Effects of U.V. light and temperature on the melanization and the formation of daily growth layers of Sarcophaga falculata.

Adult Sarcophaga flies, immediately after eclosion, were subjected to different temperature régimes or irradiated with u.v. light. The effect of the treatment on cuticular melanization was studied by comparison with specimens of control series or by comparing the areas of cuticle on the thoracic phragma of the same specimen that were deposited at different times under different conditions. The cuticle of flies that were tanned at 15 or 31°C was less melanized than that of control flies at 26°C. Irradiation with long wave u.v. light suppressed mainly the melanization whereas both the melanization and sclerotization processes were inhibited by short wave u.v. A decrease in adult melanization was caused also by exposure to u.v. of the heads of pharate adults 24 hr before eclosion.     

Biological and biochemical differences between in vitro- and in vivo-reared Exorista larvarum

Quantitative and qualitative parameters of Exorista larvarum (L.) (Diptera: Tachinidae) reared on two insect-material-free artificial media and in the factitious host Galleria mellonella L. (Lepidoptera: Pyralidae) were compared. Significantly higher puparial yields and weights were obtained in both a milk-based and a veal homogenate-based medium than in the factitious host. Longevity and parasitization rates were not different between the in vitro- and in vivo-reared flies. Despite the greater puparial weight of the veal medium-reared E. larvarum females, the number of eggs laid by these females on host larvae was not higher than that of females reared under the other two rearing conditions. Moreover, in a complementary experiment, with homogeneous puparial weights of milk medium- and host-reared females, the former oviposited fewer eggs. Hence, puparial weight alone is not a reliable quality parameter for E. larvarum reared on artificial media. Lower amino acid content, with a deficiency in aromatic amino acids and an excess in proline, was found for in vitro third instar parasitoid larvae reared on both media compared to the in vivo-reared ones. These results suggest a correlation between the amino acid deficiency and imbalance of medium-reared larvae and the lower number of eggs laid by the females obtained.     

Estimation of rates of predation on tsetse

The levels of natural predation of puparial and adult tsetse flies, Glossina pallidipes Austen, were investigated at Nguruman, Kenya, during January 1989. Puparial experiments involved the production, by individually tubed female flies, of naturally deposited, unhandled puparia in soil cores; handled puparia were obtained from groups of caged flies kept in the normal way. Equal numbers of handled and unhandled puparia were planted out at different densities (1, 2, 4 or 8 per linear metre) in fifty-one natural puparial sites in four major vegetation types. After 10 days puparia were recovered using a soil corer and sieving system. Average predation rates (adjusted for the displacement of puparia by vertebrate activity at the puparial sites) were 9.4% and 7.8% for the two types of puparia during the experiment, equivalent to an average loss of 23.7% of all puparia during a normal 30-day developmental period. Maximum potential predation rates of adult flies were investigated by pinning freshly killed adults at densities of 1, 2, 4 or 8 per m3 to natural vegetation and scoring the results after 24 h. 70% of flies were attacked during this time, by a variety of predators, thought to include both vertebrates and invertebrates. No density dependence was detected in the experiments, either because natural puparial densities were too low for it to occur at this stage of the life cycle or because adult predation levels were too high for it to be detected. Present results are compared and contrasted with previous results for this and another species of tsetse. Calculations of the life-time fertilities of female tsetse suggest that the levels of puparial predation revealed by the present experiments are entirely realistic. Behaviour of the adult flies allows them to escape most of the considerable predation pressure under which they live. How they do so remains a mystery.     

Seasonal life cycle and autogeny in the mosquitoAedes togoi in northern Kyushu,Japan, with experimental analysis of the effects of temperature,photoperiod and food on life-history traits

We studied seasonal changes in the larval population structure, adult size, and autogeny (egg production without a bloodmeal) of the mosquitoAedes togoi on the seacoast of northern Kyushu, Japan. The effects of temperature, photoperiod and food conditions on larval development, adult size and autogeny were studied in the laboratory.Aedes togoi overwintered in both the egg and larval stages and was multivoltine. Adult size was greater in spring and autumn and smaller in summer. Autogeny occurred in spring and autumn but not in summer. Autogenous females were larger than anautogenous females, and larger autogenous females produced more eggs. Laboratory experiments showed that autogeny was promoted under low temperature and short-day conditions which corresponded with spring/autumn conditions in the field. Experimental food limitation in the larval stage greatly reduced adult size and autogenous egg production. In the field, large inter-pool variations in adult size and autogeny rate probably resulted from variations in nutrient and crowding conditions. Seasonal autogeny ofAedes togoi was discussed in terms of life-history strategy under fluctuating environmental conditions where relative advantages of autogenous and anautogenous reproduction alternate seasonally.     

Effect of temperature on the larval stage of Tetanocera elata (Diptera: Sciomyzidae) – Potential biological control agent of pestiferous slugs

Due to the considerable losses caused by slugs in terms of agricultural production and revenue, there is an urgent need for a cost effective biological control agent. The malacophagous nature of the sciomyzid fly, Tetanocera elata (Fab.) makes it a possible contender to meet this demand. This study examined the effect of constant temperatures (14, 17, 20, 23, and 26 °C), in addition to ambient outdoor and laboratory temperatures on T. elata larval duration and predation. In general, the mean and median larval stage duration decreased as temperature increased with percentage survival for the overall larval stage (62%) greatest at 20 °C with a median duration of 44 days. There was no significant difference between temperatures with regard to the number of slugs killed per larva and while predation rate increased with increasing constant temperature, there was also no significant difference between the constant temperatures. Our results show that puparial weight can be used to predict the sex of adult flies prior to their emergence. The results are discussed in the context of the suitability of T. elata as a biological control agent of pestiferous slugs.     

Competitive Interactions between Immature Stages of Bactrocera cucurbitae (Coquillett) and Bactrocera tau (Walker) (Diptera: Tephritidae) under Laboratory Conditions

The melon fly, Bactrocera cucurbitae (Coquillett), and the pumpkin fly, Bactrocera tau (Walker), are economically important pests that attack mainly cucurbitacean fruits. The two fruit fly species have similar natural distributions, host ranges, and population growth capacities. This study was designed to assess the asymmetrical competitions through resource exploitation between the larvae of B. cucurbitae and B. tau at different density levels and temperatures, and on different hosts by comparing the relative effects of interspecific and intraspecific interactions on four life history parameters: survival rate, puparial mass, puparial duration, and developmental duration. Our results showed that intraspecific and interspecific competitions occurred under some laboratory conditions, and B. cucurbitae took advantage over B. tau at the high-density level and at low and high temperatures on pumpkin, bitter gourd, and bottle gourd when interspecific competition took place. Intraspecific and interspecific competitions mainly affected the puparial mass and the survival rate of the two fruit fly species but had no marked effect on the puparial duration or development duration.     

Performance of the tsetse, Glossina morsitans morsitans reared under various feeding regimens in Zambia

Groups of Glossina morsitans morsitans Westwood fed at emergence and thereafter daily, every second or third day respectively, up to the end of their first pregnancy cycle, survived well (73–79%) and produced virtually the same number of puparia/ (0.83–0.85) in the same puparial weight class (23–24 mg). However, adult survival (29%), number of puparia/ (0.30) and puparial weight (19 mg) were much lower in the group consistently fed every 4th day after the initial meal at emergence. It is proposed that tsetse colonies could be fed on Mondays, Wednesdays and Fridays without jeopardising adult survival, puparial production/ and the size (weight) of puparia produced.

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Performances en Zambie de la mouche Tsé-Tsé (Glossina morsitans morsitans) élevée en utilisant différents régimes alimentaires

Résumé Afin d'estimer si une alimentation quotidienne de G. morsitans morsitans présente un avantage sur une alimentation moins fréquente, nous avons enrigestré la survie des adultes, la production et le poids des pupes chez des individus nourris à l'émergence et, ensuite, tous les jours ou tous les 2, 3 ou 4 jours. Les femelles alimentées quotidiennement, ou tous les 2 ou 3 jours, ont produit le même nombre de pupes (0,83–0,85), avec des poids de même ordre (23–24 mg), et avec une aussi bonne survie (73 à 79%). Alimentées tous les 4 jours, elles ont produit 0,30 pupe/femelle, pesant 19 mg/pupe et avec une plus faible survie (29%). Ces résultats montrent qu'il est inutile de nourrir les mouches chaque jour au lieu de tous les 2 ou 3 jours. Cependant une alimentation à des intervalles supérieurs à 3 jours, a eu des conséquences clairement défavorables. Ainsi, peuvent être considérablement réduits et le travail et le coût des élevages, sans porter préjudice à la production, en alimentant les mouches 3 fois par semaine, par ex. les lundis, mercredis et vendredis.

     

Effects of temperature and other environmental factors on the post‐diapause development of walnut husk fly Rhagoletis completa (Diptera: Tephritidae)

To more effectively manage walnut husk fly Rhagoletis completa (Diptera: Tephritidae), in California walnut orchards, it is important to understand the factors that affect the timing of adult emergence. In the present study, we examine the effects of incubation temperature, pre‐chill and chill durations, latitude, cultivar and size on the post‐diapause development of R. completa puparia. The lower developmental threshold, upper developmental threshold and optimal temperature for puparial development are estimated to be 4, 34 and 26.6 °C, respectively. The thermal requirement for adult emergence after 120 days of chilling is estimated to be 2024 degree days. Percentage adult emergence declines at both higher and lower incubation temperatures. Chill duration at 5 °C for diapausing puparia has a nonlinear negative effect on the thermal requirement but no effect on percentage emergence. Insufficient chilling leads to poor synchronization of adult emergence. Greater pre‐chill duration at room temperature increases the thermal requirement and slightly decreased percentage emergence. Latitude has a negative effect on the thermal requirement. Puparia from northern California black walnut (Juglans hindsii) have a slightly greater thermal requirement than puparia from cultivated walnut (Julgans regia). There is no significant difference in puparial fresh weight or mean thermal requirement between males and females, although the positive correlation between thermal requirement and puparial fresh weight is stronger for females than males. The effects of temperature and other environmental factors on the post‐diapause development of R. completa are discussed in relation to observations from other Rhagoletis species.     

Reproductive and developmental consequences of a diapause maternal effect in the flesh fly, Sarcophaga bullata

Abstract Progeny of Sarcophaga bullata produced from mothers with a history of short day will not enter pupal diapause even if they are reared in a strong diapause-inducing environment (LD 12:12 h at 20^oC). Short-day exposure and diapause commitment are normally inseparable, but this maternal effect provides a tool for examining separately the effect of photoperiod and diapause commitment. Duration of the wandering period of the third instar is longer in diapause-destined larvae than in non-diapause-destined larvae, and fecundity of flies that have experienced pupal diapause is lower than in long-day flies that have not been through diapause. The puparia of diapausing pupae contain more hydrocarbons than puparia of nondiapausing pupae, and this contributes to higher rates of net transpiration for the nondiapausing flies. Flies showing the maternal effect (short-day experience but no diapause) show an intermediate response: length of wandering, fecundity rate and quantities of puparial hydrocarbon are between the extremes observed in the other two groups of flies. Thus, the maternal effect switches the developmental programme to nondiapause, but the progeny retain some characteristics of diapause. Evidence from reciprocal crosses indicates that the photoperiodic history of the female, rather than the male, is responsible for the influence on fecundity.     

The direction of incident light and its perception in the control of pupal melanization in Pieris brassicae

The rôle of the direction of incident light in pupal melanization of the cabbage white butterfly, Pieris brassicae, was examined by exposing larvae during their sensitive period to various combinations of a light and dark background and of melanization inhibiting and promoting light. The results show that melanization is strongly controlled by the direction of the incident light.By blinding different eyes with black varnish, their rôle in the perception of the brightness contrast was studied. Nearly the same degrees of melanization are achieved as by corresponding arrangements of brightness contrast in the environment. Blinding the most ventrally located ocellus (No. 1) results in maximal melanization; blinding additional ocelli has no additional effect. On the other hand, no influence is observed if only the most dorsal ocellus (No. 6) is blinded.By coating the eyes with colours, their rôle in perception of melanization inhibiting and promoting light was investigated. Melanization is markedly influenced by light perceived via the ventral situated ocelli. In this case, the effect also depends on the number of ocelli involved. All effects may be explained by a mechanism which differentiates and transforms signals received through two or more ocelli, light perceived via the most ventral ocellus (No. 1) being the most important signal.An additional extraocular light receptor appears to be located dorsally in the head. This extraocular receptor can discriminate between different spectral ranges and perceive a brightness contrast (if the ocelli are blinded and the trunk is exposed to white illumination).     

Effects of temperature and tick weight on expression of autogeny in the argasid tick Ornithodoros parkeri Cooley (acari: Argasidae)

The effects of different temperatures on the expression of autogenic development in unfed/mated Ornithodoros parkeri Cooley females were examined. High temperature (29 C) induced autogeny in lower, middle and higher weight classes (11-20, 21-30, 31-40 mg, respectively) with all females in the highest weight class and most in the middle weight class ovipositing within 51 days post-mate. At a lower temperature (21 C) autogenic development was not expressed by higher and middle weight females, whereas lower weight females exhibited similar degrees of autogeny at both temperatures. Results are discussed in relation to presumptive factors involved in the control and mediation of autogeny.     

Rhodnius prolixus vitellogenesis: Dependence upon the blood source

The haemolymph-protein patterns of a Rhodnius prolixus colony, fed on human blood and of a colony fed on sheep blood, were compared by SDS-PAGE analysis. The vitellogenin-polypeptide patterns of larvae and females of both colonies were similar. However, males of the human-blood-fed colony had levels of circulating vitellogenin comparable to those of females, while males of the colony fed on sheep blood had only residual vitellogenin levels. The effect of human blood on different instars of a colony fed on sheep blood was examined. Autogeny occurs in the colony fed on human blood but not on that fed on sheep blood. When 5th-instar females from the sheep-blood-fed colony were fed on human blood, the phenomenon of autogeny was not displayed after moulting to the adult stage. Fourth-instar larvae from the colony fed on sheep blood however showed autogeny in the adult stage when fed on human blood from the 4th-instar on or in this stage only. Furthermore, first-cycle oviposition and the percentage moulting to the adult stage were increased in these groups.     

The evolution of peafowl and other taxa with ocelli (eyespots): a phylogenomic approach

The most striking feature of peafowl (Pavo) is the males'' elaborate train, which exhibits ocelli (ornamental eyespots) that are under sexual selection. Two additional genera within the Phasianidae (Polyplectron and Argusianus) exhibit ocelli, but the appearance and location of these ornamental eyespots exhibit substantial variation among these genera, raising the question of whether ocelli are homologous. Within Polyplectron, ocelli are ancestral, suggesting ocelli may have evolved even earlier, prior to the divergence among genera. However, it remains unclear whether Pavo, Polyplectron and Argusianus form a monophyletic clade in which ocelli evolved once. We estimated the phylogeny of the ocellated species using sequences from 1966 ultraconserved elements (UCEs) and three mitochondrial regions. The three ocellated genera did form a strongly supported clade, but each ocellated genus was sister to at least one genus without ocelli. Indeed, Polyplectron and Galloperdix, a genus not previously suggested to be related to any ocellated taxon, were sister genera. The close relationship between taxa with and without ocelli suggests multiple gains or losses. Independent gains, possibly reflecting a pre-existing bias for eye-like structures among females and/or the existence of a simple mutational pathway for the origin of ocelli, appears to be the most likely explanation.     

Laboratory adaptation of Bactrocera tryoni (Diptera: Tephritidae) decreases mating age and increases protein consumption and number of eggs produced per milligram of protein

A significant reduction in age of mating occurred during the first four generations (G1-G4) of laboratory adaptation of wild Bactrocera tryoni (Froggatt) and this was associated with the earlier attainment of peak egg load although no significant differences were detected in the peak egg load itself. A long term laboratory (LTL) strain had a significantly earlier mating age and higher peak egg load than flies of wild origin or those from the first four laboratory generations. The amount of protein consumed by females in the first week of adult life was significantly higher in the LTL strain than in flies of wild origin or G1-G4 but there were no significant changes (or only slight changes) with laboratory adaptation in the amounts of protein consumed up to the ages of mating and peak egg load. Laboratory adaptation resulted in no significant changes in egg size, egg dry weight, puparial fresh weight and the dry weight of newly emerged females. The large increase in fecundity with laboratory adaptation is associated with a 4- to 5-fold increase in the rate of conversion of dietary protein to eggs (i.e. eggs produced per mg of protein consumed).     

Stabilization of mineralized and sclerotized puparial cuticle of muscid flies

Calcium, magnesium and phosphorus are the major mineral elements in puparial exuviae of the face fly, Musca autumnalis, house fly, M. domestica and stable fly, Stomoxys calcitrans, but they are 20–50 times more prevalent in face fly than in the other two species that sclerotize the puparium. Carbon and nitrogen are approx. 5 times more abundant in house fly puparia than in face fly puparia. Face fly puparia contain two and three-fold less total amino acids than the house fly and stable fly, respectively. β-Alanine is a major amino acid in puparial cuticle of the house fly and stable fly, but it is absent in the face fly. There is no significant difference in glucosamine (chitin) content between the three species. Dopamine is the major catechol detected in face fly puparial cuticle while N-β-alanyldopamine (NBAD) is 10 to 15 times more prevalent than other catechols such as dopamine, N-acetyldopamine (NADA), 3,4-dihydroxyphenylalanine (DOPA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in house fly and stable fly puparial cuticles. The latter two species have 75 to nearly 200 times higher levels of extractable catechols than the face fly. At the onset of pupariation, dopamine and NBAD attain nearly equivalent titres in puparial cuticles of face fly and house fly, respectively. Dopamine subsequently decreases more than 40-fold in the face fly as the cuticle becomes stabilized, while NBAD continues to accumulate in the house fly. The house fly covalently incorporates about 150 times more catechols in the puparium than does the face fly. The force required to fracture house fly and stable fly puparia is about three-fold greater than that required to fracture face fly puparia of comparable thickness. However, the face fly puparium attains a strength comparable to those of house fly and stable fly puparia by significantly increasing its thickness. These results demonstrate that dipterans use both catecholamines and minerals for stabilization of puparial cuticle with the house fly and stable fly relying primarily on sclerotization and the face fly on mineralization.     

Diapausing pupae of the flesh fly Sarcophaga crassipalpis (Diptera: Sarcophagidae) are more resistant to inoculative freezing than non-diapausing pupae

The resistance of diapausing (overwintering) and non‐diapausing (summer) Sarcophaga crassipalpis (Diptera: Sarcophagidae) pupae to inoculative freezing was examined. Although both types of pupae resisted inoculative freezing after 24‐h submergence in water, diapausing pupae were overall significantly more resistant than non‐diapausing pupae. Exposing the thin pupal cuticle by removing the ends of the puparial case eliminated the capacity of both pupal types to resist inoculative freezing, indicating that resistance to inoculative freezing resides with the puparium. Pupae submerged in surfactant solution were significantly less resistant to inoculative freezing than those submerged in water. Furthermore, the puparial water content of pupae submerged in surfactant solution was significantly greater than that of puparia from pupae submerged in water. Surfactant may have promoted inoculative freezing by facilitating the spread of water over the surface of and into the puparium, thereby creating bridges between external ice and pupal body fluids. Extracting puparial surface lipids with chloroform/methanol (2 : 1, v:v) decreased the resistance of non‐diapausing pupae to inoculative freezing but did not significantly affect that of diapausing pupae. This finding indicates that the puparium of diapausing pupae contains protection against inoculative freezing separate from its surface lipids. This barrier may be important in protecting the freezing‐intolerant overwintering pupae against inoculative freezing within their soil hibernaculum.     

Repair of damage induced by ultraviolet light in DNA polymerase-defective Escherichia coli cells

Cells of the Escherichia coli mutant polA1, which lack DNA polymerase activity in vitro, are four times as sensitive as wild-type to ultraviolet irradiation. Cells of the mutant uvrA6, which are unable to excise dimers, are 12 times as sensitive as wild-type. We have shown that the double mutant polA1 uvrA6 is only slightly more sensitive to u.v. than the uvrA6 single mutant and conclude, therefore, that the u.v. sensitivity associated with the defect in DNA polymerase is primarily the result of a reduction in the efficiency of the excision-repair pathway. Observations on the effect of u.v. irradiation on the ability of polA1 cells to support the growth of phage λ suggest that the post-u.v. repair function of polymerase is subsequent to the action of the uvr⁺ gene products. Evidence is presented that the recA repair system is involved in excision-repair in polA1 cells, and we propose that it can substitute for DNA polymerase in repairing the gaps produced by dimer excision. This would account for the relatively slight effect of the polA1 mutation on u.v. sensitivity.     

Indirect SOS induction is promoted by ultraviolet light-damaged miniF and requires the miniF lynA locus

Indirect prophage induction is produced by transfer to recipients of u.v.-damaged F plasmid (95 kb). We tested whether the SOS signal can be produced by miniF, a 9.3 kb restriction fragment, coding for the replication and segregation functions of plasmid F. We used λminiF, a hybrid phage-plasmid. u.v.-irradiated λminiF induced prophages φ80 or λ and sfiA, a chromosomal SOS gene, in more than 50% of the infected cells. The maximal inducing dose produced about 0.5 pyrimidine dimers per kb and left 1% of λminiF survivors. Thus, the SOS signal produced by u.v.-damaged λminiF was almost as potent as that resulting from direct u.v.-irradiation of the lysogens. The u.v.-damaged vector λ, devoid of miniF, failed to promote SOS induction. In contrast, efficient induction was observed when u.v.-damaged λminiF infected a λ immune host, in which replication and expression of the phage genome were repressed. When replication and expression of the miniF genome was repressed by Hfr incompatibility, SOS induction was largely prevented. All these facts indicate that, in the hybrid λ-miniF, it is the u.v.-damaged miniF that generates an SOS signal.To locate on the miniF genome the loci that are involved in the production of the SOS signal, we isolated deletions spanning all the miniF restriction fragments. We characterized six mutant phenotypes (Par⁺, Rep^?, Fid^?, Par-2, Par-1 and SOS^?) related to four functions; partition, copy number, replication and SOS induction. A locus, we call lynA, 800bp long, located by deletion mapping between the two origins of replication oriP and oriS is required for the production of an inducing signal.We postulate that indirect SOS induction by u.v.-damaged miniF results from the disturbance of the lynA function that may be involved in the co-segregation of F plasmid with the host chromosome.     

Homothorax controls a binary Rhodopsin switch in Drosophila ocelli

Visual perception of the environment is mediated by specialized photoreceptor (PR) neurons of the eye. Each PR expresses photosensitive opsins, which are activated by a particular wavelength of light. In most insects, the visual system comprises a pair of compound eyes that are mainly associated with motion, color or polarized light detection, and a triplet of ocelli that are thought to be critical during flight to detect horizon and movements. It is widely believed that the evolutionary diversification of compound eye and ocelli in insects occurred from an ancestral visual organ around 500 million years ago. Concurrently, opsin genes were also duplicated to provide distinct spectral sensitivities to different PRs of compound eye and ocelli. In the fruit fly Drosophila melanogaster, Rhodopsin1 (Rh1) and Rh2 are closely related opsins that originated from the duplication of a single ancestral gene. However, in the visual organs, Rh2 is uniquely expressed in ocelli whereas Rh1 is uniquely expressed in outer PRs of the compound eye. It is currently unknown how this differential expression of Rh1 and Rh2 in the two visual organs is controlled to provide unique spectral sensitivities to ocelli and compound eyes. Here, we show that Homothorax (Hth) is expressed in ocelli and confers proper rhodopsin expression. We find that Hth controls a binary Rhodopsin switch in ocelli to promote Rh2 expression and repress Rh1 expression. Genetic and molecular analysis of rh1 and rh2 supports that Hth acts through their promoters to regulate Rhodopsin expression in the ocelli. Finally, we also show that when ectopically expressed in the retina, hth is sufficient to induce Rh2 expression only at the outer PRs in a cell autonomous manner. We therefore propose that the diversification of rhodpsins in the ocelli and retinal outer PRs occurred by duplication of an ancestral gene, which is under the control of Homothorax.