Fate of mouse carcasses in a Northern Woodland

1. Small, vertebrate carrion is a significant input into terrestrial ecosystems. The relative importance of different recyclers of carrion is poorly understood because of seasonal and habitat variation and methodological differences among studies. Many studies, in particular, do not account adequately for the activity of burying beetles (Nicrophorus spp.). 2. The present work, utilising a previously unstudied woodland, addresses this concern by: placing only two carcasses in the field at one time, using microsites only once, and providing a means to easily recover successful burying beetles. 3. Burying beetles buried 77.5% of experimental mouse carcasses over their breeding season, and typically did so within three activity periods after placement (30 of 31 burials). 4. The results and a brief review suggest that burying beetles are the dominant summer competitor for small, vertebrate carrion in mid‐ and northern latitude woodlands. Information on the age of carcasses utilised by burying beetles also provides an ecological context for laboratory studies of behaviour, life history, and microbial interactions.     

Effects of larval competition on survival and growth in Mediterranean fruit flies

1. Larval success was compared when one, two, or three egg clutches were laid in kumquat fruits (≈ 10 ml in volume) either successively on the same day or at the rate of one clutch per day. 2. Increased clutch density was associated with a significant decrease in larval survival rate and non‐significant decreases in larval growth rate and pupal mass. 3. Larval and pupal parameters showed significantly larger variance when clutches were laid on successive days than on the same day, suggesting a competitive advantage for older larvae over younger larvae. 4. The results suggest that, in small fruit, reduced fitness due to larval competition may act against possible fitness benefits due to social facilitation among adult females, hence reducing the likelihood of non‐linear population dynamics caused by processes such as the Allee effect.     

Dynamic information and host acceptance by a tephritid fruit fly

Abstract. 1. Female apple maggot (Rhagoletis pomonella Walsh) flies held in field cages usually oviposited in an unparasitized (non-pheromone marked) fruit when it was encountered.
2. Oviposition in a previously parasitized (pheromone marked) fruit depended upon the time since the last oviposition (TSLO) and the percentage of infested fruit encountered during search for oviposition sites.
3. Previous theories of host acceptance suggest that the acceptance or rejection of a host should depend dichotomously on time since last oviposition and the fraction of marked hosts in the last five encounters. The experiments, however, show considerable variability and are thus not consistent with the theory.
4. A new theory for the experiments is introduced. This model involves physiological (egg complement) and informational state variables and leads to intuitive understanding of the experimental results. In particular, the model shows how the plasticity in oviposition site selection may arise from fitness maximizing behaviour. Alternative models are also discussed. All of the models stress the importance of physiological and informational states.     

Condition and fate of larvae from insecticide-treated female tsetse flies Glossina palpalis

Many larvae from wild-caught female Glossina palpalis palpalis R.-D. treated topically with dieldrin or sumicidin or sumithrin or permethrin failed to pupariate and many larvae from mothers treated with sumicidin or sumithrin or neopynamin formed small or malformed puparia which failed to eclode. Puparia produced soon after maternal handling often did not emerge and many produced by flies starved more than 3 days also did not emerge. Very many puparia from dieldrin-treated mothers failed to emerge and non-emergence was common for puparia from flies treated with endosulfan or sumithrin or deltamethrin. Non-emerging puparia were produced soon after pyrethroid-treatment, probably due to effects on larval integumentand muscles, but were produced later after organochlorine-treatment, due to ingestion of insecticide by larvae while in utero.

---

Résumé Les expériences ont porté sur des femelles sauvages de Glossina palpalis palpalis R.D. capturées dans la nature. Les comparaisons ont porté sur l'état et les performances de lots de pupes provenant de mouches non-traitées et de larves mûres traitées localement avec de l'acétone (témoin) ou avec 14 insecticides différents.Toutes les larves témoin se sont nymphosées, mais le taux d'échec augmentait avec la diéldrine, la sumicidine, la sumithrine et la permethrine. Les pupes anormales (petites ou déformées) étaient plus nombreuses dans le lot témoin que dans le lot non-traité, et les fréquences étaient plus élevées que chez le témoin avec la sumidicine, la sumithrine et la néopynamine.Seulement 3 mouches sont issues de 107 pupes anormales; il n'y a eu aucune éclosion pour 28% des pupes du lot témoin contre 15% pour le lot non-traité. Pour le témoin le taux d'émergence était faible dans les pupes formées le premier jour (jour du traitement), par suite de la manipulation maternelle; il n'a pas augmenté jours 2 et 3, mais a diminué par la suite à cause du jeûne in utero. Les doses élevées de tous les insecticides réduisent plus les émergences que les doses faibles. Les organophosphates et le propoxur ne limitent pas les émergences, mais elles sont réduites par l'endosulfane, la sumithrine et la deltaméthrine, et très fortement par la diéldrine. Les pupes stériles ont été surtout formées dès le traitement aux pyréthroïdes (jour 1); et surtout plus tard (jours 2 et 3) lors des traitements aux organochlorés. L'ingestion par la larve in utero de grandes quantités d'insecticides pendant les 3 jours précédant la parturition était la principale cause de mortalité, et aussi de la forte tolérance aux organochlorés des femelles prégnantes. Les effets de pyréthroïdes sur l'activité musculaire réduisent aussi les émergences.Aucune mouche ne s'est alimentée après les traitements.

     

Rate of trypanosome killing by lectins in midguts of different species and strains of Glossina

The activity of lectins in different species of tsetse was compared in vivo by the time taken to remove all trypanosomes from the midgut following an infective feed and in vitro by agglutination tests. Teneral male Glossina pallidipes Austen, G. austeni Newstead and G. p. palpalis R-D. removed 50% of all Trypanosoma brucei rhodesiense Stephens & Fantham infections within 60 h. A 'refractory' line of G. m. morsitans Westwood took 170 h to kill 50% infections while a 'susceptible' line of the same species failed to kill 50%. Agglutination tests with midgut homogenates showed differences between fly stocks which accorded with differences in rate of trypanosome killing in vivo. Flies fed before an infective feed were able to remove trypanosomes from their midguts more quickly than flies infected as tenerals. Increasing the period of starvation before infection increased the susceptibility to trypanosome infection of non-teneral flies. Teneral flies showed little agglutinating activity in vitro, suggesting that lectin is produced in response to the bloodmeal. Feeding flies before infection also abolished the differences in rate of trypanosome killing found between teneral 'susceptible' and 'refractory' G. m. morsitans, suggesting that maternally inherited susceptibility to trypanosome infection is a phenomenon limited to teneral flies. Electron micrographs of midguts of G. m. morsitans suggest that procyclic trypanosomes are killed by cell lysis, presumably the result of membrane damage caused by lectin action.     

Feeding postures of suspension-feeding larval black flies: the conflicting demands of drag and food acquisition

Summary We tested whether larval black flies actively control the positioning of their feeding appendages (labral fans), and if so, whether their posture represents a balance between the conflicting demands of drag and feeding. We compared the postures of live larvae with the postures of larvae killed by heat-shock in three different flow regimes in a laboratory experiment; we assumed that the postures of heat-killed larvae approximated a passive response to drag. The average height of the labral fans above the bed declined significantly in faster flows, and was significantly greater in live than dead larvae. There was also a significant interaction effect, since the difference between the fan heights of live and dead larvae was greater in slower flows. Two mechanisms may contribute to this result. Larvae in slower flows have to increase their fan heights more than larvae living in faster flows to achieve comparable increases in velocity and thus particle flux. In addition, muscular strength may limit the feeding postures larvae can assume. The fan heights of live larvae also varied depending on the concentration of food particles: larvae exposed to low food concentrations held their fans higher above the bed than did larvae exposed to high food concentrations in the same flow regime. This change in posture is due neither to an uneven particle concentration in the boundary layer nor to added drag from particles trapped in the labral fans. Collectively, our results indicate that these suspension feeders actively control their feeding posture, and suggest that these varying postures represent a dynamic balance between the conflicting needs of minimizing drag and maximizing feeding.     

Cold shock and heat shock: a comparison of the protection generated by brief pretreatment at less severe temperatures

Abstract Brief exposure to low (0^oC) or high (40^oC) temperature elicits a protective response that prevents injury when the flesh fly, Sarcophaga crassipalpis Macquart, is subjected to more severe cold (-10^oC) or heat (45^oC). Both the low and high temperature responses were found in all developmental stages of the fly, but were most pronounced in the pupal and pharate adult stages. The protective responses generated by brief exposure to 0 or 40^oC appear similar in that both result in a rapid acquisition of cold or heat tolerance and a loss of protection after the flies are returned to 25^oC. The protection generated by chilling is obvious within 10 min of exposure to 0^oC while a 30 min exposure to 40^oC is required to induce the high temperature protection. High temperature protects against cold shock injury within a narrow range (around 36^oC) but we have no evidence that low temperature can protect against heat injury. We previously demonstrated that the rapid increase in cold tolerance correlates with concomitant increases in glycerol concentration, but in this study we found no significant elevation in glycerol in heat-shocked flies. Thus the physiological and biochemical bases for the rapid responses to cold and heat appear to be different.     

Preference for plants damaged by conspecific larvae in ovipositing cabbage root flies: influence of stimuli from leaf surface and roots

In laboratory dual-choice assays females of the cabbage root fly, Delia radicum, prefer for oviposition plants with roots damaged by conspecific larvae to undamaged controls. Cauliflower and kale plants were inoculated with root fly eggs (25 per plant) and the hatching larvae were allowed to feed on the roots for various periods of time (1–17 days). After 4 (cauliflower) or 5 (kale) days of larval feeding the oviposition preference was most pronounced and flies laid between 64% and 68% of their eggs near plants with damaged roots. Later, with increasing damage but fewer surviving, and thus actively feeding, larvae, the magnitude of the preference declined. The preference for plants already damaged by conspecific larvae may contribute to the previously observed aggregated distribution of D. radicum eggs in Brassica crop fields.Further experiments revealed that the sensory cues inducing this oviposition preference originate from the complex consisting of the damaged roots, the surrounding substrate (soil) and associated microbes, rather than from the aerial plant parts. In choice assays using the root-substrate complex of damaged and control plants (aerial parts removed), the observed preference for damaged roots was similar to that found for the entire plant but was more pronounced. The damaged roots alone, compared to control roots, received up to 72% (cauliflower) and 75% (kale) of the eggs. By contrast, surrogate leaves sprayed with methanolic leaf surface extracts from the most preferred plants which had been damaged were not discriminated from surrogate leaved sprayed with extracts of the respective control plants. Analysis of glucosinolate levels in methanolic leaf surface extracts revealed that root damage resulted in enhanced concentrations of indole-glucosinolates on the leaf surface in kale but not in cauliflower. Although indole-glucosinolates are oviposition stimulants for the cabbage root fly, the induced changes were apparently too small to influence oviposition behaviour.     

Effects of fruit fly host, fruit species, and host egg to female parasitoid ratio on the laboratory rearing of Biosteres arisanus

The host suitability of the oriental fruit fly, Bactrocera dorsalis (Hendel), for development of Biosteres arisanus (Sonan), a braconid parasitoid, was compared with three other fruit fly species, namely, Mediterranean fruit fly, Ceratitis capitata Weidemann, melon fly, Bactrocera cucurbitae Coquilett, and Malaysian fruit fly, Bactrocera latifrons (Hendel). In addition, effects of five different fruit species, namely, Carica papaya L. (solo papaya), Musa sapientum (L.) O. Ktze. (apple banana), Mangifera indica (L.) (Haden mango), Terminalia catappa (L.) (false kamani), and Citrus aurantiifolia (Christman) Swingle (common lime), on the parasitization rate of B. dorsalis and sex ratio of parasitoid progenies were evaluated. Effects of host egg to female B. arisanus ratios on parasitoid progeny yields were likewise determined. The host suitability of fruit flies for development of B. arisanus was ranked as: B. dorsalis>C. capitata=B. latifrons=B. cucurbitae. Based on percent parasitization of B. dorsalis, preference of B. arisanus females for host eggs varied with fruit species, however, preferential oviposition displayed by female parasitoids did not influence sex ratios of subsequent parasitoid progenies. Increases in host egg to female parasitoid ratios of 5:1, 10:1, 20:1, 25:1, and 30:1 corresponded with increases in parasitoid progeny yield reaching a plateau at 20:1.