Maximum Reproductive Potential Research Articles

Once-Mated Beet Armyworm (Lepidoptera: Noctuidae): Effects of Age at Mating on Fecundity, Fertility, and Longevity

We studied the effects of age at mating on reproductive parameters for once-mated beet armyworm, Spodoptera exigua (Hubner), moths in the laboratory. The age of moths at mating significantly influenced the transfer of spermatophores by virgin males and the receipt of spermatophores by virgin females. Female age at mating significantly affected fecundity, fertility, and longevity. Two days after emergence was the optimum mating age for females to achieve their maximum reproductive potential. However, females laying the greatest number of eggs lived the fewest number of days. Male age at mating significantly influenced the fecundity and fertility of their mate and their own longevity. Females mating with 2-d-old males laid the most eggs and had the highest fertility. Males mating on day 2 after emergence lived significantly fewer days than males that mated on day 1 or on days 10 or 11. To document the effects of an adult mortality factor on S. exigua reproductive potential, the age at which moths mate must be standardized.

Size At Sexual Maturity in Red Shrimp Females, Aristaeomorpha Foliacea, From the Sicilian Channel (Mediterranean Sea)

Abstract This paper reports on the maturity pattern and the estimation of length at sexual maturity for Aristaeomorpha foliacea females, based on two years of seasonal research trawl surveys. Two approaches were used: gonadic condition (empirical scale) and presence/absence of spermatophores. Ready-to-spawn females (IV stage) occurred almost exclusively in summer throughout the area surveyed. Distribution of the proportion of "mature" (III + IV stages) females showed the classic "sigmoid" shape but with a general failure to attain 100% maturity, even though in the largest size classes there is substantial inter-year variability. The presence of spermatophorcs, however, being a sign of adulthood, with almost all the medium/large specimens positive, showed a better approximation to the sigmoid curve. An attempt to combine the two curves, in order to more precisely identify the length at maturity, is illustrated and discussed. The logistic model has been chosen in a form that allows the asymptote to be < 1. The maximum reproductive potential is defined as the point of intersection of the two curves (spermatophores and maturity). This maximum is reached after about 18 months, at a carapace length of 40 mm.

Reproductive capacity of the horse chestnut scale insect, Pulvinaria regalis Canard (Hom., Coccidae)

AbstractThe surface area of pre‐oviposition female scale insects was closely correlated with their dry and wet weight biomass, and was used as a convenient, indirect method of adult size assessment. Adult females at oviposition were on average bigger when in low density populations than those in high densities, an indication of intraspecific competition in the nymphal stage. Larger females were found to be more fecund (laid more eggs), and produced larger eggs, than smaller females. No significant differences were detected between fecundities of females which had fed as nymphs on different species of host tree, and the general adult size/fecundity relationship was of sigmoid form, indicative of a maximum reproductive potential, which was independent of host tree species. Comparisons with other Hemipteran species indicated the generalist nature of P. regalis, adapted to widespread dispersal and large first instar losses from populations.

The reproductive cycle of the scallop Argopecten circularis (Sowerby, 1835) in relation to temperature and photoperiod, in Bahia Concepcion, B.C.S., Mexico

The reproductive cycle of the scallop Argopecten circularis, an important resource of the fisheries in Baja California Sur, was studied in relation to exogenous factors such as temperature and photoperiod in Bahía Concepción. Monthly samples of adult specimens were used, and biometric data for the shell and soft body parts were recorded. The gonads were analysed histologically and five phases of gonadal maturation were described. This species was confirmed to be functionally hermaphroditic, with a reproductive pattern characterized by a period of maximum activity from December to March, when the dominant phases are maturity and spawning. The prevailing conditions during the main spawning peak were: water temperature between 16 and 22ºC, and photoperiod between 630 and 760 minutes of daily average illumination per month. The first maturation of the gonads, determined histologically, occurred when the organisms had an anteroposterior length of 35 mm. Spawning can occur at 47 mm. The minimum size for maturity and spawning in the general population was 58 mm. We determined that maximum reproductive potential starts at this size, and coincides with the lowest water temperature in the annual cycle. The annual variations in the spawning periods of this species, in different parts of Baja California Sur, suggest flexibility in the influence of exogenous factors and endogenous controls on the reproductive event.

Laboratory evaluation of Brazilian Mesocyclops (Copepoda: Cyclopidae) for mosquito control.

In laboratory tests, four different strains of Mesocyclops aspericornis (Daday) collected in or near Fortaleza, Brazil, showed potential as biological control agents of Aedes aegypti (L.) mosquito larvae but were not as effective against Anopheles or Culex. In contrast, the larger M. longisetus (Thiebaud), collected at Fortaleza, killed 100% of Ae. aegypti and Anopheles farauti (Laveran) (No. 1) at larval densities of 200/liter and Culex quinquefasciatus (Say) at 25/liter. In cage simulations with Ae. aegypti and Mesocyclops, both copepod species eliminated all immatures in earthenware pots by week 3. Owing to the lack of replacement, all Ae. aegypti adults subsequently died by week 8 or 9. Although both M. longisetus and M. aspericornis showed maximum reproductive potential at 25 degrees C, breeding occurred from 20 to 35 degrees C. Based on these laboratory evaluations, M. longisetus has been selected for field trials in rural villages in Ceará to control Ae. aegypti.

Effect of host age, parasitoid age and temperature on interspecific competition between Chelonus insularis Cresson, Cotesia marginiventris Cresson and Microplitis manilae Ashmead

The effects of host age, age of Cotesia marginiventris Cresson adults and temperature on interspecific competition between fall army worm (FAW), Spodoptera frugiperda (J. E. Smith), larval parasitoids C. marginiventris, Microplitis manilae Ashm. and the egg-larval parasitoid, Chelonus insularis Cresson were studied. All parasitization results for C. marginiventris and M. manilae were from FAW larvae parasitized as eggs by C. insularis. The maximum reproductive potential for C. marginiventris was achieved in hosts initially parasitized by C. insularis and were 36 to 48 hours old and at a temperature of 25°C. No host discrimination was found for C. marginiventris between larvae containing a developing C. insularis and non-parasitized larvae. The optimum parasitoid age for C. marginiventris during the host exposure period was 48 to 96 hr. Younger or older parasitoids were not able to compete as successfully against C. insularis. A sex ratio of approximately 65% males was present in C. marginiventris progeny produced from parents ranging in age from 24 to 108 hr old. Egg to adult development times at 25°C were 17 and 26 days for C. marginiventris and C. insularis, respectively. In multiple parasitized larvae, C. marginiventris appeared to physically attack and destroy the larvae of C. insularis. However, M. manilae larvae died after 6 days without appearing to have been physically attacked in hosts containing C. insularis.

Pollination intensity and potential seed set in Passiflora vitifolia.

Initial seed set and fruit set were pollen-limited in a Costa Rican population of Passiflora vitifolia, a self-incompatible species with 200-350 ovules per flower. Pollination intensity was measured by counting the number of allogamous pollen grains on stigmas of the large one-day flowers. Hand-pollinations demonstrated that 25-50 pollen grains are required for fruit set, and >450 are needed for maximum seed set, with a pollen:seed ratio of about 1.6:1.0. Hummingbirds (Phaethornis superciliosus) delivered sufficient allogamous pollen for maximum seed set to only 28% of the flowers examined. Naturally pollinated flowers yielded fewer fruits and fewer seeds per fruit than those pollinated by hand. Most pollen transferred by humming-birds was self-incompatible; emasculated flowers yielded higher seed set than flowers with intact anthers. Visitation rates did not provide a good index of effective pollination.There were significant differences in ovule number, maximum seed set, and maximum per cent seed set among individual vines. More than half of an individual's flowers failed to set fruit, whether pollinated by birds or by hand. In this population, maximum reproductive potential may be limited by maternal resources for fruit development, but seed set varies with pollination intensity. Pollen-limited seed set may be a disadvantage of self-incompatibility, especially in species with many-seeded fruits.

Experimental studies of a benthic predator-prey relationship. I. Feeding, growth, and egg-collar production in long-term cultures of the gastropod drill Polinices alderi (Forbes) feeding on the bivalve Tellina tenuis (da Costa)

Groups of naticid gastropod drills, Polinices alderi (Forbes) were kept in constant temperature laboratory culture, using the bivalve Tellina tenuis (da Costa) as prey, for periods in excess of 2 yr, to study rates of feeding, growth, and egg collar production. Following an initial growth phase, further growth, egg production, and food consumption all showed a clear annual cycle of variation in those cultures which contained both sexes. During the growth phase, growth rates varied with temperature with the highest rates at 20°C; in this phase, temperature and predator size accounted for most of the variation found in rates of predation and food consumption. During the reproductive phase, somatic growth was small and showed no temperature dependence; in this phase, temperature and rate of egg collar production accounted for most of the variation found in rates of predation and food consumption. In single sex cultures there was no egg production but, in separate experiments, isolated mated females continued to produce eggs >1 yr after isolation. Maximum rates of egg production were found at 15–20°C. The maximum reproductive potential, at 15°C, was equivalent to 10 times the mean tissue mass during a single annual reproductive period. Neither the timing nor duration of the reproductive period was significantly different at 10, 15 or 20°C, but there was no egg production at 25°C.

The Effect of Arprinocid on the Reproductive Potential of a Field Isolate of Eimeria tenella

Oocyst production by an isolate of Eimeria tenella propagated from birds medicated with 50 ppm arprinocid was compared with that of the same isolate propagated from unmedicated birds. Statistically significant (P less than 0.05) reductions in oocyst production were found for the drug-exposed isolate for inocula levels of 64 and 250 sporulated oocysts per bird. Numerical reductions were observed for inocula levels of 1,000 oocysts per bird, but with higher levels of inocula, no differences were seen. Inhibitory drug effects for the inocula levels of 64 and 250 oocysts per bird appear to be meaningful because they coincide with the maximum reproductive potential (oocysts produced per oocyst inoculated). The results indicated that significant information can be masked by excessive inoculum with consequent crowding and reduction in reproductive potential.

Reproduction of the American Dog Tick, Dermacentor variabilis1 , under Laboratory and Field Conditions

Female American dog ticks, Dermacentor variabilis (Say), engorged on an albino rat, wild-caught porcupines and a raccoon, were held at 6 constant temperatures in the laboratory and at fluctuating temperatures at ground level in grassland and woodland of a study area in southwestern Nova Scotia. Mean weights of engorged females ranged from 309.4 to 665.9 mg following detachment from porcupines and the raccoon, respectively. The highest mean total number of eggs deposited per female engorged on porcupines and the albino rat and held at 25°C was 4877 (range 597–7187). The number of eggs laid and weight of engorged preoviposition ticks were positively correlated for most temperatures except that at the suboptimal constant temperatures of 15° and 35.6°C the correlations were still positive but not statistically significant. The pattern of daily oviposition rates varied in shape and magnitude of peaks depending on the temperature at which the ticks were held. The avg peak daily oviposition was as high as 528 eggs/female on the 3rd day of oviposition and as low as 79 eggs/female on the 32nd day of oviposition for the ticks held at 29.7° and 15°C, respectively. Fluctuating temperatures in grassland and woodland and the porcupines and raccoon as hosts during May and June, 1976, were suboptimal for female ticks which produced less than half the mean total number of eggs that were produced by females engorged on the albino rat and held at a constant 25°C during the same period. Ticks feeding on the 3 host species produced viable eggs which had similar weights during the peak oviposition period. The viability of eggs was reduced towards the end of the oviposition period. Under field conditions, less optimal temperature ranges may reduce the maximum reproductive potential of D. variabilis .

Effect of Temperature Environment and Laying Cages on the Reproductive Performance of Turkeys

This study was designed to determine the effects of (1) environmental temperatures of 20°, 23° and 26° C., (2) laying cages vs. conventional litter floors, and (3) limestone flour vs. granulated limestone on the reproductive performance of Large White turkey hens for a 24-week experimental period.Females in an environmental temperature of 26° C. laid significantly (P ≤ 0.05) fewer eggs on the average than those maintained at temperatures of 20° and 23° C. (51.6 vs. 64.0 and 60.0 eggs, respectively). Egg shell breaking strength showed no consistent trend with increased temperature. Percentage settable eggs, fertility, hatchability and feed consumption were unaffected within the range of environmental temperatures imposed.Females in laying cages showed an increase in egg production, a lower percentage of settable eggs, poorer egg shell thickness and egg shell breaking strength, an increase in feed consumption, and reduced fertility and hatchability compared to those in conventional litter pens. Indications from the plasma calcium concentrations were that the egg shell quality problem in caged hens may be related to calcium metabolism.Neither the ground limestone nor the #10-limestone particle diets had any effect on the parameters measured.Data showed that maximum reproductive potential for Large White turkeys was expressed at temperatures between 20° and 23° C. in conventional litter floor pens under the conditions of this study.

Life cycle studies with Eimeria magna Pérard, 1925.

Excystation of Eimeria magna required exposure to CO2 at body temperature followed by trypsin and bile. Incubation in the presence of CO2 produced marked effects on the inner layer of the oocyst wall. The evidence suggests that CO2 stimulates enzymic activity from within the oocyst rather than exerting a physico-chemical effect on the oocyst wall from the outside. Released sporozoites measured 19.65 X 3.33 mum. In the rabbit, E. magna undergoes at least 5 cycles of asexual schizogony before gametogony takes place. First-generation schizonts were observed at 30 hr, measured 15 X 11 mum and contained 4, 6, 8 or occasionally 12 merozoites; the merozoites were characterised by two very large and prominent refractile granules. As the infection progressed, schizont size and merozoite numbers became more variable; some schizonts contained 2-8 fat merozoites, many probably multinuclear, while other schizonts contained 12-100 thinner merozoites. First generation schizogony took place in the glands; all subsequent stages developed in the upper parts of the villi of the small intestine. Sexual forms have been seen as early as 96 hr, but maximum sexual activity was noted at 120-192 hr. Oocysts measured 35.87 X 24.05 mum. The first oocysts were passed 6-7 days after inoculation, with peak production at 8-9 days. Sporulation was optimal at 30 degrees C; higher temperatures inhibited sporulation, and were in time lethal, while sporulation would take place normally after suppression by cold for at least 11 months. Single oocyst inoculations indicated a maximum reproductive potential of 26.15 million. Pathogenic effects were mostly mild, amounting to growth depression over days 4-7 and softening of the faeces; occasionally diarrhoea and/or death occurred.

Reproductive Cycle and Growth in the Lizard Anolis acutus

Anolis acutus is an endemic species and only anole on the island of St. Croix, U. S. Virgin Islands. A high percentage of ovigerous females are present during most of the year, with January thru April being the months of lowest reproductive potential. However, even during these months ovigerous females may exceed 50% of the adult females. Reproduction can take place during all twelve months of the year. Maximum testes size occurs from June thru October. In females fat bodies were rarely large, and were smallest during the dry season (December-April). Fat body size showed no temporal pattern in the males. Maximum reproductive potential is correlated with months of high rainfall, and the lowest reproductive potential with months of low rainfall. Females lay a single egg at a time. Eggs range from 10.7-11.4 mm long and 7.4-8.6 mm wide and are buried in sandy or gravelly soils. Fourteen days after laying eggs weigh 0.32 g. Hatching occurs in about 30 days at 28 C. Hatchlings are 19-21 mm snout-vent and weight 0.21-0.30 g. The average growth rate of juveniles is 0.07 mm/day, of females it is 0.06 mm/day, and of males, 0.11-0.14 mm/day. Females apparently reach sexual maturity in less than a year and males in about one year. Minimum size of sexually mature females is 36 mm snout-vent, and their maximum size is 49 mm. Males appear to reach sexual maturity at about 50 mm snout-vent and reach a maximum size of 67 mm.