Winter Generation Research Articles

Life history patterns of some species of Hydropsyche (Trichoptera: Hydropsychidae) in southern Ontario

Life history patterns are described for five species of Hydropsyche in the Credit and Humber rivers. Larvae of univoltine species matured in May or June. Bivoltine species had a fast-growing summer generation of larvae maturing in July or August and a slow-growing winter generation of larvae maturing in April or May. Hydropsyche betteni, H. dicantha, H. slossonae, and H. sparna were bivoltine at some sampling stations, univoltine at others. Hydropsyche scalaris was exclusively univoltine. Most species were represented by many instars concurrently during summer. Overwintering occurred in a smaller number of instars. Species that overwintered in the final or penultimate larval instar were more likely to mature early and to be bivoltine than species overwintering in younger instars. High summer water temperatures and (or) food quality increased growth rates and the probability that a summer generation could mature before fall. Smaller species were more likely to be multivoltine than larger species.Differences among the life cycles of the five species did not suggest effective ecological segregation in summer in terms of larval size. Different overwintering stages among the species may prove to be important factors controlling the number of generations per year.

Reproductive bioenergetics within the summer and winter generations of Euchaeta norvegica (Copepoda)

The predatory copepod Euchaeta norvegica from Korsfjorden, western Norway, has a half-year life cycle. Egg sacs produced by the winter generation are heavier on average than those produced by the summer generation. This is probably determined by the supply of food during the breeding period rather than by the average weight of mature females at the beginning of the breeding period. Measurements on individuals from a Swedish fjord show that the respiratory rate is relatively low and stable over the year. Bioenergetic budgets for the period prior to and during breeding reveal pronounced differences between individuals from the summer and winter generation, the latter being the more efficient at converting energy from a lower trophic level. It is suggested that the most important environmental factor governing this is the abundance of prey organisms.

Bioenergetic and developmental response of a mayfly to thermal variation 1

Egg development, growth, and emergence of Isonychia bicolor were observed in White Clay Creek (Pennsylvania) at ambient temperatures and in fluctuating experimental regimes with diel minima ranging from 12°–12.9°C and maxima between 12° and 20.1°C. Development rate of both eggs and nymphs was correlated positively with increased magnitude of the diel temperature pulse. Adult metamorphosis was most successful in regimes with diel maxima >16°C.Subimago body size and fecundity for winter generation females were about double those for the summer generation. Reducing spring and summer water temperatures lowered the fecundity of winter and summer subimagoes.Weight‐specific respiration rates of nymphs measured at 1.4 constant temperatures (range, 1°–21°C) increased with temperature but were inversely related to body size at a given temperature. Metabolic response to short term (1 h) changes in temperature was immediate; thermal acclimation or compensation was not observed.Energy budgets were calculated for male and female nymphs reared in various thermal regimes. Growth rates, net growth efficiencies, and production:respiration ratios of female nymphs were about twice those of males at all temperatures. Overall net growth efficiencies for I. bicolor averaged 44.16% and P:R ratios 0.84 for the combined sexes.

Observations on the ecology of Simuliidae from the River Frome, Dorset

Abstract. 1. The species of Simulium present at twenty‐seven stations in the River Frome and some of its tributaries are recorded.2. In the lower reaches of the river Simulium omatum and Simulium lineatum have basic life histories comprising four generations of larvae annually.3. At other stations the annual pattern is modified by weed cutting and flow regulations and by position in the river system.4. In winter generations the larvae and pupae are larger than at other times of the year. A survey of the size of pupae at ten stations in October 1973 indicated that temperature could account for variations in size.

Ecological studies of Pirata subpiraticus (BÖESENBERG et STRAND) (Araneae: Lycosidae) II

The life history of Pirata subpiraticus (BÖS. et STR.), was one of the major spiders in East Japan paddy fields, was examined under laboratory conditions.The young spiders that dispersed from the mother's back were reared until maturity, provided the adults of Dorosophira melanogaster and Psilopa spp. as preys, at a constant temperature of about 25°C with 10 hours of daylight.The spiders of the summer generation moulted 5 to 7 times and required an average of 62.7±13.1 days to mature, but the winter nymphs which were collected from paddy fields in October moulted 8 times and required 160.0±8.3 days under the same rearing condition (Table 1). The cause of the significant difference of developmental periods between both generations was not clear. But, this difference may suggest the diapause of winter nymphs of P. subpiraticus that induced by the exposure of the mothers or the eggs to low temperature and short daylength.The carapace widths of the nymphs were measured after each moulting of the winter generation (Table 2). As the carapace widths overlapped between some instars it was impossible to decide the instar by the measurement of the carapace width.The daily food consumption in the immature stages of this species was examined in the summer generation. High predation appeared in the second to forth day after moulting in all instars (Fig. 1). Total food consumptions in each instar increased with advance of the stage, and an average of about 40 flies were killed in the last instar.The daily food consumption of adult females showed 3 peaks occurring after dispersal of the young spiders from the mother's back (Fig. 2 and 3). The peak of food consumption after copulation, however, did not appear when the females mated just after the peak of post-moulting. In cases where other preys than flies were provided, the daily food consumption of these spiders also are described (Table 3-5).

The life history of Diastylis sculpta Sars, 1871 (Crustacea: Cumacea) in Passamaquoddy Bay, New Brunswick

Diastylis sculpta was collected from shallow water (1–15 m) in Passamaquoddy Bay over a 26-month period. D. sculpta produces a rapidly growing and developing summer generation between two successive winter generations. The overwintering generation releases young in mid-July and late August. The summer generation releases young in November. The mean fecundity of the summer-gravid females (78.4) is much greater than the mean fecundity (20.0) of the fall-gravid females. The maximum life-span is 5 months and 12 months for members of the summer and winter generations respectively.

Phenology of the Florida wax scale,Ceroplastes Floridensis Comstock (Homoptera: Coccidae), on citrus in Israel

The phenology of the Florida wax scale (Ceroplastes floridensis) was studied on grapefruit trees in three citrus-growing regions of Israel — the Jordan Valley, the Coastal Plain, and the Yizre’el Valley. This citrus pest develops two annual generations in, all the regions: a ‘summer generation’ which develops from May-June to August-September, and a ‘winter generation’ which develops from August-September to May-June. The mass appearance of the first instar larvae of each generation occurs in May-June and August-September, respectively.

Flight thresholds and seasonal variations in flight activity of the light-brown apple moth, Epiphyas postvittana (Walk.) (Tortricidae), in Victoria, Australia.

The flight activity of Epiphyas postvittana was studied at two sites near Melbourne with the aid of suction traps, over a period of 4 years. Maximum numbers were found to fly during the period September to March with peak activity coinciding with the emergence of winter, spring and summer generation moths. E. postivittana is predominantly a nocturnal flier with maximum activity around 20.00-24.00 h. The lower temperature threshold of flight was 8-11°C. The upper temperature threshold varied from 20-21°C, 24-25°C and 27-28°C for the winter, spring and summer generation moths respectively. Flight was highly influenced by the prevailing wind. The lower wind speed threshold was 0.5-0.8 m-s and the upper wind speed threshold was 2.6-2.7 m-s. The relationship between wind speed and the amount of flight was non-linear, with the frequency of flights decreasing sharply with increasing wind speed. No flights occurred at wind speeds greater than 2.8 m-s. Variation in relative humidity had no influence on flight, but lack of rain favoured flight. The amount of flight activity and the amount of rainfall were negatively correlated; flights did not occur when the daily precipitation exceeded 32.5 mm, and with a precipitation exceeding 39 mm no flights could be expected. The value of these findings to pest control programmes is discussed.

Seasonal Distribution, Reproductive Diapause, and Parasitization of Three Nabis spp. 1 in Southern Arizona 2

Nabis alternatus Parshley, N. americoferus Carayon, and N. capsiformis Germar usually diapaused from October through December in the Tucson and Mesa areas of southern Arizona, though in some years diapause started in September and lasted into February. The winter generation of N. alternatus was unique in experiencing a noticeable color change, but that generation of all 3 species appeared somewhat larger. The ratio of the sexes of all 3 species was ca. 1:1. Nabis alternatus was the predominant species in the Tucson area, N. americoferus was the predominant species in the Mesa area, and N. capsiformis occurred only in the Tucson area. Nabis alternatus and N. americoferus probably have 5 generations per year; all 3 species had 2 main peaks in population each year, one in May and one in November. Two species of tachinids, Hyalomya aldrichii Townsend and Leucostoma simplex (Fallen), commonly parasitized all 3 species. Nabis alternatus and N. americoferus females are rarely parasitized by Wesmaelia pendula Foerster.

Factors Determining Variation in Fecundity of the Light Brown Apple Moth, Epiphyas Postvittana (Walker) (Tortricidae).

The large variation in fecundity in E. postvittana was associated with temperature, larval food plant, time of year each food plant occurs, and low-density larval crowding through mutual interference. Under field conditions, moths from larvae fed on curled dock, apple, plantain, white clover and capeweed laid > 50% of their eggs by 5-7 days old and > 80% by 8-12 days old. Cool conditions produced heavier individuals which lived longer and laid more eggs over an extended laying period. The fecundity and size (pupal weight) were probably influenced by the larval food plant and the time of year of feeding, presumably through seasonal variations in nutritive quality. Low-density larval crowding, despite excess food, significantly reduced fecundity and pupal weight; it occurs under natural conditions of high population density. The combined effect of these factors was cyclic variations in fecundity and size; more fecund, heavier individuals occurred during the cool wet months (winter generation adults) and less fecund, lighter individuals during the warm dry months (summer generation adults); spring generation adults were generally intermediate. The fecundity of E. postvittana can be adequately predicted from the number of egg-laying days.

Bionomics of three species of glossosomatid caddis flies (Trichoptera: Glossosomatidae) in Oregon.

The life cycles of three species of caddis flies of the family Glossosomatidae, Anagapetus bernea Ross, Agapetus bifidus Denning, and Glossosoma penitum Banks, are compared based on monthly collections from Oak Creek and Berry Creek, Benton County, Oregon. Glossosoma penitum, the most abundant species, is bivoltine with overlapping summer and winter generations. Anagapetus bernea and A. bifidus are univoltine with the former being a winter-growing species, and the latter a summer species.Differences in habitat preference occurred, though all three species were collected within a single square meter. Agapetus bifidus is more common in the slower water of glides, whereas G. penitum and A. bernea occur chiefly on the riffles. Anagapetus bernea is more restricted to the headwater regions and small side branches than is G. penitum.A key is provided to distinguish larvae of the three species and the cases are illustrated.

Pharyngeal botfly larvae in white-tailed deer.

Pharyngeal botfly (Cephenemyia spp.) larvae were found in 76 (17%) of 446 white-tailed deer (Odocoileus virginianus) from the Welder Refuge, San Patricio County, coastal south Texas (1961–1968). Seventy-one of the 76 infections by 2nd- and 3rd-stage larvae occurred in deer collected during fall and winter, suggesting a winter generation of approximately 6 months. The highest prevalence occurred in deer from brushy plant communities with a high, relatively continuous canopy. A higher prevalence in mature males (74%) compared with females (29%) during winter was correlated with behavioral differences between sexes during the breeding season.

Life history of the sandy-beach amphipod Neohaustorius schmitzi (Crustacea: Haustoriidae)

Neohaustorius schmitziBousfield, the dominant macroscopic invertebrate on sandy beaches in North Carolina, USA, is strictly intertidal, and distributed from mean low tide to high tide, with an average density of 790/m2. Location of greatest densities within the intertidal zone is dependent upon season and sex. An aggregated distribution is shown. N. schmitzi has 2 generations/year: a winter generation which lives about 8 months, and a summer generation which lives about 4 months. The reproductive season extends from February through October, with spring and summer peaks. Each female appears to produce only 1 brood of young. The number of young ranges from 2 to 14, depending upon the length and generation of the female.

Factors causing seasonal decline inChilocorus bipustulatus L. [Coccinellidae] in citrus groves in Israel

Dissection ofChilocorus females collected in citrus groves at different times of the year reveals a considerable decline in ovogenesis during mid-summer and winter. This decline is not an innate character of the summer or winter generation beetles but is caused by climatic factors, so should not be expressed as aestivation or hibernation. Decreased ovogenesis seems to be the main factor governingChilocorus population decrease during summer. Changes in photoperiod do not hinder egg laying or induce any diapause.chilocorus bipustulatus represents in Israel a potentially multivoltine species whose reproduction during mid-summer or winter is simply slowed down due to unfavorable conditions.

Biology of Trypoxylon in Trap Nests in Wisconsin (Hymenoptera: Sphecidae)

Four species of Trypoxylon were collected in sumac trap nests in Wisconsin: T. frigidum Smith, rubrocinctum Packard, striatum Provancher, and tridentatum Packard, the latter being found in one nest only. Nests of each species consisted of a linear series of cells constructed in borings of 3/16-, 1/4- and 5/16-inch diameter. The average number of cells in nests of T. frigidum and rubrocinctum was about six. Nests of T. striatum averaged five cells, as the cells were longer. The mother wasp provisioned a cell with spiders, laid an egg on the abdomen of one of the last spiders introduced, and sealed the cell with a wall of clay, thus providing a microcosm with shelter and food for each of the prog- eny. A variety of spiders was utilized as prey; most nests contained at least three species, two genera and two families. Theridiid spiders were preferred by T. rubrocinctum, whereas striatum relied miostly on Araneidae. The amount of food in cells was determined primarily on a weight basis. The period of larval growth was about one week. After the larva spun a cocoon, most of the remaining period in the univoltine life cycle of T. rubrocinctum and striatum was passed as a prepupa in diapause. T. frigidum had a summer and winter generation, with the summer generation requiring about one month. Reared adults were asso- ciated with cell location in the nest, and no consistent pattern of sequences of sexes was shown. The nests were parasitized infrequently by Chrysis verticalis Patton, C. pellucidula Aaron, Melittobia chalybii Ash- mead, and miltogrammine sarcophagids in the genera Amobia and Senotaenia.

Seasonal Development of the Southern Pine Beetle in East Texas

The southern pine beetle, Dendroctonus frontalis Zimmerman, passed through 7 (and a partial 8th) consecutive development periods in field-infested bolts kept in an outdoor insectary in east Texas in 1962. This phenomenon suggested that approximately 7 generations may develop each year under favorable forest conditions, A summer generation was complieted in as few as 26 days, but 3½ months were required for a winter generation.

Developmental Changes in Weight and Hemolymph Total Solids in the Sixth Instar of Peridroma saucia (Lepidoptera: Noctuidae)

In spring and winter generations of the variegated cutworm, Peridroma saucia (Hubner), female larvae are heaviest at the fourth day after the fifth ecdysis, their weight decreasing subsequently, but in summer generations their weight continues to increase until the sixth day. Spring and winter males show weight changes similar to those of females of the same generations, but the summer males, in contrast, maintain a constant weight from the fourth to the sixth day after ecdysis. In spring and winter generations, the hemolymph of female larvae has a higher refractive index than that of male larvae at the fourth and subsequent days after the fifth ecdysis, but in summer generations this difference is not evident until the sixth clay. The hemolymph refractive index increases during the prepupal stage. This is at variance with findings on various silkworm species which characteristically incorporate hemolymph proteins and amino acids into silk at this time. It is consistent with previously published work and the analysis of the present findings, to associate the variation in total wet weight and plasma refractive index with the interaction between progressive larval differentiation and metamorphosis phenomena. Upon these are superimposed fluctuations ascribed to sex, genetic change, and host-plant composition. The data obtained in this study suggest that, as a gauge of larval age in populations of healthy insects, plasma refractive index measurements may be more reliable than measurements of wet weight.

Production Rate, Population Density, and Drift of a Stream Invertebrate

Production rates of the stream mayfly, Baetis vagans McDunnough (Ephemeroptera: Baetidae), were estimated by two different methods, compared, and related to population density and drift rate. In the year of study, this mayfly had two summer generations and one winter generation. The two production rate methods yielded estimates of 9.1 and 12.6 g/m2 year as the sum of the three generations, although both estimates were minimal. Production rates for the summer generations were higher than for the winter generation, although winter production was still at a significant level. The summer generations drifted in large quantities, up to about 22 g/day, but the winter generation appeared to drift little, if any, until near the end of the generation in early spring. The relation between annual production rate and mean population density, or turnover ratio, was 9.7, or 3.2 times the number of generations.

Growth and life-cycle of invertebrates from Danish springs

1. The material primarily originates from a thorough study of springs in Himmerland (Jutland) an was collected during thirteen collections in the course of fourteen months. Measurements of the water temperature in the collecting localities were taken at the same time. Measurements of the animals were made with the help of an Edinger Projector. 2. Baetis rhodani has two generations yearly, a long winter generation and a short summer generation. It is possible that these are composed of two generations each. The growth has a stoppage in winter. 3. Brachyptera risi has only one generation per year, which, however, is accomplished in a very short time during winter. There is no marked growth-stoppage in winter. 4. Nemoura (Nemurella) picteti has one generation yearly, stretched over most of the year and with a distinct growth-stoppage in winter. 5. Leuctra hippopus has two generations per year, a longlasting winter generation and a short summer generation. It is not improbable that the material consists of two species, the winter generation being Leuctra hippopus and the summer generation Leuctra fusca. 6. Agapetus fuscipes has one generation yearly. In winter the growth is retarded, or there is perhaps even a stoppage. 7. It has not been possible to draw growth-curves for Crunoecia irrorata, but the histograms show that the species has one generation per year. It must be assumed that there is a growth-stoppage in winter. 8. Pericoma blandula (?) (determination uncertain). The species has one generation per year, with a long period in winter without evident growth. 9. Simulium ornatum has a biennial life-cycle with three generations, having flying times in spring, early summer and autumn. Growth-stoppage takes place in winter. 10. Ancylus fluviatilis takes two years to reach full maturity. Two generations occur simultaneously. The growth stops in late summer and the growth-stoppage is lasting the entire winter. 11. It is not possible from the measurements made to ascertain the growth conditions and life-cycle of Asellus aquaticus. The reason for this is probably that there are several simultaneous generations, and at the same time, the species has a long breeding period. 12. It is not possible to explain the animals' growth-rate by means of temperature conditions in the various localities where the animals were collected. 13. It appears that the nourishment conditions for certain of the species under discussion can offer an explanation of the growth-rate — at the same time, it is difficult to find a correlation for other species. 14. The stony bottom appears to provide a more favourable environment than the other biotopes examined, as the species living on stony bottom seem to complete their growth in a shorter period than species from other biotopes. 15. The same species do not necessarily have the same year-cycle and growth-rate in different localities.

The Outbreak Centres of Schistocerca gregaria, Forsk., on the Red Sea Coast of the Sudan

1. An ecological description of the Red Sea coast of the Anglo-Egyptian Sudan is given, with special reference to the occurrence of the solitary phase of Schistocerca gregaria in its different parts and zones.2. The greatest numbers of solitary Desert locusts were found amongst raingrown dukhn (Pennisetum typhoideum, Rich.) cultivated in the Suaeda belt of the coast, near the sea.3. The factors responsible for the higher population of solitary locusts among the cultivation are probably the soil consisting of soft loose sand, and the more or less evergreen condition of the weeds on cultivated plots. It appears possible, however, that in some localities with naturally loose sandy soil all areas suitable for vegetation are cultivated, and in this case the cultivation in itself is not of primary importance.4. Incipient outbreaks were observed in the type of cultivated areas described above in 1933–34, and again in 1934–35 winter seasons. Hoppers of the phase congregans were found mostly on a weed, Heliotropium undulatum, which is preferred by young hoppers to other food-plants, and seemed to act as a concentrating factor for the hoppers. No hoppers of the ph. congregans were found on clean cultivation where this weed was absent.5. The chief factor determining the commencement of an outbreak seems to be heavy winter rains (over 240 mm. during the season), starting early (end of October) and continuing late (end of February), which allows for the development of two successive winter generations, as follows:—(a) Early maturation of old adults (November); (b) plentiful oviposition of old adults (November-December); (c) hoppers beginning to emerge (end of November); (d) hoppers beginning to become adult (early January); (e) majority of hoppers adult (end January); (f) these young adults remaining among dukhn in a fairly crowded condition (February); (g) young adults maturing (end February); (h) young adults ovipositing (March); (i) hoppers hatching (end of March-April); (j) young hoppers crowded on Heliotropium, assuming congregans coloration and later forming marching bands (April); (k) emigration of young flying swarms (May).6. The exact cause of the rapid maturation of young adults of the first winter generation has not been discovered, although a short period of very high humidity seems to have some effect. There is no doubt that late rains are necessary for most adults to mature and oviposit in the field.7. The Red Sea coast of the Sudan is distinguished from the interior of that country by its higher air humidity, by winter rains, and by the fact that the rainy season can extend for a longer time than the summer rainy period inland. The northern parts of the coast, north of the latitude 20°N., are less likely to produce outbreaks only because heavy and prolonged rains are unlikely to occur there.8. General conditions in Eritrea, south of the Sudanese border, are such that some outbreak areas should be expected to exist there.9. It appears probable that the Arabian coast of the Red Sea also contains some outbreak areas. As regards inland parts of Arabia, their climate, the distribution and the life-cycle of the solitary locusts there, are too little known to estimate the possibility of the existence of outbreak areas, until a special investigation is made.10. The results of the investigations on the Red Sea coast put under suspicion of harbouring outbreak areas of the Desert locust all those parts of the sea-coasts of Africa and Asia which may obtain in some years winter rainfall of not less than 240 mm. extending for a period sufficiently long to allow for the development of two successive winter generations of the locust.