Parasitoid behaviour: predicting field from laboratory

Abstract.  1. Most of what is known about parasitoid behaviour comes from laboratory observations: field quantitative observations on searching parasitoids are extremely difficult to do and are rare. The basic components of Aphytis melinus 's response to California red scale ( Aonidiella aurantii ) were studied in the laboratory: encounter, rejection, drumming, probing, oviposition, and host-feeding. It was then asked whether these observations provided a reliable guide to behaviour in the field in a situation that was very different from the laboratory.
2. Field observations were carried out on bark on the trunk and interior branches of trees where live scale density is extremely high in patches, dead scale make up 90% of all scale, and could be expected to interfere with Aphytis search.
3. The laboratory observations predicted well the time taken in the field for each basic event (drumming or probing) and average times spent on a scale. Also well predicted were the distributions of times spent on drumming, probing, and total time on a scale. Rejection rates were much higher in the field. Thus, the laboratory studies predicted foraging behaviour in the field with variable success; potential explanations for observed mismatch between laboratory and field and its possible larger implications are discussed.     

Relationships among pure cultured strains of Frankia based on host specificity

Fifty strains of Frankia were tested for their ability to nodulate six species of actinorhizal plants. Pure cultured strains were used to inoculate seedlings of Alnus glutinosa (L.) Gaertn., Alnus rubra Bong., Casuarina equisetifolia L., Elaeagnus angustifolia L., Hippophaë rhamnoides L. and Myrica cerifera L. in nutrient solution culture. From the results of this study, host inoculation groups among the actinorhizal plants were defined. Although overlap between host inoculation groups appears to be common, the results from this study did not support the view that Frankia strains are promiscuous. All Frankia strains tested in this study could easily be classified into four major host-specificity groups.     

Limnology of a hypertrophic reservoir storing wastewater effluent for agriculture at Kibbutz Na'an,Israel

The reservoir investigated collects domestic and agricultural effluents after primary and secondary treatment. Despite the high concentration of organic matter (mean BOD⁵ = 60 mg l^–1), the reservoir does not deteriorate to produce obnoxious, anaerobic conditions. During a one year period, dissolved oxygen levels fluctuated widely but presented a long term dynamic stability, based on diffusion from the air during the winter mixing and on algal — bacterial — zooplankton equilibrium during the summer stagnation. The system, rich in organic and inorganic nutrients exhibited a much higher self-regulatory cability, than would be expected from its extreme enrichment. A hypothesis is proposed to explain the dynamic equilibrium achieved under extremely hypertrophic conditions.Human Environmental Sciences Division, School of Applied Science and Technology     

Effect of rainstorms on heterotrophic bacterial activity in a hypertrophic African lake

Hartbeespoort Dam is a hypertrophic man-made lake which is located in the Transvaal Province of South Africa. This region has recently experienced its most severe drought of the century. However, on three occasions in the summer rainy seasons of 1984 and 1985, major rainfalls (> 50 mm) occurred which caused large inflows to the lake. Inflowing river water entered as a density current causing marked silting of the water. Within the epilimnion (0–10 m) prior to these rainfalls there was usually no variation of bacterial numbers with depth, but heterotrophic bacterial activity (glucose uptake) decreased with depth concomitant with primary production. With the increased river inflow bacterial numbers did not increase but bacterial activity at the bottom of the epilimnion (10 m) increased to as high as 2.7 µg C l^–1 h^–1 in January 1985, reversing the depth profile of bacterial activity within the epilimnion. This resulted in decreased glucose concentrations (K_t + S_n) and turnover times. Heterotrophic activity per cell increased by between 2.5 and 5 times. These data demonstrate that storm events are important phenomena causing short-term changes in the metabolic activity of planktonic heterotrophic bacteria in lakes.     

Feeding responses to solanaceous allelochemicals by larvae of the tobacco hornworm, Manduca sexta

Feeding responses of the oligophagous tobacco hornworm to allelochemicals prevalent in their host plants were determined in food choice-tests using filter paper discs laced with a test solution or water (control). Six solanaceous alkaloids, tomatine, tomatidine, solanine, solanocapsine, atropine and nicotine, were tested and only tomatine and solanocapsine were found to influence preference behavior. Solanocapsine (5 mM) deters feeding whereas tomatine (1 mM) stimulates feeding slightly. No synergistic effect of either tomatine or tomatidine with sucrose was found.The responses to tomatine are affected by previous feeding experience. Tomatine slightly stimulates feeding in larvae reared on tomato (Lycopersicon esculentum), but slightly deters feeding in larvae reared on Jerusalem cherry (Solanum pseudocapsicum). Such induced preference is absent for the other alkaloids tested, which indicates that these alkaloids do not by themselves induce preferences for the plants containing them.The non-alkaloid allelochemicals, chlorogenic acid, rutin, and 2-tridecanone also influenced food choice behavior. Chlorogenic acid is slightly stimulatory at its natural concentration (1mM), but strongly deterrent at higher concentrations. Rutin stimulates feeding in a concentration-dependent manner. Its activity must be due to the glycosylated structure, because both the aglycone (quercetin) and the sugar moiety (rutinose) are neutral. Removal of the glucose part of rutin, as in quercitrin, results in feeding deterrent activity. 2-Tridecanone is neutral at its concentration in cultivated tomato (1 mM), but strongly deterrent and toxic at higher concentrations. Preference behavior is not affected by solanesol, GABA, and a mixture of host plant compounds stimulatory for anothe solanaceous-specific feeder, the Colorado potato beetle (Leptinotarsa decemlineata).We conclude that the prevalent solanaceous alkaloids and other allelochemicals tested do not play important roles in food selection of the tobacco hornworm, although some may make small contributions.

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Résumé Des experiences de choix de chenilles oligophages de M. sexta ont été réalisees avec des disques de papier filtre imbiles d'eau ou de solutions des substances allélochimiques dominantes dans les plantes consommées. Sur les six alcaloïdes de solanées examinés: tomatine, tomatidine, solanine, solanocapsine, atropine et nicotine, seuls la tomatine et la solanocapsine ont influé sur le choix; la solanocapsine (5 mM) empêche la prise de nourriture, tandis que la tomatine (1 mM) la stimule légèrement. Aucun effet synergique de la tomatine ou de la tomatidine n'a été observé en présence de sucrose.La réponse à la tomatine est modifiée par la prise de nourriture antérieure. Elle stimule légèrement l'alimentation de chenilles élevées sur tomates (Lycopersicon esculentum), mais dissuade légèrement les chenilles élevées sur Solanum pseudocapsicum. II n'y a pas d'action induite semblable avec les autres alcalïdes examinés, ce qui indique que ces alcaloïdes ne peuvent pas induire par eux-mêmes de préférences pour les plantes qui les contiennent.Des substances allélochimiques non-alcaloïdes: acide chlorogénique, rutine, et 2-tridécanone, influent aussi sur le comportement de choix alimentaire. L'acide chlorogénique est légèrement stimulant à sa concentration naturelle (1 mM), mais fortement dissuasif aux concentrations supérieures. La rutine stimule la prise de nourriture en fonction de sa concentration. Son activité doit être due à sa structure glucosylate, puisqu'aussi bien l'aglycone (quercitine) que la moiteé sucrée (rutinose) sont neutres. La suppression de la partie glucose de la rutine, comme dans le cas de la quercitine, a un effet dissuasif. A sa concentration dans la tomate cultivée (1 mM), le 2-tridécanone est neutre, mais il est fortement dissuasif et toxique à des concentrations supérieures.Le comportement de choix n'est pas modifié par le solanésol, le GABA, et par un mélange de composés végétaux stimulant un consommateur spécifique de solanées, comme le doryphore (Leptinotarsa decemlineata).Nous pouvons conclure que les principaux alcaloïdes et autres substances allélochimiques des solanées que nous avons examinés n'interviennent pas d'une façon importante, mais peuvent avoir une influence secondaire, dans les choix alimentaires de Manduca sexta.

     

Host preferences of two encyrtid parasitoids for the Columbian Phenacoccus spp. of cassava mealybugs

In a choice test among six life stages of Phenacoccus herreni Cox & Williams, Epidinocarsis diversicornis (Howard) used its antennae to examine adult and 3rd stadium females more than other stages and preferentially attempted to oviposit in these plus 2nd stadium females. Success of ovipositor insertion was unaffected by host stage. The outcome of these behaviors was preferential oviposition by E. diversicornis in the large female host stages. Acerophagus coccois Smith also preferentially examined larger female mealybugs (second and third stadium nymphs and adults) more than other stages and successfully inserted its ovipositor in these stages more often than in second stadium male nymphs and male cocoons, resulting in a similar preference in this species for larger female host stages. When given a choice between adult female hosts of two species, P. herreni and Phenacoccus gossypii Townsend & Cockerell, E. diversicornis exhibited a clear preference for P. herreni; whereas A. coccois preferred P. gossypii.

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Résumé Epidinocarsis diversicornis (Howard), ayant la possibilité de choisir entre six stades différents de Phenacoccus herreni Cox & Williams, examine avec ses antennes plus particulièrement les adultes et les larves femelles du 3ème stade, et essaie de pondre de préférence dans ces stades et les larves femelles de second stade. L'insertion de la tarière s'effectue aussi bien quel que soit le stade de l'hôte. Il résulte de ces différents aspects du comportement que E. diversicornis pond de préférence dans les femelles des stades les plus avancés. Acerophagus coccois Smith préfère aussi examiner les cochenilles femelles les plus grosses (second et 3ème stade larvaires et adulte), et introduit sa tarière avec succès dans ces stades plus souvent que dans les larves mâles de second stade ou les cocons mâles; il en résulte aussi pour cette espèce une préférence pour les femelles des stades les plus gros.Quand on leur a donné le choix entre des femelles des deux espèces de cochenilles (P. herreni et Phenacoccus gossypii Towsend & Cockerell), E. diversicornis manifestait une nette préférence pour P. herreni, tandis que A. coccois préférait P. gossypii.

     

Interactions between hosts and non-hosts of Pinus spp. and Matsucoccus josephi: anatomical responses of stem to infestation

Artificial infestation of seven pine species revealed that Matsucoccus josephi (Homoptera: Margarodidae) completes its development on Pinus brutia , P. eldarica and P. halepersis , whereas only a small number of the scale larvae infesting P. cunariensis and P. pined reached the second instar and none developed to the adult stage. M. josephi crawlers died while trying to feed on P. radiata and P. pinaster. Histological examination of the infested plant sections indicated that necrosis in shoot and stem barks of P. eldarica and P. halepensis occurs just before or after the scale completes its development. Injury reached the cambium, and traumatic resin ducts; parenchyma cells instead of tracheids and curved tracheids were formed. In P. brutia wound periderm was observed in the stem section but not in the shoot cortex following scale development. Wound periderm was also formed in the stem cortex of P. canariensis and P. pinena whereas no pathological changes were detected in the infested cortex of P. pinaster and P. radiata.
Mechanical lesions caused by needle punctures resulted in the production of parenchyma cells instead of tracheids in all four pine species investigated. The response of the pine cortex was non-specific; however several similarities in the response to scale infestation, such as the formation of resin ducts, were observed. We hypothesize that the response of the pine tissue to the scale saliva is a hypersensitive reaction. It is suggested that the development of Matsucoccus species on particular pine species is related to the scale's inability to trigger the defence system of the host while the larvae are feeding.