Biology, life table and predation of Feltiella acarisuga (Diptera: Cecidomyiidae) feeding on Tetranychus cinnabarinus eggs (Acari: Tetranychidae)

Feltiella acarisuga (Vallot) is a common predatory gall midge, which feeds on many species of spider mites. All major life history and life table parameters of F. acarisuga were determined using the carmine spider mite, Tetranychus cinnabarinus (Boisduval) eggs as prey under laboratory conditions [26.7 ± 2 °C, 75 ± 5% RH, and a photoperiod of l4:10 (L:D) h]. Developmental times of F. acarisuga were 2.6, 7.1, and 6.7 d for eggs, larvae, and pupae, respectively, with an average of 16.4 d from egg to adult emergence. Female immatures development took ≈1 d longer than male immatures did. Adult F. acarisuga lived an average of 12.8 d, and the female adults (13.3 d) lived significantly longer than male adults did (11.9 d). After an average of 1.5 d preoviposition period, each female laid an average of 27.3 eggs in its life span with an average of 2.1 eggs per day and an average of 2.8 eggs on each of its oviposition day. The raw data were analyzed using an age-stage, two-sex life table method that takes into consideration of the variable developmental rates among individuals and between sexes. The intrinsic rate of natural population increase (r), net reproductive rates (R_o), gross reproductive rate (∑m_x), generation time (T), and doubling time (DT), and the finite rate of increase (λ) of F. acarisuga were estimated using the age-stage, two-sex (male and female) life table analysis as 0.122 d⁻¹, 16.19 eggs per female, 20.81 eggs per female, 22.81 d, 1.1298 d, and 5.7 d⁻¹, respectively. Each of the first, second, and third instar larvae of F. acarisuga consumed an average of 35.5, 54.0 and 86.9 T. cinnabarinus eggs per day, respectively. Larvae of F. acarisuga could consume an average of 175.4, T. cinnabarinus eggs, and female larvae consumed 14% more spider mite eggs (187.6 eggs) than male larvae (165.1 eggs). The significance of other life table parameters related to the population and the potential of using F. acarisuga as a biological control agent are discussed.     

Egg Deposition Behavior in the Haplodiploid Sawfly Athalia rosae ruficornis Jakovlev (Hymenoptera: Symphyta: Tenthredinidae)

The egg deposition behavior of the turnip sawfly, Athalia rosae (Hymenoptera: Symphyta), is described. Both unmated and mated females lay eggs individually inside of fresh young leaves of cruciferous plants. During an oviposition event, females exhibit a distinct pause in abdominal contractions just before the actual egg deposition act. Unmated females show a longer pause (11.31 s on average) than mated females (4.38 s on overall average). By employing an eye color mutation, the sex of the eggs laid by females was ascertained. Females mated once lay mostly fertilized (diploid female) eggs initially but begin to lay a considerable number of unfertilized (haploid male) eggs later in life. The laying of an unfertilized egg is associated with a longer pause (6.98 s on average) than the laying of a fertilized egg (3.76 s on average). These results are in contrast to previous reports on apocritan Hymenoptera, where the presence of a pause or a longer pause during oviposition was associated with the deposition of fertilized eggs rather than unfertilized eggs. The possibility that mated Athalia rosae females control fertilization and its implications for sex allocation strategies are discussed.     

Life history and demography of the predatory mite,Amblyseius longispinosus Evans

The life history and demography of Amblyseius longispinosus Evans were studied under laboratory conditions 25–28°C and 65–85% RH using the red form of the twospotted spider mite, Tetranychus urticae Koch complex as prey. The entire development from egg to adult averaged 102.5 h for both sexes with a survival rate of 90.0%. Immature females consumed more prey eggs than males, averaging 7.9 and 6.4 eggs/day, respectively. The embryonic development time for male eggs was longer (average 45.2 h) than for female eggs (average 42.6 h). The average duration of succeeding stages did not differ between the sexes: larva, 15.7; protonymph, 21.1; and deutonymph, 23.0 h. Larvae were not observed to feed. Statistically significant differences between sexes were noted with respect to consumption of the deutonymphs (female, average 4.0±0.2; male, average 2.9±0.3 eggs/day) but not of the protonymphs. Mating occurred on the same day as adult emergence and was repeated several times during the reproductive life. Egg laying started on the second day after emergence. Parameters relating to oviposition were: fecundity, gross (50.7) and net (43.3) eggs/female; hatchability, 99.6% (gross) and 99.5% (net); the oviposition lasted at most 28 days and showed a peak in the first week. Net reproductive rate (R₀) was 36.7 female offspring/female/generation time (T) of 9.0 days. The sex ratio was biased toward the females (71.9%), while the intrinsic rate of increase (r_m) was 0.4 with a doubling time (DT) of 1.7 days. Males lived longer (36 days) than females (30 days) with a LT₅₀ for males of 26 days and for females of 22 days.     

The Predatory Mite Phytoseiulus persimilis Adjusts Patch-leaving to Own and Progeny Prey Needs

Integration of optimal foraging and optimal oviposition theories suggests that predator females should adjust patch leaving to own and progeny prey needs to maximize current and future reproductive success. We tested this hypothesis in the predatory mite Phytoseiulus persimilis and its patchily distributed prey, the two-spotted spider mite Tetranychus urticae. In three separate experiments we assessed (1) the minimum number of prey needed to complete juvenile development, (2) the minimum number of prey needed to produce an egg, and (3) the ratio between eggs laid and spider mites left when a gravid P. persimilis female leaves a patch. Experiments (1) and (2) were the pre-requirements to assess the fitness costs associated with staying or leaving a prey patch. Immature P. persimilis needed at least 7 and on average 14±3.6 (SD) T. urticae eggs to reach adulthood. Gravid females needed at least 5 and on average 8.5±3.1 (SD) T. urticae eggs to produce an egg. Most females left the initial patch before spider mite extinction, leaving prey for progeny to develop to adulthood. Females placed in a low density patch left 5.6±6.1 (SD) eggs per egg laid, whereas those placed in a high density patch left 15.8±13.7 (SD) eggs per egg laid. The three experiments in concert suggest that gravid P. persimilis females are able to balance the trade off between optimal foraging and optimal oviposition and adjust patch-leaving to own and progeny prey needs.     

Effects of temperature and soil moisture on survival of eggs of the mosquito Psorophora columbiae (Diptera: Culicidae)

The results of laboratory tests indicated the average survival rates for Psorophora columbiae eggs remained quite high for all of the egg populations exposed to a temperature of 27°C (range 83.0–100.0% survival) after 96 days of exposure, except for the non‐diapausing eggs on dry soil (66.3%). In regard to the exposure of egg populations to moderately cold temperatures (i.e. 8°C, 4°C and ?2°C) for periods of up to 16 days, survival rates for egg populations exposed to 8°C continued to remain relatively high (average >85%) for the remainder of the experimental exposure period (i.e. 96 days). Diapausing Ps. columbiae eggs were more tolerant (82.0% survival) to low temperatures (?2°C) than non‐diapausing eggs (2.4% survival) for 64 days, particularly at temperatures of and below 4°C. Diapausing and non‐diapausing eggs were similar in their ability to survive under high temperatures (34°C and 38°C). High soil moisture (30–40%) or substrate moisture (95% relative humidity) content appeared to enhance the ability of the mosquito eggs to survive both low and high temperature extremes.     

Agistemus exsertus Gonzalez (Acari: Stigmaeidae) as a predator of two scale insects of the family Diaspididae (Homoptera: Diaspididae)

Abstract

The predacious mite Agistemus exsertus Gonzalez completed its life-span when fed on eggs and crawlers of the Florida red scale Chrysomphalus ficus Ashmead and the white date scale Parlatoria blanchardi (Targioni). The development was faster when individuals were maintained on eggs and crawlers of C. ficus, compared with both stages of P. blanchardi. The average number of eggs/female/day was 2.5 and 1.1 on eggs and crawlers of C. ficus, respectively. Eggs and crawlers of P. blanchardi were an unsuitable food for egg laying for A. exsertus. Life table parameters showed that A. exsertus preferred eggs of C. ficus to the crawlers as prey. The population of the predator feeding on eggs and crawlers of Florida red scale multiplied 45 and 7 times in a generation time of 23 and 20.5 days, respectively. Under these conditions, the intrinsic rate of increase (r _m) was (0.17 and 0.098) individuals/female/day on eggs and crawlers of C. ficus, while the finite rate of increase (λ) was (1.18 and 1.11) on both stages of C. ficus.     

Biology and host specificity of <Emphasis Type="Italic">Gonatocerus deleoni</Emphasis> (Hymenoptera: Mymaridae), a potential biocontrol agent of <Emphasis Type="Italic">Homalodisca vitripennis</Emphasis> (Hemiptera: Cicadellidae) in California,USA

The host-specificity and biological traits of Gonatocerus deleoni Triapitsyn, Logarzo & Virla (Hymenoptera: Mymaridae), a potential candidate for biological control of the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), were determined under laboratory conditions. G. deleoni is a solitary egg parasitoid native to Argentina, originally reared from sentinel eggs of Tapajosa rubromarginata (Signoret) (Cicadellidae). With GWSS as a fictitious host, G. deleoni’s average development time from oviposition to adult emergence was 18.8 ± 1.4 days, with males developing faster than females (18.0 ± 1.3 days, males; 19.0 ± 1.3 days, females). The average parasitism rate on 1–8-day-old eggs was 45.7% but this was significantly affected by the age of the egg, ranging from 1.4% to 69.9% (egg ages 8 and 3, respectively). The average sex ratio was 0.34 (percent males) and sex ratio was not significantly affected by egg age. G. deleoni was able to develop in eggs of GWSS and Homalodisca liturata Ball (both in the tribe Proconiini), but was unable to develop on eggs of Graphocephala atropunctata (Signoret) (different tribe, same subfamily) or Erythroneura elegantula Osborn (different subfamily).     

Amino acid cues emanating from Pacific salmon eggs and ovarian fluid

The eggs of salmonid fishes are an important food source for many aquatic predators that detect eggs using olfaction. Moreover, chemicals from eggs and ovarian fluid aid sperm cells in detecting and locating eggs for fertilization, and ovarian fluid is attractive to conspecific males. Thus chemicals from eggs and ovarian fluid may facilitate reproduction but may also attract egg predators. The authors sampled mature females of three Pacific salmon species – Chinook (Oncorhynchus tshawytscha), coho (Oncorhynchus kisutch) and sockeye (Oncorhynchus nerka) – and determined the proportional representation of amino acids, potent fish odorants, from their eggs and ovarian fluid (Chinook and coho salmon only). They then tested juvenile coho salmon, an egg predator, for responses to ovarian fluid and egg odours using the electro-olfactogram (EOG) recording technique. The amino acid compositions of the salmon species were significantly and positively correlated with each other, and the interspecific differences were comparable to those between individuals of the same species. The egg water samples were, on average, dominated by lysine, alanine and glutamine (12.6%, 12.4% and 10.9%, respectively). The ovarian fluid samples were dominated by lysine (20.5%), followed by threonine (9.7%), glycine (9.2%) and arginine (8.8%). EOG recordings demonstrated the ability of juvenile coho salmon to detect the chemical traces of eggs and ovarian fluid. It is concluded that salmon eggs are a potent source of odours for potential predators but likely not highly differentiated among salmon species.     

Implications of resting eggs of zooplankton for the paradox of enrichment

In this study, we numerically investigated to what extent introducing resting-egg dynamics would stabilize simple Daphnia–algae consumer–resource models. In the models, the density of viable resting eggs was explicitly expressed, and we assumed that zooplankton produced resting eggs seasonally or in response to food deficiency and that resting eggs hatched seasonally. The models predicted that, although the paradox of enrichment was not completely resolved (i.e., the system was destabilized by eutrophication), we found the following conditions under which the stabilizing effects of resting eggs would be significantly large: (1) resting eggs are produced seasonally (rather than in response to food deficiency), (2) the annual average allocation ratio to resting eggs is large, and (3) the annual average hatching rate of resting eggs is low. The results suggest that resting-egg dynamics can significantly reduce the paradox of enrichment within the biologically meaningful parameter space and contribute to the stability of plankton community dynamics.     

Predation of Clitostethus arcuatus (Col.: Coccinellidae) on Trialeurodes vaporariorum (Hem.: Aleyrodidae)

Greenhouse whitefly, Trialeurodes vaporariorum, is a serious pest of glasshouse crops. It shows resistance to different insecticides and growers are interested in finding other useful control methods. This research was carried out to study the predation potential and biology of Clitostethus arcuatus (Rossi) as one of the most important predators of this pest. Adult C. arcuatus were reared on tobacco leaves bearing colonies of greenhouse whitefly eggs under controlled conditions (25±2°C, 65±5% RH and 16 h L:8 h D). Results showed that the average developmental time of the egg, first through fourth instar larva and pupa were 2.82±0.12, 4.47±0.14, 4.54±0.1, 6.3±0.2, 7±0.22 and 3.8±0.13 days, respectively; and longevity of female and male were 66.4±2.6 and 54.9±2.5 days, respectively. The average feeding rates of female, male and larvae (first through fourth) were 61.4±0.7, 27.6±0.9 eggs/day and 12±1.03, 30.3±2.4, 41.3±2, 68.04±2 eggs/day, respectively. The larvae consumed an average of 992.2±36 eggs during the total larval developmental period with a daily mean of 45.8±0.5. A significant difference was shown between the feeding rate of fourth instar larval stages and between sexes. Females, males and one pair of C. arcuatus (♀,♂) consumed an average of 17.2±0.4, 10.6±0.8, 23.1±0.5 nymph/day; 28.5±0.9, 20.3±0.6, 47.2±0.6 pupa/day and 8±0.3, 6.5±0.54, 13.6±0.4 adult/day, respectively. The feeding rate was significantly different among whitefly life stages. Females laid an average of 3±0.23 eggs/day.     

Temperature effects on reproduction and adult lifespan of the smaller fruit tortrix,Grapholita lobarzewskii

The effects of temperature on adult lifespan, reproduction, and oviposition behaviour of Grapholita lobarzewskii Nowicki (Lepidoptera: Tortricidae) were studied under controlled and semi‐field conditions to improve the basis for phenological forecasting. The average female lifespan ranged from 18.9 days at 25.1 °C to 65.3 days at 11.0 °C. For adult female ageing, a lower thermal threshold (THR) of 8.6 °C and a thermal constant (K) of 298 degree days (dd) were established. At constant temperatures, fecundity ranged from 0.3 eggs per female at 11.0 °C to 107 eggs per female at 21.2 °C. The highest fecundity of 127 eggs per female was observed at fluctuating temperatures. Oviposition lasted on average 350 dd, but 50% of the eggs were laid within the first 100 dd after adult emergence. Grapholita lobarzewskii had a distinct circadian rhythm for oviposition. Females began to lay eggs at ca. 16:00 hours and ceased at 24:00 hours with the peak occurring generally at 19:00 hours. Females reacted very sensitively to sudden temperature changes. A temperature drop of 3.1 °C could cause a 1‐day interruption of oviposition.     

Seasonal patterns of egg production in field colonies of the termite <Emphasis Type="Italic">Reticulitermes speratus</Emphasis> (Isoptera: Rhinotermitidae)

This is the first report on the annual egg production patterns in mature termite colonies in the field. Data on the seasonal patterns of egg production in field colonies are very important for understanding the annual colony growth schedule, resource allocation, and population dynamics of the termites. However, collecting the eggs from a sufficient number of colonies is extremely difficult in Reticulitermes termites because their multiple-site nesting makes it difficult to find the reproductive center of the colonies. Here, we first show the seasonal pattern of egg production in the subterranean termite Reticulitermes speratus by collecting the reproductive center of ten colonies each month from April through October. We had to destructively examine dozens of nests to find eggs from enough field colonies each month. Mature field colonies began to produce eggs in late May, soon after the swarming season, and the egg production rate (EPR) reached its maximum in early July. The eggs hatched until late October. The EPR was significantly correlated with the average monthly temperature. Additional investigation of the egg distributions in the nests showed that most eggs were kept around the royal cell, which contained the reproductives. The largest colony had 109 supplemental queens and 94,023 eggs, suggesting that each queen produced an average of 24.7 eggs per day, based on the known mean hatching period of an inseminated egg of 34.95±0.12 (SE) days.     

Laboratory and field tests of predation on the cereal leaf beetle,Oulema melanopus (Coleoptera: Chrysomelidae)

The cereal leaf beetle (CLB), Oulema melanopus (L.) (Coleoptera: Chrysomelidae), is an invasive pest in North America recently reported in the Canadian Prairies. We performed a series of laboratory assays to identify potential predators and a field study to quantify predation of CLB eggs. In no-choice Petri dish assays, ground beetles (Carabidae), rove beetles (Staphylinidae), and several common lady beetle species (Coccinellidae) were the most consistent predators of eggs and larvae. Nabis spp. (Hemiptera: Nabidae) and wolf spiders (Araneae: Lycosidae) consumed many larvae, but did not consume eggs. Hippodamia spp., Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), and Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) also fed on CLB eggs on potted plants when an alternative food source was available, Sitobion avenae (Fabricius) (Hemiptera: Aphididae). In our field study, we found an average of 24.5% of sentinel eggs disappeared over a 24?h period, likely due to predation. Our results suggest that generalist predators can play an important role in the biological control of CLB, and warrant further study.     

Life table and predation of Oligota pygmaea (Coleoptera: Staphylinidae) a major predator of the red spider mite, Oligonychus coffeae (Acarina: Tetranychidae) infesting tea

The staphylinid beetle, Oligota pygmaea (Solier) is an important predator of the red spider mite, Oligonychus coffeae (Nietner) infesting tea. Biology, life table and predatory efficiency of O. pygmaea were studied under laboratory conditions. Duration of developmental stages of O. pygmaea was 3.2, 5.7 and 12.5 d for eggs, larvae and pupae, respectively with an average of 23.0 d from egg to adult emergence. After a mean preovipostion period of 2.9 d, each female laid an average of 400.5 eggs in its life span. Adult O. pygmaea lived for an average of 54.1 d. Adult females lived for a longer period of 58.8 d compared to the longevity of 49.4 d of adult male. Studies revealed that its life table characterized by an intrinsic rate of natural population increase (r) of 0.118 d, net reproductive rates (R_o) of 243.693 eggs/female, gross reproduction rate (Σm_x) of 245.313 eggs/female, generation time (T) of 46.575 d, doubling time (DT) of 5.874 d and finite rate of increase (λ) of 1.125 d. Seasonal abundance of O. pygmaea and its prey, O. coffeae was monitored by sampling 25 tea leaves randomly from each experimental block grown under the prevailing field conditions. O. pygmaea showed a typical pattern of population dynamics with a peak during January to March and low incidence during June to September. Peak in the population of O. pygmaea coincided with the abundance of O. coffeae in the tea fields. Weather factors such as high temperature, low relative humidity and low sunshine hours adversely affected the populations of O. pygmaea. The first to third instar larvae of O. pygmaea consumed 31.0–133.2 eggs of mites per day. Third instar larva of O. pygmaea consumed an average of 133.2 eggs, 46.4 hexapod larvae, 39.6 nymphs and 11.4 adults per day. Adult females consumed more number of red spider mites compared to the males.     

Influence of pesticide treatments on consumption ofTetranychus urticae [Acarina: Tetranychidae] eggs byPhytoseiulus persimilis [Acarina: Phytoseiidae]

Choice and no-choice experiments were conducted on lima bean leaf discs to determine whether pesticide or water treatments would affect consumption ofTetranychus urticae Koch eggs byPhytoseiulus persimilis Athias-Henriot. In choice experiments,P. persimilis consumed significantly more untreated eggs than eggs treated with fenbutatin-oxide (600 ppm), cyhexatin (200 ppm), or water, when tested at 24, 48, or 72 h after treatment. The surfactant Triton X-100 was included in each pesticide suspension and the water-treated control at 0.1%. On the average, treated eggs amounted to only 30% of the total consumed (n=1,440). The water-treatment effect was weaker than the acaracides at 24 h, but effects did not differ at 48 and 72 h. In 24 h no-choice experiments,P. persimilis consumed as many eggs treated with fenbutatin-oxide, cyhexatin, water, or insecticidal soap (7 575 ppm) as untreated eggs. Fluvalinate treatment of prey eggs (89 ppm), however, resulted in a 50% reduction in egg consumption among predators remaining on leaf discs and a 6-fold increase in abandonment of discs as compared with the untreated control. Continuous consumption of fenbutatin-oxide-treated eggs over 5d did not affectP. persimilis oviposition or egg viability.      

Macrolophus caliginosus: Functional response to whiteflies and preference and switching capacity between whiteflies and spider mites

Laboratory experiments were performed with adult female Macrolophus caliginosus Wagner (Heteroptera: Miridae) at 22ºC on bean plants to determine the functional response towards whiteflies, as well as the preference and switching capacity between the two prey species: whiteflies and spider mites. Predation of females presented with first instars of Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) was of a Type III functional response. The observed maximum predation was approximately 75 first instars at high prey densities within a 24-h period. The preference of M. caliginosus females between eggs of T. vaporariorum and Tetranychus urticaeKoch (Acarina: Tetranychidae) changed with the ratio of offered prey. The preference for T. vaporariorum eggs increased non-linearly with increasing proportions of this prey type. The average maximum predation of whitefly and spider mite eggs were approximately 166 and 111 eggs per day, respectively, at the highest ratio of the two preys. The proportion of M. caliginosus females found on the test plants at the end of the experiment increased with prey density suggesting that this mirid spends more time in areas with high prey density. Macrolophus caliginosus females are voracious predators of eggs and first instars of T. vaporariorum as well as of spider mite eggs and may thus be a valuable addition to existing methods of biological control of T. vaporariorum and T. urticae.     

Resistance to freezing temperatures in Aedes (Ochlerotatus) albifasciatus (Macquart) eggs (Diptera: Culicidae) from two different climatic regions of Argentina

Aedes (Ochlerotatus) albifasciatus (Macquart) has the capacity to proliferate in different kinds of climates within its distribution range in South America. With the aim of studying local thermal adaptations of eggs, we exposed egg stocks from two climatically different localities: temperate humid pampa (Buenos Aires) and cold arid Patagonian (Sarmiento), to freezing conditions and then evaluated the effect on some features at this level. First, we thermally described the substrate where this species lays its eggs in the arid region. A typical thermal condition during winter was 10 h at ?12° C. Second, we evaluated the effect of freezing on primary hatching (vs total hatching) and embryo survival. We also compared the proportion of embryonated eggs from both populations. The proportions of embryonated eggs were not different between localities, with averages of 78% and 83% in Sarmiento and Buenos Aires, respectively. Survival was equally successful after freezing in the two localities with an average range between 94–99%. Whether or not the eggs from Buenos Aires and Sarmiento were under freezing conditions, hatching was more than 98% after the first flooding. The results suggest that eggs of Ae. albifasciatus from Sarmiento and Buenos Aires have the same ability to survive at extreme temperatures (<0° C), showing a regional thermal adaptation rather than a local one.     

广聚萤叶甲成虫产卵行为及其产卵部位的选择性

【目的】明确广聚萤叶甲成虫产卵行为及其产卵部位的选择性。【方法】在室内条件下,对广聚萤叶甲成虫交配及产卵的系列行为、产卵场所选择、不同部位豚草植株叶片叶绿素b的含量进行了观察和测定:(1)将1对成虫放到养虫笼内的一株豚草上,观察交配时间,记录产卵数量、前后2粒卵之间的产卵时间间隔;(2)在均匀分为5部分(0～10、11～20、21～30、31～40和41～50 cm)的豚草植株上,随机放置10对成虫,观察雌虫对于产卵场所的选择。(3)将上述5个部位的豚草叶片通过丙酮匀浆法处理,用紫外分光光度计测定其在645和663 nm的吸光值,计算叶绿素b含量。【结果】广聚萤叶甲成虫完成一次成功交配平均需96.09 min。雌虫一般需45 min的时间来寻找其适应的产卵场所,在产卵过程中,成虫习惯将卵产于叶片背面,雌虫喜欢用口器来清理刚产下的卵粒。在一株50 cm高的豚草植株上,雌虫喜欢将卵产在植株中部21～30 cm和中上部31～40cm的叶片上(从下往上划分)。卵块数量和豚草不同部位叶片叶绿素b含量呈显著的正相关性。【结论】广聚萤叶甲成虫喜欢产卵在叶绿素b含量较高的叶片背面,可能以视觉识别叶片颜色来选择和定位产卵场所。     

Seed beetle survivorship,growth and egg size plasticity in a paloverde hybrid zone

1. Although numerous studies have examined the ecology of plant resistance to herbivores and the distribution of herbivores within plant hybrid zones, few have examined how plant hybridization influences herbivore growth, development, or life history. The experiment reported here examines variation in survivorship, development time, and final adult body size of Stator limbatus reared on seeds of parental and hybrid Cercidium floridum-×-C. microphyllum trees from a paloverde hybrid zone in eastern California. Because S. limbatus exhibits egg size plasticity in response to host species, the size of eggs that females lay on hybrid and parental plants is also examined. 2. The hypotheses (a) that seeds of hybrid trees are intermediate between those of the two parental species in their resistance to penetration by S. limbatus larvae; (b) that seeds of hybrid trees are intermediate in their suitability for the growth of larvae that successfully penetrate the seed-coat; (c) that female S. limbatus can distinguish between hybrid trees and pure-bred trees, as quantified by the size of eggs they lay on seeds of each taxon, and (d) that female S. limbatus can distinguish among individual hybrid trees, are tested. 3. On average, S. limbatus survivorship was lower, development time longer, and emergence body mass lower on seeds of C. floridum than on seeds of C. microphyllum. Seeds of hybrid trees were, on average (across trees), intermediate between seeds of the parental species in the resistance of their seed-coats to penetration by S. limbatus larvae and in their suitability for larval growth. Individual hybrid trees also varied in the resistance of their seeds to, and the suitability of their seeds for, S. limbatus larvae. 4. Female S. limbatus laid significantly larger eggs on seeds of C. floridum than on seeds of C. microphyllum, and, on average, intermediate size eggs on hybrid trees. The size of eggs laid by females also varied among hybrid trees, with females laying C. floridum-sized eggs on some trees, and C. microphyllum-sized eggs on other trees. These results suggest that females have at least some ability to distinguish among hybrid trees, but there was no evidence that females laid larger eggs on poorer quality hybrid trees.     

Reproductive strategy,spawning induction,spawning temperatures and early life history of captive sicklefin chub Macrhybopsis meeki

Macrhybopsis reproduction and propagule traits were studied in the laboratory using two temperature regimes and three hormone treatments to determine which methods produced the most spawns. Only sicklefin chub Macrhybopsis meeki spawned successfully although sturgeon chub Macrhybopsis gelida released unfertilized eggs. All temperature and hormone treatments produced M. meeki spawns, but two treatments had similar success rates at 44 and 43%, consisting of a constant daily temperature with no hormone added, or daily temperature fluctuations with hormone added to the water. Spawns consisted of multiple successful demersal circular swimming spawning embraces interspersed with circular swims without embraces. The most spawns observed for one female was four and on average, 327 eggs were collected after each spawn. The water‐hardened eggs were semi‐buoyant and non‐adhesive, the first confirmation of this type of reproductive guild in the Missouri River Macrhybopsis sp. From spawn, larvae swam vertically until 123 accumulated degree days (° D) and 167° D for consumption of first food. Using average water speed and laboratory development time, the predicted drift distance for eggs and larvae could be 468–592 km in the lower Missouri River. Results from this study determined the reproductive biology and early life history of Macrhybopsis spp. and provided insight into their population dynamics in the Missouri River.