Amino acids and sugars in phloem sap of different parts of oats (Avena sativa) in relation to feeding sites of cereal aphids, Sitobion avenae and Metopolophium dirhodum (Hom., Aphididae) Pure phloem sap of different parts of oats (Avena sativa) was collected by cutting stylets of feeding aphids using a ruby laser. Aphids and plants were kept under constant environmental conditions. Only parts of oats preferred by the cereal aphids, Sitobion avenae and Metopolophium dirhodum were selected for the collection of phloem sap. Sucrose was the only sugar transported in the phloem. The concentration of sucrose was almost equal in the phloem sap of spikelet (254.4 μg/μl), flag leaf (252.4 μg/μl) and the leaf next to the flag leaf (293.9 μg/μl). The total concentration of amino acids ranged between 174.8 nmol/μl in the spikelet, 127.8 nmol/μl in the flag leaf and 121.1 nmol/μl in the leaf next to the flag leaf. Differences, however, were not significant. The proportion of amino acids to sucrose was 1:11 in the spikelet, 1:14 in the flag leaf and 1:18 in the leaf next to the flag leaf. Apart from the discrepancies in total concentrations qualitative and quantitative differences in single amino acids were found between the plant parts, especially between spikelets and leaves. A total of at least 32 amino acids were detected in the phloem sap. The dominating amino acids were glutamic acid, aspartic acid, glutamine, asparagine, threonine, serine, alanine and valine. In spikelets the content of glutamine, asparagine, valine, methionine, ornithine and two unknown amino acids (“unknown‐2” and “unknown‐4”) was significantly higher than that in the leaves, while the content of glutamic acid, aspartic acid, threonine, serine, glycine, ethanolamine and an unknown amino acid (“unknown‐1”) was significantly lower compared to the leaves. Differences between the spikelet and the leaf next to the flag leaf were in most cases higher than that between spikelet and flag leaf. Between the two leaves only the content of threonine and unknown amino acid “unknown‐1” was significantly different. Possible reasons for the preference of spikelets by S. avenae and flag leaves by M. dirhodum are discussed with reference to the composition of phloem sap. Zusammenfassung Unter konstanten Bedingungen wurden mit Hilfe einer Rubin‐Laser‐Apparatur inserierte Stechborsten von Getreideblattläusen Sitobion avenae durchtrennt und der austretende reine Phloemsaft verschiedener Pflanzenteile von Hafer (Avena sativa) gewonnen. Die Auswahl der Pflanzenorgane orientierte sich an der Saugortpräferenz von S. avenae und Metopolophium dirhodum. Saccharose war die einzige Transportform des Zuckers im Phloemsaft. Die Zuckerkonzentration im vorletzten Blatt war mit 293,9 μg/μl tendentiell höher als im Ährchen (254,4 μg/μl) oder Fahnenblatt (252,4 μg/μl). Bei der Gesamtkonzentration der Aminosäuren bestanden ebenfalls nur tendentielle Unterschiede zwischen den Pflanzenteilen (im Ährchen 174,8 nmol/μl, Fahnenblatt 127,8 nmol/μl und vorletzten Blatt 121,1 nmol/μl). D...

Factors influencing the efficiency of the aphidophagous gall midge, Aphidoletes aphidimyza (Rond.) (Diptera, Cecidomyiidae) Experiments on the efficiency of Aphidoletes aphidimyza (Rond.) were carried out in the laboratory at 21 °C and 75 % rel. humidity with its natural prey, the green peach aphid, Myzus persicae (Sulz.) reared either on brussel sprouts (Brassica oleracea var. gemmifera) or on artificial diet. When preying on 1–2 day‐old green peach aphids the total food consumption of the female larvae of A. aphidimyza was higher than that of the males. Larvae of both sexes, however, consumed about 50 % of their total food requirements in the last day—fourth day—of their development. Three‐day‐old larvae were inclined to pupate prematurely, if they were exposed to a period of starvation as short as only a few hours. The percentage of premature larvae inclined to pupate increased with extended period of starvation. Newly emerged females transfered reserve substances accumulated during larval development into egg production within the first two days of the adult life. The number of eggs thus produced was independent on the presence or absence of honeydew and males. The number of eggs produced did not change with increasing aging of the females, if they were supplied with only water. Adult midges of A. aphidimyza take in honeydew of the aphids, which is essential for the maintainance of their life. The life span of the males was, however, always shorter than that of the females. Also the total egg production of the females was significantly increased when honeydew was supplied. Under optimal nutritive conditions in both larvae and adult stage the honeydew intake of the famales made out 50–60 % of the total egg production, if the single females were kept together with only one male. Another 40–50 % could be realized through larval food without honeydew intake of the adults. These percentages varied, however, with the quality of the larval food and the proportion of ovipositing females. Insufficient feeding in the larvae stage due to starvation or less nutritiv quality of the supplied prey aphids (for instance, dead aphids killed with insecticides or through deep‐freezing) led to a reduction in egg production initially effected by larval reserve substances. Such a reduction could not be compensated through later intake of honeydew by adults. Mating is an absolute prerequisite for oviposition. This did not affect the number of eggs produced from the larval reserve substances in the first two days of adult life, if no honeydew was supplied. In the presence of honeydew, however, the weight of the females was significantly increased with a slight rise in egg production. During the whole adult life oviposition stimulated significantly the maturing of the eggs, and the total egg production was correspondingly increased significantly. The nutritive quality as well as the stimulating effect of honeydew on egg production, adult life span and oviposition was not significantly changed when fresh and 15 days'‐old honey...

Insect-transmitted plant pathogens can have positive, negative or no effects on the vector insect. Effects could be direct (caused by the pathogen) or indirect (mediated by changes in the plant). Pathogen effects on non-vector insects are less well known. Peregrinus maidis (Ashmead) (Homoptera: Delphacidae), an insect that is not a vector of the corn stunt spiroplasma (CSS), weighed less 15 days after feeding on CSS-infected corn plants relative to insects feeding on healthy corn plants. Fecundity of non-vector insects that were removed from diseased plants was higher than for insects coming from healthy plants. For Dalbulus maidis (DeLong & Wolcott) (Homoptera: Cicadellidae), an insect that transmits CSS, there were no differences in weight, longevity, eggs per day, weekly or total fecundity after feeding on healthy or on CSS-infected corn plants. Significant differences in some phloem amino acids were detected between healthy and CSS-infected plants. Infected plants also showed an increased phloem acidity as disease symptoms progressed. Feeding on CSS-infected corn plants by an insect that does not vector the pathogen infecting the plant can have favorable consequences as evidenced by an increased fecundity.

Cereal aphids as prey species for mass rearing of Aphidoletes aphidimyza (Rond.) (Dipt., Cecidomyiidae) in the biological control of Myzus persicae (Sulz.) in greenhouses Laboratory tests indicate that the cereal aphids Sitobion avenue, Metopolophium dirhodum and Rhopalosiphum padi possessed higher nutritive value for the larvae of Aphidoletes aphidimyza than the green peach aphid Myzus persicae. Adult weight and egg production from larval reserve substances were significantly increased. The duration of larval and pupal stage and the rate of adult emergence were the same between the aphid species.Results of greenhouse experiments using an open rearing unit of A. aphidimyza on cereal aphids show that the predatory midge could reproduce in and disperse from the open rearing unit to successfully control populations of peach aphids on sweet pepper. In the midge treated greenhouses the aphid population densities remained at very low levels throughout the entire vegetation period. In the midge free greenhouses, however, population growth of the aphid increased very rapidly reaching peak population densities 4-5 weeks after aphid infestation. In two of the experiments midges were accidentally introduced into the midge free greenhouse. It became evident that the midge were able to suppress aphid populations effectively, even if the aphid density had reached a relatively high level.Cereal aphids are suggested as prey species for mass rearing of A . aphidimyza. The effectiveness of A . aphidzmyza in suppressing aphid populations and the advantages of using open rearing unit in form of a "cereal aphids -A. aphidzmyza"system for control greenhouse aphids are discussed.