Rostrum structure and development in the rice weevil Sitophilus oryzae (Coleoptera: Curculionoidea: Dryophthoridae)

A documentation and review of weevil rostrum growth is made through examination of the developmental life stages in the rice weevil Sitophilus oryzae (Linnaeus). Histological and morphological examinations are made utilizing light, fluorescent, and electron microscopy. In S. oryzae, rostral tissue begins proliferating in the late 4th instar larva and continues through to the pupal stage, with the majority of rostrum growth taking place in the prepupa. Adult cranial and rostral morphology is also reviewed, focusing on structures that may be pertinent to phylogeny reconstruction. The weevil rostrum is essentially an extension of various head sclerites that are basal to the mouthparts. Therefore, while the mouthparts are fairly similar to other Coleoptera in basic form, the head is markedly different due to its anterior extension. By understanding the more noticeable details of rostrum growth and structure, this study may serve as a foundation for comparative studies of a similar nature and as a basis for beginning research on the genetic nature of rostrum formation and evolution throughout the weevil clade.     

On birth and death in the sea

We present the first comparative study of the stage-specific patterns of mortality of Calanus and Pseudocalanus, two widely distributed genera that are representative of a relatively large-bodied, broadcast spawning calanoid copepod and a relatively small-bodied, egg-brooding calanoid. The study site is Georges Bank, a continental shelf locality in the Northwestern Atlantic with retentive circulation that renders it suitable for studies of population dynamics. Based on extensive mortality estimates from 30 cruises, we find that co-occurring Calanus finmarchicus and Pseudocalanus spp. have markedly different patterns of stage-specific mortality, the former bimodal and the latter relatively uniform with respect to developmental stage. Neither taxon exhibits a monotonic decline in mortality with developmental stage, nor are rates of mortality predictable in a useful manner by copepod body size or by ambient temperature. Young stages of the broadcast-spawning C. finmarchicus show conditional density-dependence of mortality rates, i.e. mortality rates are independent of population density when adult females are low in abundance but positively related to population density at high female abundances. This density-dependence, which is probably attributable to egg cannibalism, introduces a quadratic mortality term into population dynamic models. The egg-brooding Pseudocalanus spp., in contrast, show no evidence of density-dependent mortality. The two taxa illustrate a life history trade-off: the broadcast-spawning Calanus exhibits birth rates that are greatly elevated with respect to those of Pseudocalanus, but there is a compensatory cost in very low survivorship of the freely spawned eggs. Both the high fecundity, high mortality life history of Calanus and the low fecundity, low mortality life history of Pseudocalanus appear to have approximately equal fitness in this study site.     

Susceptibility of various developmental stages of the maize weevil, Sitophilus zeamais Motschulsky (Col., Curculionidae) to methyl iodide in brown rice

Abstract:  The efficacy of methyl iodide (MI) as a fumigant against all developmental stages of the maize weevil, Sitophilus zeamais Motsch. was investigated. Tests were conducted with concentrations of 1.5, 1.8, 2.1, 2.4, 2.7 and 3.0 mg/l, for a 6-h exposure period. Values of LC₅₀, LC₉₅ and LC₉₉ of MI for immatures and adult stages were determined. The present laboratory tests showed that MI was toxic to various life stages of S. zeamais at relatively short exposure periods. At the LC₅₀ and LC₉₅ levels, the most susceptible stage was the egg stage followed by larvae, pupae and adults (1-day mortality). The egg was found to be most susceptible to MI, requiring 0.81 and 2.16 mg/l for 50 and 99% mortality, respectively, while the adult was most tolerant, requiring 2.30 and 3.02 mg/l for 50 and 99% mortality, respectively, based on 1-day mortality count. Pupae were less susceptible to MI than egg and larvae, requiring 1.47 and 3.19 mg/l for 50 and 99% mortality, respectively. Based on the present toxicity tests, MI has the potential for use as a fumigant to control all developmental stages of the maize weevil, S. zeamais .     

The effect of temperature on the development and life cycle regulation of the pine weevil Hylobius abietis and the potential impacts of climate change

• 1 The pine weevil Hylobius abietis is widely distributed in the Palaearctic region where it is a major pest. Although predominantly semi‐voltine, with a 2‐year life cycle, the generation time across its range can vary from 1 to 4 years. The duration of the life cycle and the seasonal timing of weevil activity affect the economic impact and management of this pest, all of which are likely to change in a warming climate.
• 2 To determine the effect of temperature and tree species on weevil growth and development, laboratory experiments were performed with eggs, larvae, prepupae, pupae and adults, using, as appropriate, the host species Scots pine Pinus sylvestris L. and Sitka spruce Picea sitchensis (Bong.) Carr. under constant or alternating temperatures.
• 3 The development rate was linearly related to temperature, with developmental thresholds for eggs, larvae and pupae of 8, 4.5 and 7.3 °C, respectively. Day‐degrees were estimated for each life stage. Larval development was affected by tree species, being slower on Sitka spruce than on Scots pine, and was faster under alternating than constant temperatures.
• 4 The development time for prepupae was highly variable, with an apparent facultative prepupal diapause initiated by temperature. The temperature range 20–17.5 °C marked the transition between median prepupal development times of approximately 25 and 90 days. The prepupal stage may serve to minimize the risk of overwintering mortality in the pupal stage and help to synchronize the life cycle.
• 5 Larval and adult mass was positively related to developmental temperature, demonstrating an inverse temperature size rule, and weevils were heavier when developing on Scots pine than Sitka spruce. Development in alternating temperatures reduced weevil mass on Scots pine. The influence of temperature on weevil mass is likely to have a positive effect on fecundity and overwintering survival. The effects of climate change on development, voltinism and weevil mass are discussed.

     

Elimination ofSitotroga cerealella (Olivier) bySitophilus zeamais Motschulsky from mixed laboratory cultures on maize

This paper describes a series of experiments conducted to determine why Sitophilus zeamaisMots . and Sitotroga cerealella (Oliv. ) could not survive together in maize cultures in the laboratory. The effect of S. zeamais on different developmental stages of S. cerealella was investigated. The presence of adult S. zeamais slightly affected moth copulation, egg laying and moth eggs in a mixed culture, but large numbers of developing moths inside maize grains were killed by the adult weevil through feeding on the grains. The major cause of elimination of S. cerealella by S. zeamais from mixed cultures was therefore found to be damage to the immature moths in grain and such moth mortality increased as the developing moths became bigger in the grains. A weevil: grain ratio of approximately 1.4∶1 was found to be the critical weevil density at which the moth disappeared from the mixed cultures.     

Relative importance of natural enemies and abiotic factors as sources of regulation of mealybugs (Hemiptera: Pseudococcidae) in Brazilian coffee plantations

In the present study, we determined the critical stages and the key factors of mortality for Planococcus citri (Hemiptera: Pseudococcidae) in Brazilian coffee plantations using a life table to understand the role of natural biological control on its population. Predators, parasitoids, rainfall, sunlight, physiological disturbances and fungal diseases were collectively responsible for 98.79% in the total mortality of P. citri. Predators belonging to the Chrysopidae, Syrphidae, Dolichopodidae and Coccinellidae families were the most important mortality factors in the early developmental stages of P. citri (i.e. eggs and 1st and 2nd instar nymphs), whereas predators belonging to the Coccinellidae and Chrysopidae families were the most important mortality factors for the last instars (i.e. 3rd instars and adults) for P. citri. The generalist predators Harmonia axyridis, Chrysoperla genanigra and Chrysoperla externa were the key mortality factors for P. citri. The third nymph stage was considered the critical life stage (i.e. the life stage that most influences population size). Our results show that generalist predators and climatic factors are important sources of natural mortality of P. citri governing the population dynamics of this pest in the field.     

Demographic population structure of a leafy epixylic hepatic Anastrophyllum hellerianum (Nees ex Lindenb.) R.M.Schust

Understanding the population processes is central when assessing proper conservation acts, especially in the case of species which inhabit temporal and patchy substrates, such as decaying wood. In epixylic bryophytes, however, only little is known of the demographic population structure and within-population dynamics. In this study on a leafy epixylic hepatic, Anastrophyllum hellerianum (Nees ex Lindenb.) R.M.Schust., a set of demographic traits is investigated, including colony area and size, proportions of the sterile, gemmiparous or sexual developmental stages, the shoot size class distribution among the developmental stages, and numbers of asexual propagules present on the shoots. The estimates of mortality are assessed on the basis of the proportions of dead shoots found in the colonies. The size distribution within the developmental stages of this species shows that a certain threshold size is required for both asexual and sexual reproduction. The shoot size is negatively correlated with density, whereas the numbers of asexual gemmae and the proportions of developmental stages are not affected by shoot density. Furthermore, provisional estimates are calculated for the transitions from early developmental stages to reproductively mature stages. The results indicate that the initial phases of the gametophyte development are the most vulnerable.     

Effect of temperature on the development of the West Indian sweet potato weevil, <Emphasis Type="Italic">Euscepes postfasciatus</Emphasis> (Fairmaire) (Coleoptera: Curculionidae) on an artificial diet

The relationship between temperature and the development of the West Indian sweet potato weevil, Euscepes postfasciatus, on an artificial larval diet containing powdered sweet potato root, was examined at different fixed temperatures from 22 to 31°C. The developmental periods for egg, larvae, and pupae stages shortened in correlation with increased temperature. The thermal constant was 769.2 degree-days and the developmental zero for female and male was 11.1 and 11.7°C, respectively. Although we can rear this weevil at temperatures ranging from 22 to 31°C, rearing temperatures should be kept between 25 and 28°C because the developmental stages were too long at 22°C and the larval period was delayed at 31°C. The basis for these developmental data will be a useful key factor in designing a plan to eradicate the weevil by using a mass-rearing system and SIT.     

Assessing immunocompetence in red palm weevil adult and immature stages in response to bacterial challenge and entomopathogenic nematode infection

Parasites and pathogens can follow different patterns of infection depending on the host developmental stage or sex. In fact, immune function is energetically costly for hosts and trade‐offs exist between immune defenses and life history traits as growth, development and reproduction and organisms should thus optimize immune defense through their life cycle according to their developmental stage. Identifying the most susceptible target and the most virulent pathogen is particularly important in the case of insect pests, in order to develop effective control strategies targeting the most vulnerable individuals with the most effective control agent. Here, we carried out laboratory tests to identify the most susceptible target of infection by infecting different stages of the red palm weevil Rhynchophorus ferrugineus (larvae, pupae, male, and female adults) with both a generic pathogen, antibiotic‐resistant Gram‐negative bacteria Escherichia coli XL1‐Blue, and two specific strains of entomopathogenic nematodes (EPNs), Steinernema carpocapsae ItS‐CAO1 and Heterorhabditis bacteriophora ItH‐LU1. By evaluating bacterial clearance, host mortality and parasite progeny release, we demonstrate that larvae are more resistant than adults to bacterial challenge and they release less EPNs progeny after infection despite a higher mortality compared to adults. Considering the two EPN strains, S. carpocapsae was more virulent than H. bacteriophora both in terms of host mortality and more abundant progeny released by hosts after death. The outcomes attained with unspecific and specific pathogens provide useful information for a more efficient and sustainable management of this invasive pest.     

Mortality of life stages of cowpea weevil (Coleoptera: Bruchidae) exposed to low pressure at different temperatures

Previous studies have shown that low pressure creates a low oxygen controlled atmosphere that can kill stored-product insects. The current study was conducted to determine the mortality of life stages of the cowpea weevil, Callosbruchus maculatus (F.) (Coleoptera: Bruchidae), exposed to different low pressures and temperatures for various exposure periods. The adults were the most susceptible life stage to low pressure; 99% mortality was achieved within 0.8 h at 32.5 mmHg, 30 degrees C. The pupae were the most tolerant life stage to low pressure, requiring exposure periods between 28.98 and 153.20 h at temperatures of 20-35 degrees C to achieve 99% mortality. Mortality increased with exposure time and also with increasing temperature in all life stages. Early stage eggs (3 h old) and late stage eggs (48 h old) experienced higher mortality (values for LT99 of 42.331 and 46.652 h, respectively) compared with intermediate aged eggs (24 h old; LT99 of 74.735 h) under the same conditions of low pressure and temperature. Dried beans, including cowpea, Vigna unguiculata (Walp.), are currently protected with fumigants. Application of low pressure as a pest management tool represents a potential nonchemical alternative to fumigants such as methyl bromide and phosphine for controlling the cowpea weevil and related bruchids.     

Biology ofHyphantria cunea Drury (Lepidoptera: arctiidae) in Japan. V. Preliminary life tables and mortality data in urban areas

Studies on the population dynamics of the fall webworm, Hyphantria cunea have been carried out at three survey stations and along selected roads in the urban area of Tokyo since 1966. Twelve survivorship curves obtained during two years and 8 life tables show that the mortality rate in early developmental stages of the fall webworm is remarkably low as compared with that of other lepidopterous defoliaters and the mortality rate in later developmental stages is compensatory high. The low mortality rate in early stages is considered to be due to the protective role of the nest-web and the lack of egg and larval parasites. All but one parasitic species emerge from prepupae and pupae. Spiders living in the nest-web of the fall webworm play an important role in reducing the number of young larvae. Direct observations and caging experiments showed that relatively high mortality during later larval stages is mainly due to predation by birds (in the first generation) and wasps (in the second generation). The generation mortality in the survey stations always exceeded the level where the population is kept at the steady state, and the outbreak of this moth is considered to be continued by the immigration of adults from large trees growing in gardens on which the larvae can escape from predation pressure.     

Life history of the Onopordum capitulum weevil Larinus latus (Coleoptera: Curculionidae)

The population structure and stage-specific survival of the capitulum weevil, Larinus latus, a potential control agent for weedy Onopordum thistles in Australia, was studied in its native range in Greece. Although fecundity of this univoltine insect was low (35.4 eggs/female), survival was relatively high, with 45% of eggs reaching adulthood when protected from predators and parasitoids, and 23% surviving when exposed to these natural enemies. Other mortality factors of importance for immature stages were a failure to establish, due largely to oviposition by females on inappropriate sites on the thistle capitula, and inter- and intraspecific competition for larval resources. Once emerged, adult losses due to overwintering mortality and net migration were estimated at a further 48%. Despite these losses there was a net doubling of the population at the study site between Onopordum flowering seasons. The data suggest that movement of adults occurs both within and between patches and that variability in population size relative to the resource base is low. Overall, L. latus may be considered a K-strategist which forms relatively stable populations over a fragmented habitat and which maintains its population integrity through a certain degree of annual redistribution. The implications of these data for the potential effectiveness of L. latus as a biological control agent of weedy Onopordum spp. are discussed.     

Elevated water temperature impairs fertilization and embryonic development of whitefish Coregonus lavaretus

The adverse effects of high temperatures on the early life stages of anadromous whitefish Coregonus lavaretus were experimentally examined by assessing fertilization success, the percentage of developmental abnormalities, cumulative mortality and the rate of embryogenesis across a range of temperatures. Temperatures ≥ 7° C increased the proportion of unfertilized and abnormally dividing eggs, deformed embryos and consequent mortality. The higher the temperature, the more severe were the effects. When eggs were fertilized and constantly incubated at various temperatures, the effective level for 50% of the eggs and embryos (EL50) of temperature was 7·6° C at the developmental stage when eye pigmentation was visible. Fewer developmental abnormalities and a lower cumulative mortality rate were observed when embryos were exposed to high temperatures from the later, gastrula stage, than from fertilization or the four‐cell stage. Irrespective of retarded development in terms of day‐degrees (i.e. the sum of daily mean temperatures), a high incubation temperature reduced the development time of C. lavaretus, leading to earlier hatching, and hatched fry were shorter than at the reference temperature of 4–5° C. Global warming will particularly pose risks for stenothermic species such as C. lavaretus, with early life stages being especially susceptible. Thus, relatively small increases and fluctuations in river water temperatures during the spawning season of this anadromous species may have substantial negative impacts on its recruitment and population persistence.     

An alternative method for assessing early mortality in contemporary populations

Biological anthropologists are interested in a population's early mortality rates for a variety of reasons. Early mortality (infant or juvenile) is of obvious importance to those interested in demography, but early mortality statistics are useful for life history analysis, paleodemography, and human adaptability studies, among others. In general, the form of mortality statistics is derived from demography, where chronological age is the gold standard for statistical calculation and comparison. However, there are numerous problems associated with the collection, analysis, and interpretation of early mortality statistics based on age, particularly for anthropological research, which is often conducted in small or non-calendrical-age numerate populations. The infant mortality rate (IMR), for example, is notoriously difficult to determine in populations where accurate accounting of age is not routine, and yet it is widely used in demography, public health, medicine, and social science research. Here we offer an alternative to age-based early mortality statistics that makes use of human biologists' interest in, and skill at, assessing human growth and development. Our proposal is to use developmental stages of juveniles instead of relying exclusively on age as the basis for mortality statistics. Death or survival according to a developmental stage (such as crawling or weaning) may provide more accurate data that are also more closely related to the cause of death. Developmental stages have the added advantage of putting infants and children back at the center of the discussion of early mortality by focusing on their activities in relation to their environment. A case study from the Turkana population of Kenya illustrates the use of developmental stages in describing early mortality. Am J Phys Anthropol 107:315–330, 1998. © 1998 Wiley-Liss, Inc.     

Temperature-dependent development and reproduction of the boll weevil (Coleoptera: Curculionidae)

Abstract Effects of temperature on development, survival, and fecundity of boll weevil, Anthonomus grandis grandis Boheman, were assessed at 10, 11, 12, 15,20,25,30,35,45, and 46 °C; 65% relative humidity; and a photoperiod of 13:11 (L: D) h. The mortality of boll weevil immature stages was 100% at 12°C and decreased to 36.4% as the temperature increased to 25°C. When the temperature increased from 30 °C to 45 °C, the mortality of weevils also increased from 50.1% to 100%. From 15°C to 35°C, the bollweevilpreimaginal development rate was linearly related to temperature. The average development time of total boll weevil immature lifestages decreased 3.6-fold and the preovipositional period decreased 3.3-fold when the temperature was increased from 15°C to 30°C. The lower threshold for development was estimated at 10.9, 6.6, 7.0, and 9.0 °C for eggs, larval, pupal, and total immature stages, respectively, with total thermal time requirement to complete immature stages of 281.8 DD (degree day) (15°C) and 247.8 DD (35 °C). At 1LC and 46°C, weevil females did not oviposit. Longevity of adult females decreased 4.6-fold with increasing temperatures from 15°C to 35°C. Fecundity increased with increasing temperatures up to 30°C and significantly decreased thereafter. These findings will be useful in creating a temperature-based degree-day model for predicting the occurrence of key life stages in the field. An accurate predictor of a pest's development can be very important in determining sampling protocols, timing insecticide applications, or implementing an integrated pest management control strategy targeting susceptible life stages.     

Suppression of Boll Weevil (Coleoptera: Curculionidae) Infestations on South Texas Cotton by Augmentative Releases of the Parasite Catolaccus grandis (Hymenoptera: Pteromalidae)

Augmentative releases of Catolaccus grandis (Burks) were conducted in a series of south Texas cotton fields during 1992 (April 30-June 29) in an attempt to suppress infestations of boll weevil, Anthonomus grandis Boheman. Within each of three release sites, the average incidence of mortality occurring among susceptible host stages (94.4-96.4% and 86.1-96.6% apparent mortality among third-stage larvae and pupae, respectively) was substantially greater than that occurring among these same stages in controls devoid of parasites (2.2-9.6% and 1.8-7.9% apparent mortality, respectively). Such differential mortality produced two important effects: (1) a significant reduction in densities of adult boll weevils produced in release sites relative to controls (0.0-0.1 and 0.3-1.6 unemerged adults/m², respectively), and (2) a concomitant reduction in the incidence of damaged bells during the postbloom period (0.2-0.4% and 48.3-91.7% in release and control sites, respectively). These results conclusively demonstrated the ability of C. grandis to suppress and maintain boll weevil infestations at subeconomic levels when augmented in sufficient quantities during the period in which the first and second host generations normally develop on cultivated cotton. The potential for augmentative biological control of boll weevil in the south Texas cotton environment is discussed.     

Population field studies of the aphidophagous ladybird beetleHarmonia axyridis (Coleoptera: Coccinellidae): Life tables and key factor analysis

1. Life tables of the predatory ladybird beetle Harmonia axyridis were analysed by taking samples from twenty or twenty four sites colonized by eight species of aphids for two years.
2. Larval mortality was a key factor in the H. axyridis populations. Mortality of all the stages tended to be density-dependent when life cycles were divided into four developmental stages, except in the case of mortality at hatching due to sibling cannibalism.
3. Sibling and non-sibling cannibalism played an important role on population stability and persistence.

     

Modeling the interaction between the exotic invasive aquatic macrophyte <Emphasis Type="Italic">Myriophyllum spicatum</Emphasis> and the native biocontrol agent <Emphasis Type="Italic">Euhrychiopsis lecontei</Emphasis> to improve augmented management programs

Mathematical modeling is used to investigate control of the invasive aquatic plant Myriophyllum spicatum L. by the native watermilfoil weevil Euhrychiopsis lecontei Dietz. An age-structured population model with discrete development class is used to separate the destructive activity of Euhrychiopsis lecontei Dietz larvae from the relatively benign activity of the other developmental stages. Empirical model behavior is evaluated and agrees with expected system characteristics. Simulation results demonstrate diminishing returns in the control impact of E. lecontei Dietz as a function of population stocking density. These results indicate that predictive modeling of this type may be used to optimize the utilization of Euhrychiopsis lecontei Dietz as a biological control agent.     

Mortality factors affecting Bemisia tabaci populations on cotton in Turkey

Cohort‐based, partial life tables were constructed to determine the sources and rates of mortality factors affecting Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on cotton in the eastern Mediterranean region of Turkey over a two year period. Mortality factors were recorded as due to predation, parasitism, dislodgement and unknown for five developmental stages. Across 10 independent cohorts, the highest median rate of marginal mortality pooled over all stages was attributed to parasitism (0.69) followed by predation (0.67). The key factor was hypothesized to be parasitism based on graphical and regression‐based comparison of individual factor k‐values to total generational mortality. The greatest amount of marginal immature mortality occurred during the fourth nymphal stadium (median = 0.77) and mortality during this stage was also most predictive of variation in total mortality. Pooled over all developmental stages, the highest rates of irreplaceable mortality were associated with parasitism (median: 0.112), followed by predation (0.088), dislodgement (0.020) and unknown (0.017). Although crawler mortality was not explicitly measured, sensitivity analyses indicated that mortality during this stage would have changed total mortality by only 0.45–1.21% and had no effect on identification of key factors. There was no significant effect of cotton cultivar on any mortality factor or total mortality over the two years of study. Results suggest that conservation of natural enemies, particularly parasitoids, may provide for more sustainable management of B. tabaci on cotton in Turkey.     

Mortality factors affecting the cabbage seedpod weevil,Ceutorhynchus obstrictus (Marsham), in its area of origin: A life table analysis

The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is a widely distributed invasive pest of cruciferous crops in North America. Control measures rely mostly on the application of insecticides but alternative control strategies such as classical biological control are under evaluation. To investigate the impact of parasitoids and other mortality factors on C. obstrictus populations, life table studies were conducted between 2005 and 2007 in 13 winter oilseed rape fields in Switzerland, part of the native range. Under field conditions females only realized approximately 50% of their potential lifetime fecundity, varying between 96 and 631 eggs per individual. Total generational mortality was higher than 99.6% in each year. Overwintering mortality of adults was the major population limiting factor, contributing approximately 50% to the overall generational mortality of C. obstrictus, whereas factors acting on the immature stages were responsible for the remaining 50%. Among the mortality factors of the immature stages, egg, larval and pupal mortality contributed 9–12%, 25–28% and 4–6% to the generational mortality, respectively. Larval ecto-parasitism on its own accounted for 7–15% of the generational mortality. Comparison of life table data presented here with that from North America will be invaluable for elucidating the mortality factors that regulate C. obstrictus populations in Europe, the region of origin.