The flight and landing of tsetse (Glossina) in response to components of host odour in the field

ABSTRACT. Studies were conducted in Zimbabwe of the responses of Glossina morsitans morsitans Westwood and Glossina pallidipes Austen to various host odours using either arrangements of electrocuting nets or visual observations. Tsetse flying upwind in a plume of carbon dioxide, acetone and octenol turned downwind upon flying into a plume of acetone or octenol, but did not turn upon flying into a plume of carbon dioxide. They also turned in response to a transient decline in odour concentration. Tsetse landed on the ground in the vicinity of a source of natural odour or artificial odour containing carbon dioxide but not at sources of acetone or octenol only. The proportion of female G.pallidipes caught at a source of natural odour (37%) was significantly different from that caught at a source of synthetic odour (17%). Resting tsetse stimulated by natural odour took off sooner than non-stimulated flies and had a strong upwind bias in the direction of take off. Tsetse stimulated with artificial odour did not take off sooner than non-stimulated flies. It is suggested that there is an unidentified components) of ox odour that activates resting tsetse.     

Host Status of Five Weed Species and Their Effects on Pratylenchus zeae Infestation of Maize

The host suitability of five of the most common weed species occurring in maize (Zea mays L.) fields in South Africa to Pratylenchus zeae was tested. Based on the number of nematodes per root unit, mealie crotalaria (Crotalaria sphaerocarpa) was a good host; goose grass (Eleusine indica), common pigweed (Amaranthus hybridus), and thorn apple (Datura stramonium) were moderate hosts; and khaki weed (Tagetes minuta) was a poor host. Only the root residues of khaki weed suppressed the P. zeae infestation of subsequently grown maize. When goose grass, khaki weed, and mealie crotalaria were grown in association with maize in soil infested with P. zeae, goose grass and khaki weed severely suppressed maize root development; this resulted in a low number of nematodes per maize root system and a high number of nematodes per maize root unit. Mealie crotalaria did not restrict maize root growth and did not affect nematode densities per maize root system or maize root unit. Special attention should be given to the control of mealie crotalaria, which is a good host for P. zeae, and goose grass, which, in addition to its ability to compete with maize, is also a suitable host for P. zeae.     

Meloidogyne mayaguensis n. sp. (Meloidogynidae), a Root-knot Nematode from Puerto Rico

Meloidogyne mayaguensis n. sp. is described and illustrated from specimens obtained from galled roots of eggplant, Solanum melongena L., from Puerto Rico. The perineal pattern of females is round to ovoid with fine, widely spaced striae. It has occasional breaks of striation laterally and a circular tail tip area lacking striae. The stylet, 15.8 μm long, has reniform knobs that merge gradually with the stylet shaft. Males have a high, rectangular, smooth head region, not set off from the body contour. The labial disc is continuous with the medial lips which do not slope posteriorly. The styler, 22.9 μm long, has large rounded backward sloping knobs; the shaft is of uneven diameter. Mean body length of second-stage juveniles is 453.6 μm. The truncate head region is not annulated, and the rounded, slightly raised labial disc and the crescentic medial lips form dumbbell-shaped lip structures. The stylet, 11.6 μm long, has rounded, posteriorly sloping knobs. The slender tail, 54.4 μm long, gradually tapers to a bluntly pointed tip. Tomato, tobacco, pepper, and watermelon are good hosts; cotton and peanut are not hosts. M. mayaguensis n. sp. reproduces by mitotic parthenogenesis and has a somatic chromosome number of 2n = 44-45. The enzyme patterns are unique among Meloidogyne species.     

Bacteriophage lambda DNA packaging: A mutant terminase that is independent of integration host factor

Summary ⁺ is able to grow in Escherichia coli cells lacking integration host factor (IHF), producing a burst of approximately 25% that produced in IHF⁺ cells. In vitro, however, we find that the DNA packaging enzyme terminase is strongly dependent on IHF in both cos cleavage reactions and DNA packaging reactions. The cos59 mutation renders dependent on IHF in vivo. The cos59 mutation is a deletion of 3 base pairs at the XmnI site in the cohesive end site (cos) of . Variants of cos59 that were able to grow in the absence of IHF were isolated and found to carry a mutation, called ms1, in the Nu1 gene, which codes for the small subunit of terminase. The Nu1ms1 mutation results in a change of the 40th amino acid of the Nu1 gene product from leucine to phenylalanine. The Nu1ms1 terminase was independent of IHF in packaging reactions in vitro. The results indicate that the mutation either renders terminase: (1) able to utilize some host protein other than IHF, or (2) totally independent of host factors.     

Host range differentiation of spore-positive and spore-negative strain types of Frankia in stands of Alnus glutinosa and Alnus incana in Finland

Host compatibility of different spore-positive (Sp⁺)and spore-negative (Sp^?) strain types of Frankia from alder stands in Finland was studied in Modulation tests with hydrocultures of Alnus glutinosa (L.) Gaertner, A. incana (L.) Moench and A. nitida Endl. Root nodules and soil samples from stands of A. incana (Lammi forest and Hämeenlinna forest) were dominated by Sp ⁺ types of Frankia (coded AiSp⁺ and AiSp⁺ H. respectively), which caused effective root nodules in test plants of A. incana, but failed to induce nodules in A. nitida. In A. glutinosa Frankia strain types AiSp ⁺ and AiSp ⁺ H caused small, ineffective root nodules with sporangia (coded Ineff ^?), which were recognized by the absence or near absence of vesicles in the nodule tissue. Ineffective nodules without sporangia (coded Ineff ^?) were induced on A. glutinosa with soil samples collected at Lammi swamp. The spore-negative strain type of Frankia was common in root nodules of A. glutinosa in Finland (Lammi swamp) and caused effective Sp^? type root nodules (coded AgSp ^?) in hydrocultures of A. incana, A. glutinosa and A. nitida. A different Sp ⁺ strain type of Frankia. coded AgSp⁺ Finland, was occasionally found in stands of A. glutinosa. It was clearly distinguished from strain type AiSp ⁺ by the ability to produce effective nodules on both A. glutinosa and A. incana. The nodulation capacities of soil and nodule samples were calculated from the nodulation response in hydrocutlure and served as a measure for the population density of infective Frankia particles. Sp ⁺ nodules from both strain types had equal and high nodulation capacities with compatible host species. The nodulation capacities of Sp type root nodules from A. glutinosa were consistently low. High frequencies of Frankia AiSp⁺ and AiSp⁺ H were found in the soil environment of dominant AiSp ⁺ nodule populations on A. incana. The numbers of infective particles of this strain type were insignificant in the soil environment of nearby Sp ^? nodule populations on A. glutinosa and in the former field at Hämeen-linna near the Sp⁺ nodule area in Hämeenlinna forest. Strain type AgSp^? had low undulation capacity in the soil environment of both A. incana and A. glutinosa stands, Explanations for the strong associations between Frankia strain types AiSp⁺ and AiSp ^? H and A. incana and between strain type AgSp^? and A. glutinosa are discussed in the light of host specificity and of some characteristics of population dynamics of both strain types. The possible need to adapt the concept of Frankia strain types Sp ⁺ and Sp ^? to strains with some variation in spore development was stressed by the low potentials of strain type AiSp ⁺ H to develop spores in symbioses with hydrocultures of A. incnna.     

蚤数量与宿主数量关系

无论在自然条件下或在人为条件下,蚤指数和染蚤率的高低与宿主密度的高低是一致的.宿主密度的升降,会导致其寄生蚤指数和染蚤率的升降. 本文讨论了宿主数量下降导致其寄生蚤数量下降的原因,仅是分析推测,提出几方面的看法.     

Effects of early adult experience on host selection in insects: Some experimental and theoretical results

A field experiment with Drosophila melanogasterrevealed that when flies encounter a particular food type soon after emergence, the probability of their subsequently being attracted to such a resource is increased. In this experiment, the length of time flies experienced their postemergence environments was under the control of the flies themselves. The experiment thus realistically mimicked one form of experiential effect that may be important in nature. A theoretical model is developed which shows that enhanced adult preferences for the types of resources fed on as larvae can substantially increase the degree of host-based genetic subdivision within a polyphagous population.     

Plant wound compounds from oviposition scars used in host discrimination by a stem-galling sawfly

The stem-galling sawfly Euura lasiolepisuses one or more plant wound compounds resulting from oviposition scars as cues in host discrimination (avoiding sites occupied by conspecifics). Four experiments were conducted to test hypotheses about how Euurapartitions resources. Experiment 1 demonstrated that Euuraavoids ovipositing on nodes with scars from previous ovipositions. Experiment 2 showed no evidence that the sawfly uses oviposition-deterring pheromones and indicated there is a time lag following oviposition before the oviposition scar becomes a deterrent. Experiment 3 showed that sawflies avoid artificially formed scars, demonstrating that a plant cue alone can lead to host discrimination. Experiment 4 showed that visual or tactile cues are not necessary for host discrimination and indicated that a plant wound compound functions as an oviposition deterrent. Both experimental results and field surveys showed that Euuraoviposition scars were more uniformly distributed than expected if sawflies were ignoring previous ovipositions.     

Covariance of adult size and development time in the parasitoid waspAphidius ervi in relation to the size of its host,Acyrthosiphon pisum

Summary Adult size (in terms of dry weight; DW) and development time (T _p ) of the solitary parasitoidAphidius ervi varied when reared in different nymphal instars of its host, apterous virginoparae of the pea aphid (Acyrthosiphon pisum). Parasitoid DW increased with an increase in the DW of the host at parasitization, from the first to the third aphid instar. Female wasps gained 1.1 times more in DW than their male counterparts in all four host classes, butT _p did not significantly differ between the sexes. Parasitoid DW was consistently more variable thanT _p . The two traits covaried positively with an increase in host size from the first to the third instar, but they varied independently in parasitoids from fourth-instar hosts. The host size (and stage) at the time of parasitization imposes constraints on the growth and development of immatureA. ervi that are reflected in the pattern of covariation between DW andT _p . When growing in aphids below a certain size threshold, parasitoids can maximize fitness by a trade-off between DW andT _p . Consequently, the assumption implicit in host-size models of parasitoid oviposition decisions — that females incur a relatively greater reduction in size (used as an index of fecundity) than males when developing in poor quality hosts — can be falsified.     

The time and egg budget of Leptopilina clavipes, a parasitoid of larval Drosophila

Abstract.

• 1 For the understanding of the influence of natural selection on the persistence of host selection behaviour in populations of Drosophila parasitoids it is important to know whether parasitoids will become time- or egg-limited. We investigated whether the Drosophila parasitoid Leptopilina clavipes (Hartig) meets egg- or time-limited conditions in the field.
• 2 To this end the following aspects of the parasitoid's life were studied: egg load at emergence, travelling velocity between patches, patch residence times, oviposition rates and life expectancy. Together with the results from earlier studies on host and patch distributions, this formed the input of a ‘Monte Carlo’ simulation model, in which the life history of an individual parasitoid can be traced.
• 3 The simulations revealed that under the conditions found in the field 12.9% of the parasitoid population is egg-limited. The model was also run for a number of scenarios which reflect ‘good’ or ‘bad’ circumstances. In most cases a significant proportion of the parasitoid population proved to be egg-limited.
• 4 For the measurement of travelling velocities and patch residence times a marking method, especially applicable to small-sized parasitoids such as L.clavipes, is described. Marking did not affect survival, host habitat location or host detection rate. Parasitoids were found to be attracted to the odour of fruit-bodies of Phallus impudicus, the most important breeding substrate of their hosts.