Optimum prediction of three-way crosses from single crosses in forage maize (Zea mays L.)

Summary Three-way cross means were predicted with formulae involving linear functions of general (GCA) and specific combining ability (SCA) effects estimated from single-cross factorials between genetically divergent populations. Data from an experiment with 66 single-cross and 66 three-way cross forage maize (Zea mays L.) hybrids was used for comparing the prediction formulae. The genotypic correlation (r) between observed and predicted three-way crosses increased with increasing , the weighting factor of SCA effects, for plant height and ear dry matter (DM) content. It displayed slightly convex curves for total and stover DM yield, ear percentage, and metabolizable energy content of stover. For Jenkins' method B, r was considerably less than 1.0 for all traits, indicating the presence of epistasis. The square root of heritability (h) of the predicted means decreased with increasing , the reduction being small with a greater number of test environments. Using the product r·h as a criterion of efficiency, none of the prediction methods was consistently superior and the differences among them were rather small (< 7.5%) for all traits, irrespective of the number of test environments. We recommend evaluating the GCA of a greater number of lines from each parent population in testcrosses with a small number of elite lines from the opposite population. All possible three-way or double crosses between both sets of lines should be predicted by Jenkins's method C. This procedure allows one to select with a higher intensity among the predicted hybrids and thus should increase the genetic gain.Extended version of a paper (Geiger et al. 1986) read at the sixth meeting of the EUCARPIA Section Biometrics in Plant Breeding held at Birmingham, UK, July 28–August 1, 1986     

Competition-induced switch in young of the year perch,Perca fluviatilis: an experimental test of resource limitation

Synopis Reproductively developed male fathead minnows, Pimephales promelas, exhibited courtship behaviour in the presence of female conspecifies under laboratory conditions. Male courtship consisted of several distinctive and visually conspicuous behaviours directed toward females, including approach, display, and two contact behaviours, as well as leading behaviour from the female to a suitable spawning site. An ovulated condition in females was not necessary to generate male courtship behaviour; in fact, the amount of courtship exhibited by males may depend inversely on the readiness of females to spawn.     

Effects of propoxur exposure on females of the German cockroach, Blattela germanica and their oothecae

Susceptible and insecticide resistant females of Blattella germanica (L.), Dictyoptera, were exposed to propoxur treated surfaces. They carried oothecae that were expected to hatch in 48 to 72 h. Hatch was delayed in females that retained their oothecae throughout the exposure period. Oothecal hatch and nymphal survival were reduced when oothecae hatched on a treated surface but not when oothecae were retained and hatched on an insecticide-free surface. Over half of the susceptible strain females dropped their oothecae during the exposure period while very few resistance females dropped oothecae prematurely. Mortality of susceptible females that dropped their oothecae was higher than among those that retained oothacea. A tendency in this direction was apparent among the few resistant females that dropped their oothecae. The number of nymphs that emerged on the treated surface and also that survived for 24 h was higher in the resistant than in the susceptible strain. Newly hatched nymphs were frequently attached to the oothecae due to an inability to shed the embryonic cuticle.

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Résumé Des femelles de B. germanica, sensibles ou résistantes aux insecticides, ont été mises en présence de surfaces traitées au propoxure. Elles portaient des oothèques dont l'éclosion était attendue entre 48 et 72 h plus tard. Les éclosions ont été retardées, les femelles ayant conservé leurs oothèques pendant toute la période d'exposition. Lex taux d'éclosion des oothèques et de survie larvaire ont été normaux quand il y a eu rétention de l'oothèque et émission sur une surface saine, par contre ils étaient réduits quand l'oothèque a été émise sur une surface traitée. Plus de la moitié des femelles de la souche sensible ont laché leur oothèque pendant la période d'exposition tandis que très peu de femelles de la souche résistante ont abandonné leur oothèque prématurément. La mortalité était plus élevée chez les femelles sensibles qui ont perdu leur oothèque que chez celles qui l'avaient conservée. Une tendance du même type était décelable parmi les quelques femelles de la souche résistante qui perdirent leur oothèque. Le nombre d'écolosions de larves et le nombre de survies larvaires à 24 h étaient plus élevés dans la souche résistante que dans la souche sensible. Les larves néonates étaient souvent fixées à l'oothèque par suite de leur incapacité à se dépouiller de la cuticle embryonnaire.

     

Variation in feeding behaviour of Nilaparvata lugens on resistant and susceptible rice varieties

The feeding behaviour of Nilaparavata lugens was monitored on three rice varieties showing different levels of resistance in the Philippines, using a video-assisted observation method. N. lugens made more frequent, shorter probes on the moderately resistant IR46 and resistant IR62 rice varieties than on the susceptible IR22. Honeydew production was significantly lower on the resistant varieties though insect weight gains in 24 h were similar on IR46 and IR22, both being significantly greater than on the highly resistant variety.Population development, growth index and damage ratings were low on IR62 indicating antibiosis and/or non preference. When IR46 plants were infested as seedlings population increase, growth index and damage ratings were similar to those on the susceptible IR22. When infested at a later stage of plant growth the damage rating showed a moderate level of resistance though some population development was maintained, indicating antibiosis and tolerance. N. lugens started probing less frequently after surface exploration on both resistant varieties than on IR22 suggesting the presence of a resistance factor associated with the surface waxes of these varieties.

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Résumé Le comportement alimentaire de Nilaparvata lugens sur variétés de riz, sensible (IR22), partiellement résistante (IR46) et fortement résistante (IR62), a été contrôlé avec une méthode associant la vidéo à l'observation. N. lugens faisait des piqûres plus fréquentes et plus brèves sur IR46 et IR62, que sur la variété sensible. La production de miellat était significativement plus faible sur les variétés résistantes, bien que les gains de poids des insectes aient été les mêmes en 24 h sur IR46 et IR22, les deux étant significativement supérieurs à celui sur IR62.La croissance de la population, l'indice de croissance et le taux de dégâts étaient tous plus faibles sur IR62, ce qui révèle une antibiose et/ou une absence de préférence. Quand la contamination des IR46 a au lieu au stade semis, la croissance de population, l'indice de croissance et le taux de dégâts étaient semblables à ceux de la variété sensible IR22. Quand la contamination avait lieu à un stade ultérieur, le laux de dégâts révélait un niveau modéré de résistance bien qu'une certaine croissance de population se soit maintenue, ce qui révèle antibiose et tolérance.Après exploration de la surface des feuilles des deux variétés résistantes, N. lugens sondait moins fréquemment que sur IR22, ce qui laisse présumer un facteur de résistance associé aux cires superficielles de ces variétés.

     

Seed set in Phormium: interactive effects of pollinator behaviour,pollen carryover and pollen source

Summary Fruit and seed set was studied in New Zealand flax (Phormium tenax Phormiaceae) a large monocot that preferentially sets outcrossed seeds. Fruit set was low and in particular situations could result from insufficient pollinator visitation. Observations of pollinator (Meliphagidae) movements showed that birds preferentially visited male phase flowers and predominantly moved pollen within inflorescences of the same plant. More dominant resident birds moved more between plants that subordinate non-resident birds. Combination of results of fluorescent dye carryover with known bird movements allowed predictions of fruit set and seed size that closely approximated observed levels. Resident birds account for almost half the observed foraging bouts but are predicted to be responsible for the vast majority of the viable seeds.     

Sublethal effects of aldicarb on the behaviour of Aphis fabae and two clones of Myzus persicae and on the transmission of beet mosaic virus by these aphids

In laboratory experiments treatment of sugar-beet plants with aldicarb stimulated the mobility of Aphis fabae and two clones of Myzus persicae which were susceptible (S) and resistant (R) to carbamate-based insecticides, respectively. On the other hand, the number of aphids probing and the total number of probes made was reduced, and hence the transmission of beet mosaic virus (BMV) was restricted. In outdoor experiments the spread of BMV from aldicarb-treated plants by naturally infesting aphids was also restricted. The number of infected plants decreased with increasing distance from the sources of infection.

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Résumé Des plantes de betterave traitées au laboratoire avec de l'aldicarbe ont stimulé la mobilité d'Aphis fabae et de deux clones de Myzus persicae, l'un sensible et l'autre résistant à des insecticides contenant des carbamates. Par ailleurs, le nombre de pucerons en train de sonder les feuilles ainsi que le nombre total de sondages ont été réduits et ainsi la transmission du virus de la mosaïque de la betterave (BMV) a été limitée. Dans des expériences à l'extérieur, la vitesse de propagation de BMV par des pucerons sur des plantes traitées à l'aldicarbe a été aussi plus limitée. Le nombre de plantes contaminées diminuait avec la distance de la source de contamination.

     

Individual variation in the foraging strategies of young yellow perch (Perca flavescens) from the Ottawa River

Differences in the foraging strategies among young individuals of the yellow perch (Perca flavescens) were observed in the laboratory by using two kinds of food (Daphnia and brine shrimp) separately and together. Individuals differed significantly in their ability for feeding attempts, time interval between two consecutive feeding attempts, feeding angles, regurgitation rate, and number of unsuccessful attempts and in their food preference. It is concluded that there are individuals with different foraging strategies. Variability in foraging strategies within single species populations is important because it may explain how the conspecific individuals may differ in their overall feeding behaviour.     

Underwater observations of piranhas in western Brazil

Synopsis The behaviour of three piranha species,Serrasalmus marginatus, S. spilopleura, andPygocentrus nattereri, and their prey fishes was studied underwater in the Pantanal region, Mato Grosso, Brazil. General habits, predatory tactics, feeding behaviour, and social interactions while foraging, as well as defensive tactics of prey fishes were observed.S. marginatus is solitary whereas the other two species live in shoals; their agonistic behaviour varies accordingly, the simplest being displayed by the solitary species. Predatory tactics and feeding behaviour also vary:S. spilopleura shows the most varied diet and highly opportunistic feeding strategy, which includes aggressive mimicry. The solitaryS. marginatus, besides fin and scale-eating, occasionally cleans larger individuals ofP. nattereri. Several cichlid species display defensive tactics clearly related to piranha attacks: tail protecting, watching, and confronting the predator are the most commonly observed behaviours. Piranhas seem to strongly influence use of habitat, social structure, and foraging mode of the fish communities.     

Breeding program for the lesser kudu (Tragelaphus imberbis) in North America

The lesser kudu (Tragelaphus imberbis) has been kept in North American zoological parks since 1930 but has never been a common species in collections. In 1987 this population totaled 28 animals: 15 males and 13 females. A pedigree evaluation in 1987 of the existing population indicated that eight effective founders and one potential founder were represented in the North American herd. Three new potential founders from European captive populations were added to the population in 1987 to increase the number of existing founder lines to 12 animals. As this species is not endangered or threatened in its native habitat, it is not a high priority to qualify for designation as an SSP species. Because of this, the institutions holding lesser kudu in North America decided to join informally and draft a breeding program to better manage this small captive population. This program was designed to minimize inbreeding and equalize genetic representation of founder animals to maximize genetic diversity. It requires a shift in management philosophy to establish stable groups of breeding females at participating institutions while rotating appropriate breeder males through these herds in a controlled manner to ensure minimization of inbreeding and maximization of genetic diversity. It is hoped that this program can serve as a model for the management of other small captive populations of non-SSP species.     

Pollination biology of two species ofKielmeyera (Guttiferae) from Brazilian cerrado vegetation

The pollination biology and breeding systems ofKielmeyera coriacea andK. speciosa, two sympatric woody species common in the cerrado vegetation of C. Brazil, were studied. Both species have similar nectarless, polystemonous Papaver-type flowers which are visited by a similar spectrum of insects, though they bloom in different seasons and are thus phenologically isolated. Large carpenter bees seem to be the most important pollinators and these and other bees effect buzz pollen retrieval despite the fact that anthers are not poricidal. Both species ofKielmeyera possess strong xenogamous breeding systems. The presence of staminate flowers and andromonoecy inK. coriacea, as well as the longevity ofK. speciosa flowers are discussed as alternative strategies to improve pollination success and reproductive efficacy.