Orientation and ingestion rates of larval Anopheles albimanus in response to floating particles

Response of fourth-instar larvae of Anopheles albimanus Wiedemann (Diptera: Culicidae) to food and inert particles floating at the water surface was studied. In a choice test, larvae aggregated at powdered organic materials (blood meal, liver powder alfalfa flour and wheat flour) but not at inert materials (kaolin, chalk or charcoal). Larvae responded positively to proteins as well as some carbohydrates, but not to cellulose. Retention of larvae at food sources found by random locomotion was found to be responsible for larval aggregation. Larvae ingested food particles 6–9 times faster than insert particles. The significance of Anopheline feeding behavior in the development of formulations of stomach toxins (bacterial agents) used in larval control is discussed.

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Zusammenfassung Die vorliegende Studie befasst sich mit Verhaltensreaktionen von Anopheles albimanus Viertlarven auf an der Wasseroberfläche schwimmende Partikel. Verteilung und Orientierung der Larven wurde in einer Wahlapparatur quantifiziert. Nach Auftrag von Alfalfamehl, Weizenmehl, Stärke, Blutmehl, Leberpulver und Fischmehl wurde Aggregation der Larven in den beköderten Fächern der Apparatur beobachtet. Sowohl Proteine (Casein) als auch einige Kohlehydrate (Amylose, Amylopectin) lösten Aggregationen der Larven aus. Im Unterschied dazu führte Auftrag von Kreide, Kaolin, Polyaethylenpulver, Talcum oder Cellulose nicht zu Aggregationen. Zur Beschreibung der Entstehung larvaler Aggregationen bei Futterstoffen wurden die Schwimmbewegungen der Larven in Anwesenheit von Weizenmehl als Ködersubstanz quantifiziert. Da keine Attraktion der Larven im Sinne einer gerichteten Schwimmbewegung beobachtet werden konnte, wird geschlussfolgert, dass sofortige Beendung der Suchaktivität der Larven bei zufällig gefundenen Futterquellen für die beobachteten Aggregationen bei organischen Substanzen verantwortlich ist.Die Fressraten der Larven bei Angebot verschiedener Substanzen im Überschuss wurde bestimmt. Larven fülten drei von insgesamt sechs Darmabschnitten innerhalb von 15–30 min bei Angebot von Futtersubstanzen, während die Füllung von nur zwei Darmabschnitten mit inerten Materialien erst nach 90–120 min zu beobachten war. Die Resultate werden in Bezug auf wasseroberflächengebundene Formulierungen von Frassgiften diskutiert. Inerte Trägersubstanzen werden wahrscheinlich wesentlich langsamer aufgenommen als Futtersubstanzen. Da An. albimanus Larven nicht von Futterquellen angezogen werden, ist eine rasche und wirksame Giftaufnahme besonders dann zu erwarten, wenn die gesamte Oberfläche der Brutgewässer mit toxinhaltigen Trägerpartikeln bedeckt werden kann.

     

Gender identification of shovelnose sturgeon using ultrasonic and endoscopic imagery and the application of the method to the pallid sturgeon

Monthly sampling of shovelnose sturgeon Scaphirhynchus platorynchus , a biological surrogate for the endangered pallid sturgeon Scaphirhynchus albus , was conducted to develop a multi‐seasonal profile of reproductive stages. Data collected included histological characteristics of gonads from wild caught fish and laboratory and field ultrasonic and endoscopic images. These data were used to compare effectiveness of ultrasonic and endoscopic techniques at identifying gender of adult shovelnose sturgeon at different reproductive stages. The least invasive method ( i.e . ultrasound) was least effective while the most invasive ( i.e . endoscope through an abdominal incision) was the most effective at identifying shovelnose sturgeon gender. In most cases, success rate for identifying males was greater than females, with success at identifying both genders greater in more advanced reproductive stages. Concomitantly, for most months average reproductive stage was more advanced for males than females. April and May were the months with the most advanced reproductive stage, and were the months when ultrasound was most effective. Methods were also applied in the Upper Missouri River to validate their use on pallid sturgeon Scaphirhynchus albus . Ultrasound was successful at identifying pallid sturgeon gender, however, endoscopic examination through the urogenital duct was only successful at identifying pallid sturgeon gender when the urogenital duct was not opaque.     

Maternal induction of larval diapause and its sensitive stage in the blow fly Lucilia sericata (Meigen) (Diptera: Calliphoridae)

Lucilia sericata has a facultative diapause in the third larval instar after cessation of feeding. Induction of the diapause is influenced by the photoperiod and temperature conditions experienced by insects in the parental generation as well as those experienced by the larvae themselves. The sensitive stage of the parental generation for induction of diapause was examined using diapause‐averting conditions of 16 h light : 8 h darkness (LD 16:8) at 25°C and diapause‐inducing conditions of LD 12:12 at 20°C. The incidence of diapause in the progeny was predominantly determined by the conditions experienced by the parents in the adult stage. Moreover, the results of reciprocal crosses showed that only the mother's experience is involved in the induction of diapause in the progeny.     

A Survey Investigating the Infection of Fusarium langsethiae and Production of HT‐2 and T‐2 Mycotoxins in UK Oat Fields

Fusarium langsethiae is a toxigenic fungal species that has been reported in European small‐grain cereal crops such as oats, wheat and barley. Although its relative contribution to fusarium head blight (FHB) symptoms is not well understood, it is reported to contaminate these cereals with high levels of HT‐2 and T‐2 trichothecenes mycotoxins that are currently under consideration for legislation by the European Commission. Ten commercial oat fields in Shropshire and Staffordshire (two adjacent counties in the Midlands) in the UK were surveyed in the 2006/2007 growing season. Samples were taken from predetermined field locations at Zadoks growth stages 32/33, 69, 77‐85 and 90‐92 for F. langsethiae biomass and HT‐2 and T‐2 toxins quantification. The results from this study showed that oats can be heavily infected with F. langsethiae and have high concentrations of HT‐2 and T‐2 toxins with no apparent FHB symptoms. The regression of HT‐2 + T‐2 toxins on F. langsethiae DNA concentration was highly significant (P < 0.001, r² = 0.55). The results indicated that although F. langsethiae had no direct effect on crop yield, it may result in indirect economic losses where the grain can be rejected or downgraded as a result of intolerable levels of HT‐2 and T‐2 toxins, which are of human food and animal feed safety concern. The influence of cultural field practices on the infection and HT‐2 and T‐2 toxins accumulation in oats was not clear and warrants further studies to identify the sources of F. langsethiae inoculum and conditions favourable for infection and mycotoxin production.     

Analysis of nuclear proteins from silk glands ofBombyx mori

A gentle method for the isolation of nuclei from developing silk glands ofBombyx mori has been standardized. The nuclei, whether isolated or directly visualizedin situ within the silk glands, exhibit complex morphology. The nuclei occupy almost the entire volume of the gigantic silk gland cells. Although the isolated nuclei still retain their ramified morphology, being polyploid they are fragile and often become fragmented. The histone and low-salt-extractable proteins from nuclei isolated from the middle and posterior silk glands on different days of the fourth and fifth instars of larval development have been analysed. The histones did not show any stage- or tissue-specific variations whereas the low-salt-extractable proteins showed some developmental stage specific variation. Using the antibody raised against one such protein, its absence in the early stage of development has been confirmed by Western blotting techniques. This developmental stage specific protein may be functionally linked to some activities responsible for boosting up the production of silk or silk-related proteins during the fifth instar of larval development.     

蓖麻蚕前胸腺细胞超微结构的变化与蜕皮激素分泌活动的关系

本研究叙述蓖麻蚕Philosamia cythia ricini四龄及五龄幼虫前胸腺蜕皮激素分泌活动各不同时期所显示的腺细胞超微结构变化.从幼虫蜕皮后至进入眠期之间的腺细胞结构可分为三个时期,(1)不活动期:细胞核呈圆形,核内密布染色质及核仁,细胞质内有结构完整的线粒体、粗面及滑面内质网、核糖体和高尔基氏体;细胞外围的细胞间区内有许多小囊泡及多泡囊.(2)活动期:细胞结构变化为细胞核膜出现内陷、外突,形成波浪形的核周膜;线粒体变形,出现内嵴稀疏的空心线粒体.(3)激素释放期:细胞核变形,形成若干长短不一向外伸出的指状突,有些伸达细胞边缘;其余细胞器退化,其后仅余残缺的高尔基氏体,稀疏的核糖体,线粒体的内崤逐渐消失,成为空腔扩大的及空腔内藏“膜轮”的线粒体,和一些溶解体及大形“膜轮”.     

Filtration rates of mosquito larvae in suspensions of latex microspheres and yeast cells

Filtration rates of fourth instars of Aedes aegypti L., Anopheles albimanus Wiedemann, Anopheles quadrimaculatus Say and Culex quinquefasciatus Say (Diptera: Culicidae) were determined by quantifying removal rates of suspended latex microspheres or yeast cells. Average filtration rates were 33–34 l/larva/h (An. quadrimaculatus), 49–55 (An. albimanus), 490–590 (C. quinquefasciatus) or 590–690 l/larva/h (Ae. aegypti) for larvae exposed to latex beads suspended in phagostimulant yeast extract solutions. In suspensions of yeast cells, filtration rates of Ae. aegypti and C. quinquefasciatus were not significantly different from filtration rates in latex bead suspensions. Larval density, ranging from 0.3 to 2.4 individuals/ml in tests with Ae. aegypti and C. quinquefasciatus and up to 4.8 larvae/ml in tests with Anopheles, did not influence filtration rates.

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Zusammenfassung Die Filtrierraten von Viertlarven der Stechmückenarten Aedes aegypti, Anopheles albimanus, Anopheles quadrimaculatus und Culex quinquefasciatus wurden in Laborversuchen bestimmt. Dabei wurde die Filtrierrate definiert als ein Wasservolumen, welches pro Stunde von einer Larve von den Testpartikeln (Hefezellen oder Latexkugeln mit einem Durchmesser von 2 m) befreit wurde. Nach Exposition der Larven in Dichten zwischen 0.15 und 2.4 Larven/ml (Ae. aegypti und C. quinquefasciatus), oder zwischen 0.6 und 4.8 Larven/ml (Anopheles) wurde der Partikelgehalt der Suspensionen in einem elektronischen Partikelzähler bestimmt. Die Filtrierraten wurden über die Verringerung der Partikeldichte mit zunehmender Larvendichte entsprechend einer in der Literatur angegebenen Formel berechnet.Suspensionen von Hefezellen wurden von Ae. aegypti Larven mit einer Leistung von 680±220 l/Larve/h gefiltert. Bei Larven von C. quinquefasciatus wurden Filtrierraten von 600±120 l/Larve/h gemessen. Die Filtrierraten beider Arten waren unabhängig von der Larvendichte. In Suspensionen von Latexpartikeln (zur Phagostimulation der Larven wurden diese Partikel in Lösungen von Hefeextrakt angeboten) wurden die folgenden Filtrierraten festgestellt: An quadrimaculatus: 33–34, An. albimanus: 49–55, C. quinquefasciatus: 490–590, und Ae. aegypti: 560–690 l/Larve/h. Die Larvendichte hatte auch hier keinen Einfluss auf die Filtrierrate. Hefezellen und Latexpartikel wurden von Ae. aegypti und C. quinquefasciatus mit statistisch nicht signifikant verschiedenen Filtrierraten aufgenommen. Die Filtrierraten der Anopheles Larven waren um mehr als eine Zehnerpotenz kleiner als die Filtrierraten von Culex und Aedes, und auch untereinander signifikant verschieden. Der Einfluss der Filtrierraktivität von Stechmückenlarven auf das Seston der Brutgewässer wird diskutiert.

     

Prediction of a low dose herbicide effect from studies on binding of metribuzin to the chloroplasts of Chenopodium album L.

Chenopodium album L. seedlings at the 4- and 8-leaf stage were exposed to low concentrations metribuzin [4-amino-6-(l, l-dimethyl)-3-(methylthio)-l,2,4-triazin (4 H )-one] in nutrient solution to study herbicide uptake and the effects of low-dose rates. Chlorophyll fluorescence was measured to relate the inhibition of photosynthesis to herbicide dose. The minimum rate at which metribuzin fully inhibited photosynthesis was less than 1 μM for seedlings at the 4-leaf stage of development, and between 1 and 5 μM for the 8-leaf stage seedlings. With isolated chloroplasts, experiments were conducted to establish the relationship between the amount of herbicide molecules bound to each chloroplast and the inhibition of photosynthesis. From the dose-response curves obtained it was calculated that photosynthesis was fully inhibited when 7.5 10⁵ molecules metribuzin were bound to each chloroplast. This amount of binding was used to estimate minimum-lethal dose rates of metribuzin required for seedlings differing in fresh weight of leaves and amounts of chloroplasts present. It is suggested that prediction of a low dose herbicide effect from studies on binding of photosystem-II inhibitors in combination with chlorophyll fluorescence measurements may lead to the development of a new weed management strategy.     

Sex ratio regulation in the waspEupelmus vuilleti (crwf.), an ectoparasitoid on bean weevil larvae (Hymenoptera: Pteromalidae)

In Africa, the seeds and/or pods ofVigna unguiculata andVigna radiata (Papilionacea) are attacked in fields and storage structures by bruchid beetlesCallosobruchus maculatus andBruchidius atrolineatus, on which parasitoid communities can develop. One of these parasitoids is the solitary ectoparasitoidEupelmus vuilleti (Eupelmidae). The storage conditions ofV. unguiculata andV. radiata favor the overlapping of all host stages during several months. These conditions suggest that female parasitoids would vary the sex ratio of their offspring according to the different sizes or developmental stages of hosts. The sex ratio ofE. vuilleti was strongly related to the developmental stage of the hostC. maculatus. Under our experimental conditions, where superparasitism is rare, the proportion of daughters varied between 5 and 25% on the third larval stage but reached 70 to 90% on the pupae. The increase in the proportion of daughters was also observed in the absence of superparasitism. In this case, there was an absolute coincidence between the sex ratio of eggs laid and that of emerged adults. Manipulation of the sex of the egg by the females seems to take place at the time of the egg's fertilization. The relation between host weight and egg sex showed that the male eggs are preferentially laid on lighter host larvae and the female eggs on heavier ones.