Temporal Pattern of Pinewood Nematode Exit from the Insect Vector Monochamus carolinensis

Laboratory-reared Monochamus carolinensis (Olivier) were used to study the temporal pattern of pinewood nematode dauer larval exit from this beetle vector. Exit rates of dauer larvae were determined by comparing the mean number of dauer larvae carried by adult beetles 0, 7, 14, or 21 days after emergence from the log in which they developed. Density of dauer larvae was highest in beetles on the day of their emergence and dropped slowly through the subsequent age classes. The rate of nematode exit was low during the first week (4.5%) and higher during weeks 2 (20.5%) and 3 (13.1%). A total of 38.1% of the initial dauer larvae exited the beetles during the 3-week observation period.     

Tillage compromises weed seed predator activity across developmental stages

Granivorous ground beetles (Coleoptera: Carabidae) are ubiquitous throughout temperate agricultural systems, and reduce weed seedbanks. However, trade-offs may exist between tillage frequency and ecosystem services of invertebrate seed predators, especially those in the larval stages, which have relatively poor resistance to disturbance. While much research has focused on adult activity patterns and the conservation biocontrol services they provide, almost nothing is known about carabid biology and habitat requirements during larval stages, despite the fact that adult recruitment is determined by factors that promote larval survival. We present data on larval and adult Harpalus pennsylvanicus Dej., a common weed seed predator across North America, from two experiments examining its activity density across tillage and cover-cropping treatments in organic tomato systems. Larvae emerged 4–6 weeks after the adult activity peak, and larval activity density was up to 10 times higher in no-till crop environments than in cultivated areas. After a long disturbance interval, seasonal cultivation had no effect on foraging activity of adults, but reduced larval activity density in both experiments. Additionally, larvae positively correlated with living weed biomass in no-till treatments, suggesting the importance of plant-based resources in oviposition site choice. Compared with adults, larvae are relatively immobile and vulnerable to disturbance; thus, weed management strategies that rely on frequent cultivation may undermine the ecosystem services provided by granivorous insects.     

Absence of metabolic cold adaptation and compensatory acclimation in the Antarctic fly, Belgica antarctica

The respiratory metabolism in larvae of the Antarctic fly, Belgica antarctica Jacobs (Diptera: Chironomidae) was investigated at Palmer Station, Anvers Island (64°46′S, 64°03′W). Oxygen consumption was linearly related to temperature from 0 to 20°C, respectively, 49 and 338 nl/mg live wt/hr. Maintenance at 0 and 10°C for 8 days had no differential effect on the metabolic rate, suggesting that larvae lack the ability for compensatory acclimation. A comparison of standard metabolism for polar and temperate chironomids revealed no elevation of metabolic rate in polar forms. However, polar species exhibited lower activation energies than temperate forms indicating that the respiratory metabolism of polar chironomids is relatively temperature independent.     

Effects of sub-lethal cold stress on the Western Flower Thrips, Frankliniella occidentalis

In order to establish in a new geographical area, introduced insects must be able to survive any period of adverse conditions such as a temperate winter and be capable of subsequent development to adulthood and/or reproduction. However, this aspect of insect overwintering and cold tolerance has been poorly studied. At high latitudes, Frankliniella occidentalis is typically associated with artificially heated glasshouses, but has some ability to tolerate low temperatures and may survive winter field conditions for short periods, or for longer periods of time during mild winters. The effects of overwintering on the viability of survivors are, however, unknown. In this study, acute and chronic cold exposure regimes were imposed on first instar larvae and adult female Western Flower Thrips, after which the longevity, development and reproductive capacity of the survivors were monitored and compared to those of non-stressed individuals. Survival of cold exposure did not affect subsequent survivorship of immature or adult insects, though cold treated larvae took approximately two days longer to reach adulthood than untreated individuals (at 20°C, 18L:6D). Chill treatment of adult females significantly reduced their rate of reproduction (from 1.45 to 0.93 larvae day^-1), reproductive lifespan (from 13.3 to 9.2 days) and as a result, total reproductive output (from 20.4 to 10.8 larvae), compared to control females. Acute exposure resulted in non-significant decreases of the same parameters. The relevance of the above effects to overwintering of F. occidentalis is discussed.     

Changes in haemolymph parameters and insect ability to respond to immune challenge during overwintering

Overwintering is a challenging period in the life of temperate insects. A limited energy budget characteristic of this period can result in reduced investment in immune system. Here, we investigated selected physiological and immunological parameters in laboratory‐reared and field‐collected harlequin ladybirds (Harmonia axyridis). For laboratory‐reared beetles, we focused on the effects of winter temperature regime (cold, average, or warm winter) on total haemocyte concentration aiming to investigate potential effects of ongoing climate change on immune system in overwintering insects. We recorded strong reduction in haemocyte concentration during winter; however, there were only limited effects of winter temperature regime on changes in haemocyte concentration in the course of overwintering. For field‐collected beetles, we measured additional parameters, specifically: total protein concentration, antimicrobial activity against Escherichia coli, and haemocyte concentration before and after overwintering. The field experiment did not investigate effects of winter temperature, but focused on changes in inducibility of insect immune system during overwintering, that is, measured parameters were compared between naïve beetles and those challenged by Escherichia coli. Haemocyte concentration decreased during overwintering, but only in individuals challenged by Escherichia coli. Prior to overwintering, the challenged beetles had a significantly higher haemocyte concentration compared to naïve beetles, whereas no difference was observed after overwintering. A similar pattern was observed also for antimicrobial activity against Escherichia coli as challenged beetles outperformed naïve beetles before overwintering, but not after winter. In both sexes, total protein concentration increased in the course of overwintering, but females had a significantly higher total protein concentration in their hemolymph compared to males. In general, our results revealed that insect’s ability to respond to an immune challenge is significantly reduced in the course of overwintering.     

The effects of mass and age on standard metabolic rate in house crickets

Abstract. This study employed flow-through respirometry to measure the oxygen consumption rates (VO₂) of inactive male house crickets, Acheta domesticus L. (Orthoptera: Gryllidae), and to quantify the effects of body mass and adult age on standard metabolic rate (SMR). The Vo₂ increased with male body mass at a rate similar to that found in other studies of insect aerobic metabolism. The data reported in this study are combined with published data from other species of Orthoptera to generate a consensus allometric relationship between SMR and body mass for the Order. In general, the Orthoptera expend 2–3 times the energy per unit of body mass when inactive as compared to other arthropods, such as tenebrionid beetles, ants and spiders. Possible explanations for this substantial difference are discussed. By contrast to body mass, mass-specific Vo₂ decreased with increasing male age. This age effect has previously been reported for mammals but is not well established for insects, and its implications for the preference of cricket females for older mates is discussed. As energy expended for metabolic maintenance comprises 78% of a male cricket's daily energy budget, changes in SMR may have a substantial effect on the energy available for reproduction.     

Energy metabolism and metabolic rate of the alder leaf beetle Agelastica alni (L.) (Coleoptera,Chrysomelidae) under aerobic and anaerobic conditions: a microcalorimetric study

In early fall, adult alder leaf beetles (Agelastica alni L.) retreat, for overwintering, to the top layer of the soil near their forage trees where the ground gets easily waterlogged so that the beetles will be submerged and cut off from atmospheric oxygen. Hence, unlike most other adult insects, alder leaf beetles encounter hypoxia/anoxia in their natural habitat and this may occur at moderate temperature. Exposing beetles to pure nitrogen gas at 20 degrees C had similar behavioral and metabolic effects as submerging them in water, causing rapid immobility and increasing the content of lactate about sevenfold to some 5&mgr;molg(-1) body weight during 10h anoxia. Recovery from 10 h hypoxia/anoxia in pure nitrogen was complete within about 90min.Hypoxia/anoxia triggered a marked decrease in metabolic activity in the beetles (microcalorimetry at 21.7 degrees C) as indicated by a precipitous drop in their heat flow rate, from 1.39+/-0.27 to 0.08+/-0.04mWg(-1) body weight, i.e. by about 94%, when the flow of gas through the calorimeter was switched from air to pure nitrogen. Post-anoxic recovery was accompanied by a peak in heat flow rate that exceeded the basal normoxic rate by about 50%. The homoeostasis of adenine nucleotides in Agelastica is lost when oxygen is wanting. Submergence at 15 degrees C for three days caused a dramatic fall in ATP, to less than 2% of the normoxic value, and a marked increase in AMP, while the total contents of adenine nucleotides decreased by almost two-thirds. Reduced metabolic activity, combined with the capacity to regenerate ATP after readmission of air, is regarded as a key factor for surviving transient lack of oxygen in alder leaf beetles.     

The effects of crop microclimate and associated physiological constraints on the seasonal and diurnal distribution patterns of raspberry beetle (Byturus tomentosus) on the host plant Rubus idaeus

Abstract.

• 1 The occurrence of raspberry beetles (Byturus tomentosus) on the host plant Rubus idaeus is extremely variable between seasons, between days and within days, with occupancy of the available raspberry flowers (the feeding and oviposition sites) varying from 0 to 60%.
• 2 This variation could not be explained by plant chemistry or food quality (leaf nitrogen, carbon or water levels, or floral nectar reward); however, beetle distributions were in part attributable to microclimatic constraints acting via the insects’physiological constraints.
• 3 Initial ascent into raspberry canes from soil emergence sites was limited by the three-fold higher water loss rates from recently eclosed young adult beetles as compared with mature beetles. Young adults reduced their hygric stress by remaining in the humid microclimate of tightly furled primocane leaftips.
• 4 Mature beetles spread upwards over the plant, but showed a preference for insolated sites (tops of canes, east or west facing according to time of day). In such sites their body temperatures could rise above the threshold for flight (requiring a T_b of 15°C in laboratory studies). Flight activity was therefore common only in the early afternoon of warm days. Later in the day, beetles moved down and sometimes off the plants, starting to return at around dawn.
• 5 Thus physiological constraints, even on adult beetles (relatively well-protected insect stadia), can be important components in predicting insect movements and locations on a host plant; they are likely to be even more crucial to less highly sclerotized plant-feeding adult insects and many larval herbivorous pests.

     

Management of pine wilt disease vectoring Monochamus alternatus adults using spray and soil application of Metarhizium anisopliae JEF isolates

Chemical control is widely used to control the Japanese pine sawyer beetle, Monochamus alternatus, but strong chemical regulations require an environmentally sound management strategy. In this work, we investigated the use of entomopathogenic fungi and their application as a means of practical pest management. Thirty-two diverse species of fungal isolates were assayed against adult pine sawyer beetles using a contact method under laboratory conditions, and four isolates showed over 70% virulence consequently. These isolates, two each of Beauveria bassiana and Metarhizium anisopliae were sprayed on the adult beetles at 1 × 10⁷ conidia/ml in plastic containers, respectively. The M. anisopliae-treated adult beetles showed 67% mortality. M. anisopliae isolates JEF-197 and JEF-279 demonstrated dosage-dependent insecticidal activity. Following the laboratory experiments, semi-field trials were conducted in young pine trees under high (RH 94%) and low (RH 35%) humidity conditions. In the high humidity conditions, most of the adult beetles stayed on the top of the branches. When the two M. anisopliae isolates were sprayed on the beetles, they showed ca. 50–70% insecticidal activity 11 days after application. In contrast, in low humidity conditions, the adult beetles tried to move off the branches and onto the soil. When the beetles reached the JEF-197 and JEF-279-treated soil, we measured >90% insecticidal activity. This work suggests that M. anisopliae was the most virulent entomopathogenic fungus against adult Japanese pine sawyer beetles, and this forest insect could be ecologically controlled by the spray and soil application of the M. anisopliae isolates.     

Cold tolerance of the montane Sierra leaf beetle,Chrysomela aeneicollis

Small ectothermic animals living at high altitude in temperate latitudes are vulnerable to lethal cold throughout the year. Here we investigated the cold tolerance of the leaf beetle Chrysomela aeneicollis living at high elevation in California’s Sierra Nevada mountains. These insects spend over half their life cycle overwintering, and may therefore be vulnerable to winter cold, and prior studies have demonstrated that survival is reduced by exposure to summertime cold. We identify overwintering microhabitat of this insect, describe cold tolerance strategies in all life stages, and use microclimate data to determine the importance of snow cover and microhabitat buffering for overwinter survival. Cold tolerance varies among life history stages and is typically correlated with microhabitat temperature: cold hardiness is lowest in chill-susceptible larvae, and highest in freeze-tolerant adults. Hemolymph osmolality is higher in quiescent (overwintering) than summer adults, primarily, but not exclusively, due to elevated hemolymph glycerol. In nature, adult beetles overwinter primarily in leaf litter and suffer high mortality if early, unseasonable cold prevents them from entering this refuge. These data suggest that cold tolerance is tightly linked to life stage. Thus, population persistence of montane insects may become problematic as climate becomes more unpredictable and climate change uncouples the phenology of cold tolerance and development from the timing of extreme cold events.     

Long‐term after‐effects of cold exposure in adult Alphitobius diaperinus (Tenebrionidae): the need to link survival ability with subsequent reproductive success

1. The effects of cold acclimation and cold exposure on the survival and reproductive capabilities of Alphitobius diaperinus (Tenebrionidae) adult beetles are examined. 2. First, the impact of temperature on survival duration was assessed by placing beetles in a range of cool temperature treatments. Second, the importance of acclimation duration was assessed. Third, the impact of thermal stress on subsequent reproductive ability was examined for beetles that had no previous cold exposure, and for beetles that had been subjected to previous cold exposure (i.e. acclimated) at various conditions, including fluctuating temperatures. 3. In all groups, the number of recorded survivors was strongly impacted by recovery period duration (i.e. 2 vs. 10 days). Survival of non‐acclimated and 3‐day acclimated beetles, expressed as lethal time for 50% of the samples, was reduced significantly when the insects were re‐assessed for survival at 10 days after being returned to optimal growth conditions (7.9 ± 0.4 vs. 5.1 ± 0.6 days and 8.8 ± 0.5 vs. 6.8 ± 0.6 days, respectively). 4. Insects that had been subject to cold acclimation expressed better subsequent reproduction success than non‐acclimated beetles. This beneficial impact increased when the acclimation period was prolonged, but some longer acclimation periods had no significant impact on survival. 5. Our results indicate that cold exposure has the capacity to irreversibly damage the reproductive system and that insect survival depends on the duration of the recovery period. Both the survival ability and subsequent reproductive output have to be examined to objectively determine insect cold resistance.     

Diving beetle assemblages of flooded wetlands in relation to time,wetland type and Bti-based mosquito control

We investigated the abundance and taxonomic composition of the aquatic predatory insect fauna, with focus on adult diving beetles (Coleoptera: Dytiscidae), in eight temporary flooded wet meadows and two alder swamps in the River Dalälven floodplains, central Sweden from 2002 to 2006. Diving beetles are generalist predators and often abundant in various waters, including temporary wetlands. In the River Dalälven floodplains, recurrent floods induce massive hatching of flood-water mosquitoes (Diptera: Culicidae), which constitute a superabundant patchy and irregular food resource for aquatic predatory insects. Our aims were (1) to characterize the assemblage of adult diving beetles occurring in the wetlands during floods in relation to time and wetland type and (2) to evaluate the effect on the aquatic predator assemblage of strongly reducing the abundance of a potential prey, flood-water mosquito larvae with Bacillus thuringiensis var. israelensis (Bti) during floods. We found diving beetles to be the dominating aquatic predatory insect taxa in all 10 wetlands. There was a difference in Dytiscidae species richness but not in diversity between wet meadows and alder swamps after rarefaction. The cluster analysis based on dytiscid species and abundances showed very high similarities between the wetlands. The variance component analysis was unable to distinguish any factor that could explain more than 7.4% of the variation in the dytiscid species assemblages. The only effect of Bti-treatment against flood-water mosquito larvae, potential food for the predatory dytiscids, was a slight increase in abundance of the medium-sized dytiscid species. Our results are in accordance with previous studies, suggesting that irregular and recurrent flood dynamic structure the dytiscid fauna more than food limitations and environmental factors.     

Improved assay conditions for measurement of corpus allatum activity in vitro in the adult Colorado potato beetle, Leptinotarsa decemlineata

Assay conditions for the short-term, radiochemical, in vitro determination of the spontaneous rate of juvenile biosynthesis by isolated corpora allata from Leptinotarsa decemlineata have been further improved, permitting the measurement of juvenile hormone biosynthesis by individual pairs of corpora allata. The final incubation product has been identified as juvenile hormone III with the aid of High-performance liquid chromatography (HPLC) and juvenile hormone esterase degradation. Using the new assay conditions, the activities of adult corpora allata during maturation were found to be significantly higher in reproductive, long-day animals than in pre-diapause, short-day beetles. During diapause no activity was detectable, whereas corpora allata from post-diapause beetles were reactivated totally after 5 days. Simultaneous determination of the in vitro rates of juvenile hormone biosynthesis and corpus allatum volumes revealed no clear correlation although the results suggest that the volume may be indicative of the maximal capacity for juvenile hormone production. Corpora allata from a population of beetles did not display any synchronous diurnal rhythmicity.     

Global patterns of insect herbivory in gap and understorey environments,and their implications for woody plant carbon storage

Insect herbivory is thought to favour carbon allocation to storage in juveniles of shade‐tolerant trees. This argument assumes that insect herbivory in the understorey is sufficiently intense as to select for storage; however, understoreys might be less attractive to insect herbivores than canopy gaps, because of low resource availability and – at temperate latitudes – low temperatures. Although empirical studies show that shade‐tolerant species in tropical forests do allocate more photosynthate to storage than their light‐demanding associates, the same pattern has not been consistently observed in temperate forests. Does this reflect a latitudinal trend in the relative activity of insect herbivory in gap versus understorey environments? To date there has been no global review of the effect of light environment on insect herbivory in forests. We postulated that if temperature is the primary factor limiting insect herbivory, the effect of gaps on rates of insect herbivory should be more evident in temperate than in tropical forests; due to low growing season temperatures in the oceanic temperate forests of the Southern Hemisphere, the effect of gaps on insect herbivory rates should in turn be stronger there than in the more continental temperate climates of the Northern Hemisphere. We examined global patterns of insect herbivory in gaps versus understories through meta‐analysis of 87 conspecific comparisons of leaf damage in contrasting light environments. Overall, insect herbivory in gaps was significantly higher than in the understorey; insect herbivory was 50% higher in gaps than in understoreys of tropical forests but did not differ significantly between gaps and understories in temperate forests of either hemisphere. Results are consistent with the idea that low resource availability – and not temperature – limits insect herbivore activity in forest understoreys, especially in the tropics, and suggest the selective influence of insect herbivory on late‐successional tree species may have been over‐estimated.     

Factors influencing parasitism of adult Japanese beetles,Polillia japonica (Col.: Scarabaeidae) by entomopathogenic nematodes

Several factors that influence the activity of steinernematid and heterorhabditid nematodes against adult Japanese beetles were examined in the laboratory. The effect of nematode concentration on mortality of adult beetles was evaluated using a Petri plate bioassay. The adults were exposed to 1,000 to 10,000 infective stage juveniles (J3) ofSteinernema glaseri per 10 beetles with or without food for 24 hr after which they were held with food for an additional 6 days. The LC50s for males with and without food during exposure were 3,435 and 2,854 J3s/10 adults, respectively. The LC50s for mixtures of males and females with and without food were 5,228 and 1,762 J3s/10 adults respectively. Although mortality occurred during and shortly after exposure, significant additional mortality was observed 1–4 days following exposure. Exposure of males and females with food to 10,000 J3s/10 adults for 6, 12, 18 or 24 hr resulted in 47, 58, 72 and 77% mortality, respectively. Comparative activity ofS. glaseri, S. carpocapsae (All strain),S. feltiae (Biosys experimental cold adapted strain=bibionis),S. feltiae (Biosys experimental strain 27),Heterorhabditis bacteriophora, andHeterorhabditis sp. (Terceiran isolate) was evaluated against adult Japanese beetles using a 24 hr exposure to 8,000 J3s/10 adults. The most virulent species wereS. glaseri, S. feltiae (=bibionis), the Terceiran isolate ofHeterorhabditis andS. carpocapsae producing 55, 44, 36 and 34% mortality respectively. Our results indicate that adult Japanese beetles infected with entomopathogenic nematodes could serve as a mechanism for nematode dispersal.     

Life at a different pace: Annual itineraries are conserved in seasonal songbirds

The duration of life history state (LHS) reflects the adaptive strategy a species has evolved to cope with a changing environment. Inhabitants at different latitudes may thus have significant differences in the rates of metabolic and physiological processes underlying LHSs. Birds, in order to maximize their fitness in the environment in which they live, seasonally switch from one LHS to another during the year. The present study investigated whether an annual itinerary of a species would determine its rate of reaction to inductive long days. We compared the photoinduced cycles of changes in body mass and testes, as indices of migratory and reproductive LHSs, between two long day breeding species, the migratory redheaded bunting and non-migratory Indian weaverbird. Changes in body mass and testis size were measured in photosensitive buntings and weaverbirds (n = 7 each) on short days (LD 8:16) subjected first to 0.5 h weekly light increments until the light period was 13 h per day, and then maintained on LD 13:11 for another 32 weeks. A similar observation was recorded on a group of buntings (n = 14) and weaverbirds (n = 9) maintained on increasing natural day lengths (NDL; Lucknow, 26°55' N, 80°59' E) for 47 weeks. As predicted, the rates of induction of seasonal cycles under an identical inductive photoperiod were significantly faster in temperate buntings with five annual LHSs than in the subtropical weaverbirds with three annual LHSs. This suggests that annual itineraries of songbirds with which they may have evolved with at their breeding latitudes, determine their response to the external photoperiodic environment.     

Delaying insect access alters community composition on small carrion: a quantitative approach

We present a study of interactions in the highly competitive insect communities inhabiting the carrion of small mammals. Via manipulation in a fully quantitative design, we delayed community development by excluding insect colonization in mouse and rat carcasses for 3 days, to study the role of early competitively dominant colonizers [burying beetles (Nicrophorus spp.; Coleoptera: Silphidae) and blowfly larvae (Diptera: Calliphoridae)] in the course of heterotrophic succession on small cadavers. Earlier studies demonstrated that in the case of large mammalian carrion, exclusion of insects’ access to the carcass in the early stages of decomposition altered the successional trajectory and species assemblages. However, the effect of such manipulation in easy monopolizable small vertebrate carrion remained unknown. Our results demonstrate that delaying insect access to carrion significantly lowered blowfly larvae abundances, while it simultaneously had no effect on colonization and carrion burial by burying beetles. Higher abundances of blowfly larvae seem to deter necrophagous beetles, whereas they are not harmful to the larvae of flesh flies, at least in larger rat carcasses. Predatory beetle species preferred the lower abundances of blowfly larvae, presumably due to better accessibility of their prey. Our results therefore suggest that in the course of the entire season, larvae of blowflies are the dominant competitors in small carcasses, and significantly affect the assembly of other insect groups, whereas burying beetles may exhibit a more temporal pattern of dominance.     

PHYLOGENESIS OF INSECT/PLANT INTERACTIONS: HAVE PHYLLOBROTICA LEAF BEETLES (CHRYSOMELIDAE) AND THE LAMIALES DIVERSIFIED IN PARALLEL?

The relative importance of conservative versus locally adapted traits for species interactions is an increasingly common theme in evolutionary ecology. Obligate interactions such as those between parasites and hosts often exhibit such strong phylogenetic conservatism that current associations may reflect diversification in parallel. Parallel phylogenesis, documented for animal parasites, has been doubted for insect/plant interactions, but phylogenetic studies of highly specific insect/plant associations are very few. A comparison of phylogeny estimates for the strictly monophagous Phyllobrotica leaf beetles and their lamialean hostplants shows nearly complete concordance, strongly supporting the hypothesis of parallel diversification. The cladogram concordance is significant or nearly so (consensus index values equalling or exceeding the critical value) under randomization distributions based on Adams (though not Nelson) consensus trees. The one clear exception shows unusual natural history, suggesting an isolated host transfer. Insect distributions and plant fossil ages are consistent with a mid-Tertiary age for both clades, further disfavoring the alternative hypothesis of entirely subsequent evolution. The dependence of both larval and adult beetles on the hostplants, larval endophagy, and possible dependence of beetles on toxic host compounds for defense against predators are suggested to underlie the evolutionary persistence of this interaction. Current host use in these beetles appears to reflect primarily the phylogeny of the interaction, strengthening the thesis that history can play a major role in structuring insect/plant relationships.     

Some observations on photoperiodism and the development of annual forms of domesticated cottons

Observations made over the last fifteen to twenty years have discovered no primitive forms of G.barbadense L. orG. hirsutum L. (other than G.hirsutum racelatifolium Hutchinson) which are capable of flowering during the long summer days of temperate latitudes. Annual Upland cottons, grown in the southern United States since the mid-eighteenth century, were probably derived from perennial day-neutral forms of Mexican racelatifolium, though not necessarily by direct introduction from Mexico into the United States. The origin of Sea Island cottons (day-neutral forms of G.barbadense), which were formerly grown on the southeastern seaboard of the United States since the mid-eighteenth century, remains obscure. No primitive forms of this species, capable of flowering during the long summer days of temperate latitudes, have been found. An experiment is reported in which it has been possible to synthesize a day-neutral form of G.barbadense through introgression between primitive short-day sensitive forms of G.barbadense and G.hirsutum, both native to the Caribbean region. It is suggested that the ancestors of Sea Island cottons may have originated naturally by a similar mechanism involving the same species.