Effects of gamma radiation on spermatophore production and reception and subsequent fecundity and egg viability inAcarus siro L. (Acari: Acaridae)

Gamma radiation at doses higher than 10 krad significantly lowered the fecundity of the grain mite,Acarus siro. The fecundity of irradiated females was inversely correlated with dose, both when control or irradiated males were used in the pairing.Irradiation with ionizing radiation affected sexual activity of males. At doses above 10 krad the number of formed or observed spermatophores was lowered significantly.Sexual attractiveness of irradiated and control females to irradiated males was similar. However, non-irradiated males were observed mating more often with non-irradiated than with irradiated females.No correlation was found between the numbers of spermatophores present in the spermathecae of the female and the fecundity of the female. Irradiation had a greater effect on fecundity of the female than on sexual activity of the male; it did not affect the shape or behavior of spermatophores in the spermathecae of the female.Viability of eggs laid by females decreased by at least 50% when females or males were irradiated with doses above 20 krad. Irradiation also affected the survival of adults, but females were more sensitive than males. Net sterility index indicates that doses higher than 20 krad induce more than 90% sterility.     

Thermal acclimation in the grain miteAcarus siro (Acari: Acaridae)

Grain mites reared on wheat germ at 21±1°C and 85% r.h. were treated (acclimated) as adults at 0, 14, 28 or 33°C for 1 or 4 days. Fecundity, longevity and numbers of F₁ females and males produced were compared. A treatment of 1 day was enough to acclimateAcarus siro and change the studied developmental parameters. Acclimation always lowered fecundity but the magnitude of the effect was dependent upon the temperature regime. The number of males and females emerging differed greatly among various temperature regimes; however, the sex ratio of emerged adults remained in most instances quite constant.     

Effects of alternating temperatures onAcarus siro L. (Acari: Acaridae)

Fecundity, longevity and survival to adulthood ofAcarus siro (L.) at constant and alternating temperatures were compared. Both fecundity and longevity were affected by alternating temperatures but the effect of the frequency of alternations was not significant. Significantly higher fecundity and longer life spans were recorded at constant temperatures of 14 and 21°C than at 28°C or at alternating temperature regimes. Alternating temperature regimes in comparison to constant regimes did not significantly change the number of males and females surviving to adulthood or the sex ratio. However, the lowest number of adults surviving was recorded when temperatures were changed every 12 h and the highest at a constant temperature of 14°C.     

Laboratory Studies on the use of Two New Arenas to Evaluate the Impact of the Predatory Mites Blattisocius tarsalis and Cheyletus eruditus on Residual Populations of the Stored Product Mite Acarus siro

Residual populations of storage mites sheltering in crevices and cracks escape conventional control treatments and are implicated in the infestation of newly harvested grain. In a series of 24 h laboratory tests, the performance of solitary adults of two predatory mite species, Cheyletus eruditus (Schrank) and Blattisocius tarsalis (Berlese), were assessed for controlling small numbers of the flour mite Acarus siro (L.). Tests were carried out in the presence or absence of prey refuges or grain debris to afford shelter to the flour mites. While C. eruditus had a significant effect on the motile stages of A. siro, in contrast B. tarsalis had a significant effect on the eggs. The maximum percentage of motile stages of A. siro eaten by C. eruditus was 82%, whereas the minimum percentage of A. siro eggs eaten by B. tarsalis was 99%. While the performance of C. eruditus in predating on motile stages of the flour mite was hindered by the presence of the prey refuge (38% eaten) and grain debris (25% eaten), the performance of B. tarsalis in predating on flour mite eggs was unaffected (100% eaten in presence of prey refuge or grain debris). In prolonged exposures (36 days) the performance of 2, 4 or 8 adult predators, either a single species or a combination of both, was assessed for their ability to control a population of the flour mite developing up to F₂ from an initial inoculum of 80 females and 20 males, allowed to oviposit for 72 h in the absence of predatory mites. The maximum reduction in prey population of 80% was achieved with eight B. tarsalis. Combining the two predatory species did not enhance the reduction of A. siro population.     

The effect of crowding on adult populations ofDelia (=Hylemya) antiqua (Meigen)

Using 5 density levels, the effect of increasing density was studied on several population statistics of adult Delia (=Hylemya) antiqua. Amongst the statistics studied were adult lifespan; female mating frequency, fecundity and egg hatchability. It was shown that females lived significantly longer than males and that increasing density significantly reduced lifespan. Density had no effect on mating frequency. Total fecundity/female was significantly reduced with increasing density but oviposition rate was density independent. Using these statistics, mean generation time T, net reproduction rate R₀ and capacity for increase r_c were calculated at the different density levels. Values of R₀ showed a one-tailed response but there was no clear effect of density on r_c. Multiple comparisons between variables revealed several important relationships.

1. Adult lifespan was the most important factor affecting egg production.
2. Number of mated females was more important in affecting total fecundity/cage than adult density.

It could also be calculated that to produce the effect of one single mated female on total fecundity/cage the overall density would have to be reduced by 0.0023 individuals/cm³. These results are discussed in the context of efficient laboratory rearing of the onion fly.     

Population specific fitness response of Drosophila subobscura to lead pollution

Abstract Differences in heavy metal tolerance among separate populations of the same species have often been interpreted as local adaptation. Persistence of differences after removing the stressor indicates that mechanisms responsible for the increased tolerance were genetically determined. Drosophila subobscura Collin (Diptera: Drosophilidae) populations were sampled from two localities with different history of heavy metal pollution, and reared for eight generations in the laboratory on a standard medium and on media with different concentrations of lead (Pb). To determine whether flies from different natural populations exposed to the Pb‐contaminated media in the laboratory show population specific variability in fitness components over generations, experimental groups with different concentrations of lead were assayed in three generations (F₂, F₅, and F₈) for fecundity, developmental time, and egg‐to‐adult viability. On the contaminated medium, fecundity was reduced in later generations and viability was increased, irrespective of the environmental origin of populations. For both populations, developmental time showed a tendency of slowing down on media with lead. Faster development was observed in later generations. Preadaptation to contamination, meaning higher fecundity, higher viability, and faster egg to adult development in all studied generations, was found in D. subobscura originating from the locality with a higher level of heavy metal pollution.     

Consequences of diapause on post‐diapause development,reproductive physiology and population growth of Chilo partellus (Swinhoe)

We investigate the effects of diapause on post‐diapause development, reproductive physiology and population growth of Chilo partellus (Swinhoe) (Crambidae: Lepidoptera). Aestivating and hibernating larvae of C. partellus are exposed to diapause terminating conditions (consisting of an LD 12 : 12 h photocycle at 27 ± 1 °C and 65 ± 5% relative humidity with a fresh diet) to terminate the diapause and observations are made on percentage pupation, pupal duration and weight, adult reproductive performance and population growth parameters. We find that the diapause in C. partellus significantly reduces the percentage pupation and weights of pupae, ultimately lowering the weight and reproductive performance of adults. Reduced weights of adult females are found to be directly associated with a lower number of egg cells in ovaries. Nevertheless, the reproductive performance of C. partellus males is also found to be greatly affected in the diapause (hibernation and aestivation) experiencing population in terms of the deposition of a lower number of spermatophores and eupyrene sperm in the reproductive tracts of females compared with the nondiapausing population. The results of the present study clearly indicate that a reduction in longevity, fecundity and egg viability, as well as a reduced rate of deposition of spermatophores and eupyrene sperm, in a diapause experiencing population of C. partellus ultimately leads to a reduction in population growth parameters, thus having implications for bio‐ecology and population dynamics under a changing climatic scenario.     

Pirimiphos-methyl resistance in two stored product mites, Acarus siro and Acarus farris, as detected by impregnated paper bioassay and esterase activity assays

The response to pirimiphos-methyl, in one strain of Acarus farris and two strains of Acarus siro, was assessed using an impregnated filter paper bioassay and by the selection of adults following exposure to pirimiphos-methyl. It was concluded that one of the strains of A. siro was resistant to pirimiphos-methyl and that a major resistance mechanism was involved. The second strain of A. siro gave a response similar to that of a laboratory strain unexposed to organophosphates and was considered to be susceptible. The A. farris strain responded to selection at the ED50 but not at the ED99, and it was concluded that a minor resistance mechanism is present in this strain. Assays of esterase activity were used to attempt to identify the biochemical mechanisms involved in the resistance detected by the bioassays. The A. farris and susceptible A. siro strains showed similar levels of esterase activity but the esterase activity of the resistant A. siro strain was significantly greater. An increase in esterase activity followed selection of both the A. farris strain and the resistant A. siro strain. An acetylcholinesterase assay showed no significant difference between the susceptible and pirimiphos-methyl selected strains of A. siro. The results suggest that esterases are involved in the resistance to pirimiphos-methyl found in A. siro and A. farris but that in A. siro, at least, other mechanisms may also be present.     

Isolation and characterization of microsatellite loci in the flour mite Acarus siro

Thirteen microsatellites with dinucleotide repeats were isolated from genomic DNA in solution by hybridization capture. Eleven were evaluated against Acarus siro using a multiple‐tube approach to assess polymorphism and reliability of the results. The multiple‐tube method demonstrated the presence of null alleles due to low levels of DNA. Seven of the 11 microsatellite loci were polymorphic and six produced reliable amplification products, if results only from individuals that scored at all six loci were used in the analysis. These were evaluated in eight strains of A. siro. Two of the samples showed some genetic divergence using F_ST values.     

Stimulation of egg production in the grain miteAcarus siro by the juvenile-hormone analogue fenoxycarb

The insect juvenile-hormone analogue fenoxycarb (ethyl [2-(phenoxyphenoxy) ethyl] carbamate) has been shown to stimulate egg production in the flour miteAcarus siro L. Incorporation of fenoxycarb into mite food at 10 mg kg^–1 and 100 mg kg^–1 increased egg production by 43% and 99%, respectively. In addition, total mite populations were significantly higher in fenoxycarb-treated media than in controls. These results are discussed in relation to the possible gonadotropic role of juvenilehormone-like molecules in mites, and to the use of fenoxycarb as a grain protectant.     

Toxicity of six novel fungicides and sulphur to <Emphasis Type="Italic">Galendromus occidentalis</Emphasis> (Acari: Phytoseiidae)

A laboratory evaluation of fenbuconazole, myclobutanil propiconazole, boscalid, fenhexamid and pyraclostrobin revealed these fungicides to be harmless to adult Galendromus occidentalis. None of these fungicides affected adversely fecundity and egg viability. Elemental sulphur also had no effect on adults and fecundity. However, 72.4% of the young larvae perished after hatching. The six novel fungicides are safer alternatives to sulphur in perennial crops in British Columbia.     

Energy budget of the grain mite,Acarus siro (Acari: Acaridae)

Immature individuals ofAcarus siro L. ingest a total of 0.1408 J of food energy, 58.5% of which is consumed by the deutonymph, 27.1% by the protonymph and only 14.1% by the larva. The total ingestion is much greater (2.8169 J±0.0981se). Much energy, 0.7031 J±0.0231se, is used for egg production, which is concentrated in the first 20 days of adult life. Assimilation efficiency during this period varies from 63 to 71%. Most energy ingested between the 20th and 40th days of adult life is used in biomass production, and biomass increases significantly up to th 30th day. Afterwards, old individuals expend a large amount of assimilated energy on respiration due to the increased cost of maintenance.Present address: Biology Dept., LB 8042, Georgia Southern University, Statesboro, GA 30460, U.S.A.     

Effects of pyriproxyfen on ovarian development and fecundity ofRhagoletis pomonella flies

Three-day old female apple maggot flies,Rhagoletis pomonella (Walsh), were topically exposed to different doses (0.1, 1, 10, and 100 μg per fly) of a juvenile hormone mimic, pyriproxyfen, in the laboratory. Pyriproxyfen had little lethal effect on females except at the extremely high dose of 100 μg. It also had no significant effect on egg viability of treated females. A non-lethal dose of 1 μg per fly did, however, enhance significantly the fecundity (egg production) as well as the ovarian development (number of eggs in ovaries and length of egg folicles) of treated flies. We conclude that pyriproxyfen could be a useful aid in exploring endocrine regulation of feeding and reproductive physiology behavior inR. pomonella, about which current knowledge is scant.     

Selection for developmental time in bean weevil (Acanthoscelides obtectus): correlated responses for other life history traits and genetic architecture of line differentiation

In this article we investigate the direct and correlated responses to selection for developmental time in order to discern differences between lines in several preadult and adult life history traits of Acanthoscelides obtectus (Coleoptera, Bruchidae). Selection for fast development was about five times as effective as selection for slow development, as judged by realized heritabilities. The correlated responses on the following life‐history traits were studied: egg size, hatching success, embryonic developmental time, egg‐to‐adult viability, body weight, first day of egg laying, total fecundity, and longevity. Analyses of the terminal generation of selection showed that all life history traits examined, except for hatching success, were affected by selection. The findings suggest that body weight, total fecundity, and longevity traded off to preadult developmental time. Unlike the adult traits, none of the preadult traits showed negative correlations with developmental time. We also present data concerning the underlying genetic basis that produces changes in preadult developmental time, body weight, and egg‐to‐adult viability in the lines selected for fast and slow preadult developmental time. Additive‐dominance genetic architecture for both preadult developmental time and body weight was found. In addition, it appears that the responses to selection for preadult developmental time involved between 10 and 28 loci, which were correlated with at least one to four genes for body weight. Epistasis makes a significant contribution to genetic divergence between fast and slow selected lines only with respect to preadult viability. The observed levels of dominance and epistasis underscore the important role of nonadditive genetic effects to the adaptive diversifications of bean weevil populations.     

Effects of delayed mating and male mating history on the reproductive potential of Leucoptera coffeella (Lepidoptera: Lyonetiidae)

Abstract 1 Despite the importance of Leucoptera coffeella (Guérin‐Mèneville) in coffee production worldwide, there is a lack of information on its reproduction. This knowledge will help in mass rearing, and support the development of behavioural control techniques for this insect. The present study determined the effects of delayed mating and previous matings of male L. coffeella on fecundity, egg viability and frequency of female remating. 2 The highest levels of fecundity and egg viability were obtained from matings of 1–3‐day‐old females. When females mated at 5 days of age, there were reductions of 40% in oviposition and of 43% in egg viability. 3 Females mated with 2‐day‐old virgin males were more fecund than those mated with older males; egg viability was also low (18%) from females mated with older males. 4 Virgin females that mated with virgin males laid a greater number of eggs than those mated with previously copulated males. Egg viability decreased with the increase in the number of previous male matings. 5 Five‐day‐old females remated in greater proportion than 2–3‐day‐old females. Females that copulated with males that had previously mated three times had higher rates of remating than those that copulated with virgin males. 6 The results obtained indicate that 1–3 days after emergence is the optimum age for mating. The implications of these findings for the control of L. coffeella by synthetic sex pheromone are discussed.     

A laboratory evaluation of a regulated airflow through wheat at four combinations of temperature and humidity on the productivity of three species of stored product mites

Aeration is a promising alternative to the use of pesticides for the control of storage insects by cooling bulk grain, but its effectiveness against mite pests is neither fully understood nor optimised. For this reason, the productivity of three species of storage mites, Acarus siro, Lepidoglyphus destructor and Tyrophagus longior, was studied in a laboratory-based experiment at four combinations of temperature and humidity (10°C and 70% RH, 10°C and 80% RH, 20°C and 70% RH, 20°C and 80% RH) with and without an airflow (at 10 m³/h/tonne, equalling 2.5 l/s/tonne, in tubes containing 15 g of grain). This is the first time that a study has examined the three principal components of aeration separately from each other. The effect of these factors was different for each species. For A. siro, temperature was the most important factor, while airflow and humidity were of similar but lesser importance. For T. longior, temperature was more important than humidity, while the reverse was true for L. destructor. For these two species, airflow was the least important factor. The airflow decreased the productivity of L. destructor and T. longior but increased the productivity of A. siro. This increase in productivity confirms that, in practice, prevention of mite infestations, in particular A. siro, will require storage of grain at low temperature, relative humidity and moisture content. This revised version was published online in July 2006 with corrections to the Cover Date.     

Combination of the antifeedant bean flour and the predator Cheyletus malaccensis suppresses storage mites under laboratory conditions

Stored product mites are pests of serious economic and medical importance. Recently, it has been shown that the biological control of these pests based on the use of natural compounds and predators had a high potential for success. In this study, we investigated the suppression of three pest mites by combination of the predator Cheyletus malaccensis Oudemans, 1913 and bean flour (Phaseolus vulgaris), which is an antifeedant. Wheat grain (100 g) was contaminated with 100 individuals (Acarus siro (Linnaeus, 1758), Aleuroglyphus ovatus (Troupeau, 1878) or Tyrophagus putrescentiae (Schrank, 1781)). We added bean flour in concentrations of 0, 1, 5 and 10 g kg⁻¹ (wt/wt) and/or the predator with initial predator/prey ratios 0, 1/50, 1/25 and 1/10. The experiment was carried out under abiotic conditions that are optimal for pest development. After 21 days, pest and predators numbers were recorded. Application of flour significantly reduced populations of A. siro, slightly reduced populations of T. putrescentiae, the efficiency increased with increasing concentration. A. ovatus was not affect by bean flour. Populations of all mite species were successfully reduced by the sole addition of C. malaccensis, with a higher efficiency at higher Cheyletus ratios. The additive effect of the predator and flour was mainly apparent in the reduction of T. putrescientae. The population of C. malaccensis was not affected by the presence of bean flour. It is therefore recommended to use bean flour for the reduction of A. siro, a combination of bean flour and Cheyletus for the reduction of T. putrescientae, and only Cheyletus for the reduction of A. ovatus. Handling Editor: Arne Janssen.     

A microsporidian pathogen of the poroporo stem borer,Sceliodes cordalis (Dbld) (Lepidoptera: Pyralidae): Effects on adult reproductive success

Larvae of Sceliodes cordalis were infected over a range of ages and doses with Nosema sp. (NSC). The resulting spore loads in adults ranged from 9.3 × 10⁵ to 8.9 × 10⁷ spores and varied with the age of the larva at infection and with the dose ingested. Infection caused small reductions in female weight, mating success, potential fecundity, longevity, and egg viability. The magnitude of spore loads in female moths was not found to influence any of these factors apart from potential fecundity in very low weight moths. The cumulative effects of infection reduced natality in the laboratory colony from 11,400 to 6000 hatching eggs per 100 females. Laboratory reared, infected females were smaller, had a lower longevity, a reduced spore load, and were more fecund (eggs per milligram adult weight) than infected females from a field population. Manipulation of NSC in a biological control program is not considered to be of any value.     

Host strain specific sex pheromone variation in Spodoptera frugiperda

Background

In the Lepidoptera it was historically believed that adult butterflies rely primarily on larval-derived nutrients for reproduction and somatic maintenance. However, recent studies highlight the complex interactions between storage reserves and adult income, and that the latter may contribute significantly to reproduction. Effects of adult diet were commonly assessed by determining the number and/or size of the eggs produced, whilst its consequences for egg composition and offspring viability were largely neglected (as is generally true for insects). We here specifically focus on these latter issues by using the fruit-feeding tropical butterfly Bicyclus anynana, which is highly dependent on adult-derived carbohydrates for reproduction.

Results

Adult diet of female B. anynana had pronounced effects on fecundity, egg composition and egg hatching success, with butterflies feeding on the complex nutrition of banana fruit performing best. Adding vitamins and minerals to a sucrose-based diet increased fecundity, but not offspring viability. All other groups (plain sucrose solution, sucrose solution enriched with lipids or yeast) had a substantially lower fecundity and egg hatching success compared to the banana group. Differences were particularly pronounced later in life, presumably indicating the depletion of essential nutrients in sucrose-fed females. Effects of adult diet on egg composition were not straightforward, indicating complex interactions among specific compounds. There was some evidence that total egg energy and water content were related to hatching success, while egg protein, lipid, glycogen and free carbohydrate content did not seem to limit successful development.

Conclusion

The patterns shown here exemplify the complexity of reproductive resource allocation in B. anynana, and the need to consider egg composition and offspring viability when trying to estimate the effects of adult nutrition on fitness in this butterfly and other insects.     

Longevity and fecundity ofAcarus siro on four field and eight storage fungi

Egg production and longevity of isolated pairs ofAcarus siro L., when fed on mycelial pellets of selected fungi from shake cultures, were compared with those on a control diet of wheatgerm and brewer's yeast. The mites were always less productive on the fungal diet. They did best on the yeastHansenula anomola and worst on the field fungusAlternaria alternata. There was very little difference between egg production on wheatgerm alone and that on the control diet of wheatgerm and yeast. On the control diet, males lived longer than females. Fungal diets usually shortened male lives, while in two-thirds of the cases female lifespans were unaffected.