinCottus hangiongensis in the Daitobetsu River of southern Hokkaido

Individual movements and population size of the amphidromous sculpinCottus hangiongensis, excluding young-of-the-year smaller than 50 mm in body length, were studied from October 1983 to December 1984 in 5 separate sections of the Daitobetsu River of southern Hokkaido, by using mark-recapture methods. During the non-breeding season, distinct inclinations in density, body length distribution and sex ratio ofC. hangiongensis populations were found along the course of the river. The population density was the highest, 3.45 per m², in the lowest section and decreased in the upper sections. Larger males were found in larger numbers toward the lower reaches, whereas the sex ratio, which was biased in favor of females, was generally more striking upstream. These characteristics of the population structure may result from the amphidromous life history and the polygynous mating system of this species. Many marked fish were recaptured within the original sections, where they had been marked and released, throughout the year. During the non-breeding season, especially, the mean movement was 40.6 m, with the greatest movement being 92 m. During the breeding season, on the other hand, some sculpins appeared to move downstream before spawning and upstream after spawning. Such downstream spawning migration may increase the chance of encountering a mate, and for females it may enhance the chance of encountering larger males. Moreover, it may also contribute to a decrease in the mortality rate of their flowing larvae.     

Population dynamics of the solitary digger bee<Emphasis Type="Italic"> Andrena vaga</Emphasis> Panzer (Hymenoptera,Andrenidae) studied using mark-recapture and nest counts

The population size of the solitary digger bee Andrena vaga was documented using mark-recapture methods during 4 consecutive years (1996–1999). Additionally, the numbers of the parasitoids Nomada lathburiana and Bombylius major were estimated. For calculations of the daily population size, the Jolly-Seber model for open populations with time-dependent survival and capture rates was used. The mean daily population size corresponded well to the number of nests marked in the aggregation of A. vaga. The method of mark-recapture achieved the most accurate data when the number of sampling periods and the capture probability was high. The results document a decrease in population size of the investigated A. vaga aggregation during 4 successive years. A population increase of its parasitoids B. major is considered to be one reason for the population decline of A. vaga in 1999. The sex ratio of A. vaga was biased toward females, contrary to the expected higher number of males. Results of the mark-recapture studies showed that up to 50% of females left the aggregation or died at the beginning of the season. The females probably colonized new aggregations at distances further than 200 m away from their birth aggregation, as no marked females were observed in the environs of the study area. This behavior is interpreted as a parasite avoidance strategy. The bee populations in the study area form a web of interconnected aggregations. Apparently a flux of extinction and recolonization exists between the different aggregations.     

Seasonal biological variation in some leaf-miner parasites in the genus Achrysocharoides (Hymenoptera, Eulophidae)

ABSTRACT.

• 1 Most Achrysocharoides species and their Phyllonorycter hosts (Lepidoptera, Gracillariidae) have two generations per year in Britain.
• 2 In those species with separate sex broods, peak male emergence tends to be earlier than peak female emergence. This female emergence lag is shorter in the second generation.
• 3 The mean brood size in the second generation is significantly smaller than in the first in A.cilla males and females, A.latreilli females, mixed sex broods of A.atys, and A.carpini females. A.cilla, A.latreilli and A.niveipes generally have a significantly greater proportion of males in the second generation, but A.atys does not.
• 4 There is a shift to killing later instar Phyllonorycter larvae in the second generation, when a much higher percentage parasitism is generally achieved.
• 5 The intergeneration differences in sex ratio and brood size may be explained by a change in oviposition behaviour of females of the first and second generations.

     

Use of cloacal sexing techniques in mark-recapture estimates of breeding population size in Wilson's stormpetrel Oceanites oceanicus at South Georgia

Summary Many stormpetrel species breed in habitats where their populations cannot be estimated by direct counts of burrows or birds; mark-recapture experiments have been confounded by the presence of many wandering non-breeders. With a population of Wilson's Stormpetrel Oceanites oceanicus at Bird Island, South Georgia, we tried to estimate the proportion of breeding females in samples obtained during a mark-recapture experiment. These were identified by measurements of the cloaca, which greatly enlarges at egg-laying. A concurrent experiment with individually marked birds determined that breeding females could be discriminated from males and non-breeders for c 30 days after laying. The technique is probably applicable to other petrels, though it will work best with those that lay most synchronously. The overall population estimate was 4841–5515 birds (SE 856–1417); estimates of breeding females gave a population of 2300 paris early in the incubation period and 1400 pairs near hatching.     

The impact of sarcoptic mange Sarcoptes scabiei on the British fox Vulpes vulpes population

• 1 Disease epizootics can significantly influence host population dynamics and the structure and functioning of ecological communities. Sarcoptic mange Sarcoptes scabiei has dramatically reduced red fox populations Vulpes vulpes in several countries, including Britain, although impacts on demographic processes are poorly understood. We review the literature on the impact of mange on red fox populations, assess its current distribution in Britain through a questionnaire survey and present new data on resultant demographic changes in foxes in Bristol, UK.
• 2 A mange epizootic in Sweden spread across the entire country in < 10 years resulting in a decline in fox density of up to 95%; density remained lowered for 15–20 years. In Spain, mange has been enzootic for > 75 years and is widely distributed; mange presence was negatively correlated with habitat quality.
• 3 Localized outbreaks have occurred sporadically in Britain during the last 100 years. The most recent large‐scale outbreak arose in the 1990s, although mange has been present in south London and surrounding environs since the 1940s. The questionnaire survey indicated that mange was broadly distributed across Britain, but areas of perceived high prevalence (> 50% affected) were mainly in central and southern England. Habitat type did not significantly affect the presence/absence of mange or perceived prevalence rates. Subjective assessments suggested that populations take 15–20 years to recover.
• 4 Mange appeared in Bristol's foxes in 1994. During the epizootic phase (1994–95), mange spread through the city at a rate of 0.6–0.9 km/month, with a rise in infection in domestic dogs Canis familiaris c. 1–2 months later. Juvenile and adult fox mortality increased and the proportion of females that reproduced declined but litter size was unaffected. Population density declined by > 95%.
• 5 In the enzootic phase (1996–present), mange was the most significant mortality factor. Juvenile mortality was significantly higher than in the pre‐mange period, and the number of juveniles classified as dispersers declined. Mange infection reduced the reproductive potential of males and females: females with advanced mange did not breed; severely infected males failed to undergo spermatogenesis. In 2004, Bristol fox population density was only 15% of that in 1994.

     

Longevity costs of same‐sex interactions: first evidence from a parasitic wasp

Costs of sexual interactions play a key role in life‐history evolution. Although the costs of reproduction have been investigated in both sexes of many insects, the costs of same‐sex interactions have been examined in few species. In parasitic wasps, very little has been reported about the longevity costs of heterosexual interactions, and nothing is known about longevity costs of same‐sex interactions. In this study, the effects of heterosexual and homosexual activities on longevity were evaluated in Psyttalia concolor (Hymenoptera: Braconidae), a synovigenic koinobiont larval‐pupal endoparasitoid of tephritid flies. When compared with individually housed virgin wasps, male longevity was strongly reduced both in males kept with females, and in males kept with other males. When females were kept with males, their longevity was reduced compared with the virgin females and females kept with other females. Overall, the costs of male–female interactions were considerable in both sexes of P. concolor, while same‐sex activities were found to be costly only among males, suggesting that they may have implications for the evolution of the P. concolor mating system.     

Host population structure affects field sex ratios of the heteronomous hyperparasitoid, Coccophagus atratus

Abstract.

• 1 Second instar Filippia gemina de Lotto scale insects are the preferred hosts of female Coccophugus atrutus Compere larvae. These scale insects were found on their host plants, Chrysanthemoides monilifera Norlindh and Cliffortia strobilifera Mettenius, only at certain times during a 1 year sampling programme.
• 2 Late larval instars and prepupae of C.atratus, and a Metaphycus species, are the preferred hosts of male C.atratus larvae. These hosts, although they occurred on the same host plants as hosts for female C.atratus, were most numerous at different times during the sampling period.
• 3 The ratio of hosts suitable for C.atratus varied from a predominance of hosts suitable for females through to a predominance of hosts suitable for males. Sex ratios of adult C.atratus followed a similar trend but did not reflect, exactly, the ratio of available hosts. Differences in mortality between sexes and hyperparasitism may account for this anomaly.
• 4 Variable population sex ratios observed in C.atratus apparently result from the behaviour of individual females in which brood sex ratios are dependent on the relative availability of hosts for males and hosts for females. This behaviour, in turn, may result from variability in the host population structure but may also result from selection pressures operating at the time that heteronomous hyperparasitism evolved.

     

Life expectancy,maximum longevity and lifetime reproductive success in female Thornicroft's giraffe in Zambia

Gestation and longevity scale with body mass across taxa, yet within size dimorphic taxa, males tend to have reduced lifespans compared with females. Testing life history models, and accounting for sex differences in longevity, requires obtaining accurate longitudinal data from wild populations. We provide the first report describing key life history parameters from a long‐term study of giraffes in Africa. We followed a population of Thornicroft's giraffe (Giraffa camelopardalis thornicrofti) in Zambia for over 40 years. Maximum longevity among females was approximately 28 years, with lifespan accounting for 81% of the variance in lifetime reproductive success. Average adult female life expectancy was no different than average adult male life expectancy. However, the breeding lifespan of males was about half that of females, while maximum lifespan of males was 75% that of females. Our findings support the suggestion that sex differences in maximum lifespan arise from stronger selection for lengthy lives in females than in males. Among females, longer lives are associated with greater reproductive output.     

Structure and projected decline of a Karoo dwarf tortoise population

Inconspicuous, secretive, or sparsely distributed species receive relatively little research attention, potentially leading to uncertainty about their status and lack of efforts to conserve them. Karoo dwarf tortoises (Chersobius boulengeri) are endemic to South Africa, spend most of the time in retreats at remote arid locations, and are seldom seen. We conducted a 3-year (2018–2020) mark-recapture study to investigate the size and structure of the only Karoo dwarf tortoise population currently known to exist. The population in the 16-ha core of our study site consisted primarily of adult males and females, at a density of 3.3 individuals/ha. Many individuals had severely worn shells and appeared old. Small individuals (straight carapace length <65 mm) represented just 8% of the population and were mostly recent hatchlings. Overall, tortoises had high estimated survival rates (0.77–0.95; lower 95% confidence limit for the smallest tortoises was 0.16), despite a 15-month drought. The lack of small individuals may reflect low levels of recruitment and population decline. Predation by corvids was an obvious threat to all size classes. We estimated that the local population across the 250-ha study area was 800–900 males and females, and recommend precautionary conservation measures focused on reducing human-subsidized avian predation.     

Life table studies on the paddy field population of the green rice leafhopper,Nephotettix cincticeps Uhler (Hemiptera: Cicadellidae), with special reference to the mechanism of population regulation

The population growth of the green rice leafhopper, Nephotettix cincticeps, in the paddy field was analyzed based on the life table data accumulated for six years. The paddy field population, which stems from the invading adults of the first generation (G-I), repeats two complete generations, and the hatchlings of the fourth generation (G-IV) enter diapause and overwinter as the fourth instar nymphs in fallow paddy fields. It was clarified that the density dependent reduction in the mean longevity and oviposition rate of adult females in G-II and III played a primary role in stabilizing the annual population densities. The annual average of the mean longevity of G-II females (3.9 days) was much shorter than that of G-III ones (7.7 days) and thus the density dependent reduction in the mean longevity induced a more prompt regulatory effect on the oviposition of G-II females compared with G-III ones. As the result, two equilibrium densities of eggs were obtained, e.g., ca 100 and 700 eggs per hill in G-III and IV, respectively. Density dependent decrease in the proportion of mature females in the adult population was especially conspicuous in G-II, and this was closely associated with the density dependent reduction in the mean longevity and fecundity. Thus, the density dependent dispersal (emigration) of the adult females by flight in G-II and III was the most convincing factor in the process of population regulation. The density dependent dispersal of the adult females is effective in avoiding the deleterious effects of nymphal crowding in a breeding habitat unit (a paddy field), and may result in a more even distribution of the population over a continuous habitat units in a locality than otherwise.     

Biological traits of Epitrix papa (Coleoptera: Chrysomelidae: Alticinae), a new potato pest in Europe,and implications for pest management

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