Search

Chapter 1: the environmental conditions in greenhouses differ in many respects from those in the open field. Both the climate and the crops are different. A free exchange between the fauna of the greenhouses and the open air is hampered by the glass walls and roofs. The isolating effect of greenhouses on arthropod pests contributes to the effectiveness of control measures, but also to the development and maintenance of pesticide resistance in greenhouses. Because of the special conditions a specific fauna exists in greenhouses, and the use of exotic predators and parasites for biological control is possible. The greenhouse environment acts as a "sieve" only allowing such species to thrive that are adapted to these special conditions. These are sometimes exotic species that cannot thrive in the open in the Dutch climate. Native species may penetrate into greenhouse cultures, but to pass the "sieve" they have to adapt to greenhouse conditions.The leaf-roller Clepsis spectrana Tr. is native in the Netherlands. It gives an example of the development of a greenhouse-adapted biotype. In Dutch greenhouses, especially on roses, it causes much damage. In heated greenhouses, where artificial illumination is not given, growth and reproduction of C. spectrana continue without diapause during winter, which is advantageous for the species in this environment, where the difference between summer and winter temperatures does not exceed a few degrees and suitable food is available all the year round.Chapter 2 deals with the morphology, bionomics, host plant range, and distribution area of C. spectrana. Chapter 3 describes the materials and methods.Chapter 4: the number of larval instars from egg hatching to pupation varied between 4 and 8 in both field and greenhouse strains. Each larval growth type had its own specific progression of head capsule width. The difference in head capsule width between the 4- and 5-instar type was already evident in the 1st instar, between the Sand 6-instar type in the 2nd instar, and between the 6- and 7-instar type only in the 3rd instar or even later. Females tended to develop through a higher number of instars than males, but 5 instars was the most usual in both sexes. The development duration was the same in field and greenhouse strains, in each of the immature stages. The upper thermal limit for development was between 30 °C and 35 °C in both field and greenhouse strains, whereas the developmental threshold was close to 10 °C. An adaptation of greenhouse populations of C. spectrana to development at higher temperatures did not appear.Chapter 5: short daylength induced diapause in field strains in the larval stage. The critical photoperiod was between 16 and 17 hours. The number of moults up to the onset of diapause varied between 2 and 6, and was determined by the photoperiod. Larvae from eggs hatching later in the season entered diapause after a lower number of moults. The time of resumption of growth after diapause termination in spring was not correlated with the date of egg hatching in the previous year, in outdoor experiments. The larvae underwent supernumerary moults after termination of diapause. The duration of post-diapause development was longer as diapause had been entered after less moults. The number of moults after termination of diapause, and the duration of post-diapause development, were sex-linked. The functional significance of these phenomena is discussed.Chapter 6: the photoperiodic response of 5 different greenhouse strains, originating from larvae and pupae collected in different rose houses at different times of the year (both in summer and in winter), was tested in the laboratory. These greenhouse strains did not enter diapause, at both 20 °C and 15 °C, regardless of the photoperiod, One greenhouse strain was also reared outdoors. Egg hatching dates were August 1, August 17, September 25, and October 14. At least the major part of the larvae did not enter diapause.Chapter 7: field strain larvae entered diapause in a heated greenhouse, but the absence of a period of chilling caused an abnormal growth pattern in these larvae, compared to larvae terminating their diapause outdoors: (a) larval development duration was extremely variable (larvae from field strain eggs that hatched at August 24 in the greenhouse, pupated between January 28 and July 15 of the following year), (b) The difference in mean developmental time between male and female larvae was greatly increased, and (c) the mean number of moults, and the variation in the number of moults, Were increased. The survival of diapausing larvae, however, was not essentially affected by the absence of a period of chilling. The time required for diapausing larvae to reach the pupal stage under conditions without a cold period, was genetically determined, and could be shortened rapidly by selection.Chapter 8: a difference in the composition of the female sex pheromone between field and greenhouse strains could not be shown, nor in the calling behaviour of virgin females in relation to the light-dark cycle. Release-recapture trials revealed that females of both strains attracted males of both strains in equal proportions. There did not appear to be a difference in mating preference.Chapter 9: the index of genetic identity (I) of a field population on stinging nettles from the middle of the country, and a rose house population from the West of the country, amounted to 0.994 (based on allozyme frequencies). This is the level for panmictic populations of one species. Field and greenhouse strains could readily be intercrossed, with a viable F2 generation.Chapter 10: field and greenhouse populations of C. spectrana are certainly still conspecific. It is adequate to speak of a "field biotype" and a "greenhouse biotype". The greenhouse biotype is characterised by absence of the ability to enter diapause. When the biotypes are brought together, hybridization and introgression certainly will occur. Immigration of the field biotype into heated greenhouses apparently is sufficiently low to maintain a separate greenhouse biotype with constant characteristics. The origin of the greenhouse biotype might be a non-diapausing geographic race of C. Spectrana, from the warmest parts of its distribution area, or the field biotype immigrated into heated greenhouses, and subsequently lost its ability to enter diapause. The last possibility seems the most likely.Chapter 11: pheromonal trapping of C. spectrana is less effective in greenhouses than in the open air. Probably the specific nature of the air movements in greenhouses reduces the effectiveness of the long- range pheromone-mediated behaviour of the males. However, male pheromone-mediated behaviour in short-range orientation, close to calling females, may be unaffected (chapter 8.3). This decreases the effect of synthetic pheromone used for monitoring and mass trapping. However, application of the communication disruption technique may be successful under glass, because the overall concentration of synthetic pheromone in the air can be made much higher in greenhouses than in the open field. Further research is recommended.Controlling C. spectrana in greenhouses by releasing sterile males seems feasible, as: (a) immigration of new adults from outside almost certainly is negligible, and (b) C.spectrana is the only tortricid occurring in the Dutch floriculture; the danger that other leaf-rollers will take over when chemical control of C. spectrana ceases seems therefore small.Diapause can be crossed into greenhouse populations of C. spectrana by releasing males of the field biotype. This probably is an ineffective way of controlling these populations.Parasitised C. spectrana larvae were found in several greenhouses, even in winter. The parasites, which were not identified, apparently were not diapausing. It is recommended to make a survey of the parasite fauna of C. spectrana in greenhouse cultures. Beschrijving van het aan de omstandigheden van Nederlandse kassen aangepaste biotype van de bladroller (Clepsis spectrana) wat betreft morfologie, fenologie, reactie op daglengte, samenstelling van geslachtsferomonen en kruisbaarheid met veldpopulaties

Chapter 1: the environmental conditions in greenhouses differ in many respects from those in the open field. Both the climate and the crops are different. A free exchange between the fauna of the greenhouses and the open air is hampered by the glass walls and roofs. The isolating effect of greenhouses on arthropod pests contributes to the effectiveness of control measures, but also to the development and maintenance of pesticide resistance in greenhouses. Because of the special conditions a specific fauna exists in greenhouses, and the use of exotic predators and parasites for biological control is possible. The greenhouse environment acts as a "sieve" only allowing such species to thrive that are adapted to these special conditions. These are sometimes exotic species that cannot thrive in the open in the Dutch climate. Native species may penetrate into greenhouse cultures, but to pass the "sieve" they have to adapt to greenhouse conditions.The leaf-roller Clepsis spectrana Tr. is native in the Netherlands. It gives an example of the development of a greenhouse-adapted biotype. In Dutch greenhouses, especially on roses, it causes much damage. In heated greenhouses, where artificial illumination is not given, growth and reproduction of C. spectrana continue without diapause during winter, which is advantageous for the species in this environment, where the difference between summer and winter temperatures does not exceed a few degrees and suitable food is available all the year round.Chapter 2 deals with the morphology, bionomics, host plant range, and distribution area of C. spectrana. Chapter 3 describes the materials and methods.Chapter 4: the number of larval instars from egg hatching to pupation varied between 4 and 8 in both field and greenhouse strains. Each larval growth type had its own specific progression of head capsule width. The difference in head capsule width between the 4- and 5-instar type was already evident in the 1st instar, between the Sand 6-instar type in the 2nd instar, and between the 6- and 7-instar type only in the 3rd instar or even later. Females tended to develop through a higher number of instars than males, but 5 instars was the most usual in both sexes. The development duration was the same in field and greenhouse strains, in each of the immature stages. The upper thermal limit for development was between 30 °C and 35 °C in both field and greenhouse strains, whereas the developmental threshold was close to 10 °C. An adaptation of greenhouse populations of C. spectrana to development at higher temperatures did not appear.Chapter 5: short daylength induced diapause in field strains in the larval stage. The critical photoperiod was between 16 and 17 hours. The number of moults up to the onset of diapause varied between 2 and 6, and was determined by the photoperiod. Larvae from eggs hatching later in the season entered diapause after a lower number of moults. The time of resumption of growth after diapause termination in spring was not correlated with the date of egg hatching in the previous year, in outdoor experiments. The larvae underwent supernumerary moults after termination of diapause. The duration of post-diapause development was longer as diapause had been entered after less moults. The number of moults after termination of diapause, and the duration of post-diapause development, were sex-linked. The functional significance of these phenomena is discussed.Chapter 6: the photoperiodic response of 5 different greenhouse strains, originating from larvae and pupae collected in different rose houses at different times of the year (both in summer and in winter), was tested in the laboratory. These greenhouse strains did not enter diapause, at both 20 °C and 15 °C, regardless of the photoperiod, One greenhouse strain was also reared outdoors. Egg hatching dates were August 1, August 17, September 25, and October 14. At least the major part of the larvae did not enter diapause.Chapter 7: field strain larvae entered diapause in a heated greenhouse, but the absence of a period of chilling caused an abnormal growth pattern in these larvae, compared to larvae terminating their diapause outdoors: (a) larval development duration was extremely variable (larvae from field strain eggs that hatched at August 24 in the greenhouse, pupated between January 28 and July 15 of the following year), (b) The difference in mean developmental time between male and female larvae was greatly increased, and (c) the mean number of moults, and the variation in the number of moults, Were increased. The survival of diapausing larvae, however, was not essentially affected by the absence of a period of chilling. The time required for diapausing larvae to reach the pupal stage under conditions without a cold period, was genetically determined, and could be shortened rapidly by selection.Chapter 8: a difference in the composition of the female sex pheromone between field and greenhouse strains could not be shown, nor in the calling behaviour of virgin females in relation to the light-dark cycle. Release-recapture trials revealed that females of both strains attracted males of both strains in equal proportions. There did not appear to be a difference in mating preference.Chapter 9: the index of genetic identity (I) of a field population on stinging nettles from the middle of the country, and a rose house population from the West of the country, amounted to 0.994 (based on allozyme frequencies). This is the level for panmictic populations of one species. Field and greenhouse strains could readily be intercrossed, with a viable F2 generation.Chapter 10: field and greenhouse populations of C. spectrana are certainly still conspecific. It is adequate to speak of a "field biotype" and a "greenhouse biotype". The greenhouse biotype is characterised by absence of the ability to enter diapause. When the biotypes are brought together, hybridization and introgression certainly will occur. Immigration of the field biotype into heated greenhouses apparently is sufficiently low to maintain a separate greenhouse biotype with constant characteristics. The origin of the greenhouse biotype might be a non-diapausing geographic race of C. Spectrana, from the warmest parts of its distribution area, or the field biotype immigrated into heated greenhouses, and subsequently lost its ability to enter diapause. The last possibility seems the most likely.Chapter 11: pheromonal trapping of C. spectrana is less effective in greenhouses than in the open air. Probably the specific nature of the air movements in greenhouses reduces the effectiveness of the long- range pheromone-mediated behaviour of the males. However, male pheromone-mediated behaviour in short-range orientation, close to calling females, may be unaffected (chapter 8.3). This decreases the effect of synthetic pheromone used for monitoring and mass trapping. However, application of the communication disruption technique may be successful under glass, because the overall concentration of synthetic pheromone in the air can be made much higher in greenhouses than in the open field. Further research is recommended.Controlling C. spectrana in greenhouses by releasing sterile males seems feasible, as: (a) immigration of new adults from outside almost certainly is negligible, and (b) C.spectrana is the only tortricid occurring in the Dutch floriculture; the danger that other leaf-rollers will take over when chemical control of C. spectrana ceases seems therefore small.Diapause can be crossed into greenhouse populations of C. spectrana by releasing males of the field biotype. This probably is an ineffective way of controlling these populations.Parasitised C. spectrana larvae were found in several greenhouses, even in winter. The parasites, which were not identified, apparently were not diapausing. It is recommended to make a survey of the parasite fauna of C. spectrana in greenhouse cultures.

African range cattle respond well to intensive feeding in feedlots, when maize silage based rations are fed. Maize is not drought-tolerant and is lodging-susceptible, which makes it less attractive as a forage. In a search for alternative forages, a new group of plant material is introduced: high-altitude, cold-tolerant sorghum. Some of the cultivars in this group appear to outyield maize both in terms of total dry matter and grain yield, over a large range of environmental conditions in the Kenyan highlands. Crop husbandry trials with the new sorghums and maize are reported. In an animal feeding trial the cattle performance of maize and sorghum silage based rations is compared. The introduction of new high-altitude, cold-tolerant grain type sorghums may eventually lead to a substantial increase of the area under arable agriculture in Kenya, because it will make grain production feasible in areas which were previously considered too dry for reliable grain production. A discussion of the typical problems of working on agricultural development in a developing country is given.

Bespreking van opgenomen soorten in de Wageningse demonstratie/variabiliteitstuin, die door het Centrum voor Genetische bronnen Nederland in samenwerking met de Stichting voor Plantenveredeling is opgezet. Behalve achtergrondinformatie over de soorten (o.a. oorsprong, variabiliteit, inhoudstoffen en opbrengst) wordt een indicatie gegeven van de te verwachten knelpunten op veredelings- en teelttechnisch gebied en een globale inschatting van de potentie van de verschillende soorten. Aan de orde komen: 11 oliehoudende gewassen, 7 eiwit- of zetmeelgewassen, 2 vezelgewassen, 3 farmacologische gewassen en tenslotte aardpeer

African range cattle respond well to intensive feeding in feedlots, when maize silage based rations are fed. Maize is not drought-tolerant and is lodging-susceptible, which makes it less attractive as a forage. In a search for alternative forages, a new group of plant material is introduced: high-altitude, cold-tolerant sorghum. Some of the cultivars in this group appear to outyield maize both in terms of total dry matter and grain yield, over a large range of environmental conditions in the Kenyan highlands. Crop husbandry trials with the new sorghums and maize are reported. In an animal feeding trial the cattle performance of maize and sorghum silage based rations is compared. The introduction of new high-altitude, cold-tolerant grain type sorghums may eventually lead to a substantial increase of the area under arable agriculture in Kenya, because it will make grain production feasible in areas which were previously considered too dry for reliable grain production. A discussion of the typical problems of working on agricultural development in a developing country is given.

Bespreking van opgenomen soorten in de Wageningse demonstratie/variabiliteitstuin, die door het Centrum voor Genetische bronnen Nederland in samenwerking met de Stichting voor Plantenveredeling is opgezet. Behalve achtergrondinformatie over de soorten (o.a. oorsprong, variabiliteit, inhoudstoffen en opbrengst) wordt een indicatie gegeven van de te verwachten knelpunten op veredelings- en teelttechnisch gebied en een globale inschatting van de potentie van de verschillende soorten. Aan de orde komen: 11 oliehoudende gewassen, 7 eiwit- of zetmeelgewassen, 2 vezelgewassen, 3 farmacologische gewassen en tenslotte aardpeer

Paintings produced in Flanders and Holland from the 16th to the 19th centuries are useful sources for a study of the evolution of domesticated crops. They show many types of vegetables, fruits, and ornamentals that are either not described or scantly mentioned in the literature of that period. So we come across "really red" cabbage, which may have been called roosken, and cauliflower with stems some 25 cm long. We further notice many colour variants of grapes, study of which may well provide information on the variation present in the crop at the time. Spikes of wheat and barley were rarely depicted. The few spikes of wheat shown resemble the variety Zeeuwse Witte, a landrace replaced around 1900. Many paintings and illustrations by Flemish and Dutch artists have been distributed all over the world. These works can therefore be investigated in many places for information on the history of domesticated crops. Schilderstukken met afbeeldingen van groenten, vruchten en sierplanten afkomstig van Vlaamse en Nederlandse kunstenaars uit de 16e tot 19e eeuw zijn over de gehele wereld verspreid. Ze kunnen daardoor op vele plaatsen onderzocht worden op gegevens over de geschiedenis of evolutie van deze gewassen waarover weinig literatuur over de betreffende periode bestaat. Zo vindt men bijvoorbeeld echte rode kool roosken genaamd en bloemkool met strengels van 25 cm lang. De wilde aardbei komt veel voor door de ze symbolische betekenis in de christelijke godsdienst. Ook druiven zijn vaak geschilderd en in vele kleurvarianten doordat ze symbolisch zijn voor vruchtbaarheid. Als siergewas is de tulp genoemd die voornamelijk in Nederland voorkwam

Vegetatie onkruid akkerbouw Stiboka onderzoek