Dormancy of Heterodera glycines in Missouri

A 2-year study was conducted in field microplots to determine the relative importance of soybean phenology and soil temperature on induction of dormancy in Heterodera glycines in Missouri. Four near-isogenic soybean lines differing for maturity date were planted in microplots infested with a race 5 isolate of H. glycines. Soil temperature was monitored at a depth of 15 cm. Eggs of H. glycines, extracted from cysts collected monthly from each microplot, were used in hatching tests and bioassays to determine dormancy. Egg hatching and second-stage juvenile (J2) infectivity rates decreased sharply from their highest levels in midsummer (July-August) to a low level by October of each year and remained low (< 10% hatching and < 0.2 J2/cm root) until May or June of the following year. The patterns of numbers of females and eggs in the bioassays were similar. The decreases were not related to soil temperature and did not differ consistently among soybean isolines. The monophasic changes in all nematode responses with peak midsummer rates suggest that H. glycines produces one primary generation per year in central Missouri. Changes in hatching rates and the timing of minimum and maximum rates suggested that H. glycines eggs exhibit more than one type of dormancy.     

Egg-shell calcium and the hatching of Globodera rostochiensis

The Ca²⁺ content of Globodera rostochiensis egg-shells was investigated by X-ray microanalysis. When intact eggs were treated with 5 mM sodium 1, 2-di (2-aminoethoxy) ethane-N,N,N',N',-tetra-acetate (EGTA) only part of the egg-shell Ca²⁺ was removed. Similarly treated opened egg-shells lost almost all their Ca²⁺. We think that Ca²⁺ of intact egg-shells which is accessible to EGTA is in the outer part of the shell and that the inaccessible Ca²⁺ is in the inner lipoprotein layer. Much Ca²⁺ was removed from opened egg-shells by the hatching agents Zn²⁺, La³⁺ and decationised potato-root exudate, but none by dilute acetic acid or Mg²⁺. Hatching agents, by binding to or replacing Ca²⁺, may change lipoprotein membrane structure. Eggshells treated with potato-root exudate contained about 3 times as much Ca²⁺ as untreated shells, because the treatment makes additional binding sites available. Our results suggest that three types of Ca²⁺ -binding sites occur in the egg-shell.     

Asynchronous hatching provides females with a means for increasing male care but incurs a cost by reducing offspring fitness

In species with biparental care, sexual conflict occurs because the benefit of care depends on the total amount of care provided by the two parents while the cost of care depends on each parent's own contribution. Asynchronous hatching may play a role in mediating the resolution of this conflict over parental care. The sexual conflict hypothesis for the evolution of asynchronous hatching suggests that females adjust hatching patterns in order to increase male parental effort relative to female effort. We tested this hypothesis in the burying beetle Nicrophorus vespilloides by setting up experimental broods with three different hatching patterns: synchronous, asynchronous and highly asynchronous broods. As predicted, we found that males provided care for longer in asynchronous broods whereas the opposite was true of females. However, we did not find any benefit to females of reducing their duration of care in terms of increased lifespan or reduced mass loss during breeding. We found substantial negative effects of hatching asynchrony on offspring fitness as larval mass was lower and fewer larvae survived to dispersal in highly asynchronous broods compared to synchronous or asynchronous broods. Our results suggest that, even though females can increase male parental effort by hatching their broods more asynchronously, females pay a substantial cost from doing so in terms of reducing offspring growth and survival. Thus, females should be under selection to produce a hatching pattern that provides the best possible trade‐off between the benefits of increased male parental effort and the costs due to reduced offspring fitness.     

Living at the edge: lower success of eggs and hatchlings at lower elevation may shape range limits in an alpine lizard

Studies on range limits clarify the factors involved in the extent of species occurrence and shed light on the limits to adaptation. We studied the effects of elevational variation on the thermal dependence of fitness‐related traits (incubation time, hatching rate, and survivorship, size, and condition of hatchlings) to assess the role of incubation requirements in distribution range limits of the alpine endemic Iberolacerta cyreni. We captured gravid females from two core (summit) and two marginal (low‐elevation edge) populations, we incubated their eggs at three temperatures (22, 26, and 30 °C), and we monitored phenotypic effects. Viability of eggs and hatchlings decreased, independently of elevation, as incubation temperature increased. Hatching success and embryo survivorship were lower for clutches from low‐elevation areas than for those from mountain summits, showing that lizards face difficulties thriving at the low‐elevation edge of their range. Such difficulties were partly counterbalanced by faster postnatal growth at lower elevations, leading to increased adult size and higher fecundity. High incubation temperature had detrimental effects also at low‐elevation areas, and no elevational variation in the thermal dependence of hatchling traits was detected. We suggest that temperature effects on egg development and the lack of selective pressures strong enough to foster local adaptation at marginal areas, combined with extended egg retention, may contribute to shape the range limits of these alpine oviparous reptiles.     

Migratory herds of wildebeests and zebras indirectly affect calf survival of giraffes

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Effects of Aldicarb on the Behavior of Heterodera schachtii and Meloidogyne javanica

The toxic effects of sublethal concentrations ofaldicarb were studied on eggs and second-stage larvae and males of Heterodera schachtii and second-stage larvae only of Meloidogyne javanica in a quartz sand substrate. Aldicarb was more toxic to eggs of H. schachtii than to those of M. javanica. Complete suppression of hatching occurred between 0.48 and 4.8 μg/ml aldicarb for H. schachtii whereas 100% inhibition of hatch of M. javanica occurred between 4.8 and 48.0 μg/ml. M. javanica hatch was stimulated at 0.48 μg/ml aldicarb. Migration of second-stage larvae of H. schachtii and M. javanica in sand columns was inhibited under continuous exposure to 1 μg/ml aldicarb. Infection of sugarbeet and tomato seedlings by larvae was inhibited at 1 μg/ml. H. schachtii males failed to migrate toward nubile females at 0.01 μg/ml aldicarb. This was partially confirmed in a field study in which adding aldicarb to soil resulted in fewer females being fertilized.     

Development and Fecundity of Reesimermis nielseni,a Nematode Parasite of Mosquitoes

Maturation of the mermithid nematode Reesimermis nielseni to the adult stage began by the tenth day after emergence of the nematodes from their hosts at ambient temperatures (24-27 C). Most postparasitic males and females reached the adult stage after 50 and 70 days, respectively. The first females exhibiting egg development and oviposition were observed 25-30 days after emergence, but some oviposition was still taking place 150 days later. Reesimermis nielseni laid an average 2,480 eggs per female over an 18-day oviposition period. A majority of the mature eggs hatched within 7 h after the cultures were flooded. The preparasites are short-lived, and only a few were able to infect exposed hosts after 72 h.     

A method for hatching the eggs of the aphid Schizaphis graminum

Techniques are described for the collection of fertile eggs of Schizaphis graminum (Rond.) on filter paper, and for the subsequent sterilization and incubation of the eggs under various temperature and photoperiodic conditions.19% of the eggs incubated continuously at 16°C in complete darkness hatched in 81 days after deposition. 45% of the eggs chilled at 6°C for 40 days (starting 10 days after deposition) hatched in 71 days if the postchilling incubation at 16°C was completed in darkness. The results indicate a further enhancement in the percentage egg hatch and a reduction in developmental time when the eggs were subjected to a light-dark regime during the post-chilling incubation.

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Zusammenfassung Es wird eine einfache und effektive Methode beschrieben, die Eier von Schizaphis graminum auf Filterpapier zu sammeln, sie nachfolgend zu sterilisieren und unter verschiedenen Temperatur- und Photoperiodebedingungen bis zum Schlüpfen zu inkubieren.Hierbei wurden folgende Resulate erzielt: (a) Inkubation der Eier in vollkommener Dunkelheit bei 16°C führte zu einem Schlupferfolg von 19% nach einer Entwicklungszeit von im Mittel 81 Tagen; (b) Kühlung der Eier bei 6°C während 40 Tagen (vom 10. Tag nach der Eiablage an) erhöhte die Schlupfrate unter ansonsten gleichen Bedingungen auf 45% und reduzierte die Entwicklungszeit auf 71 Tage; (c) durch einen Licht/Dunkel-Rhythmus, dem die Eier nach der 40-tägigen Kühlung ausgesetzt wurden, konnte eine weitere Steigerung der Schlupfrate und eine Verkürzung der Entwicklungszeit erreicht werden.

     

Pathological Differences in Heterodera schachtii Populations

Five populations of Heterodera schachtii Schm. from Oregon, Idaho, and Utah did not differ significantly in seedling penetration and rate of emergence and virulence. Another Utah H. schachtii population (Utah 2), however, differed from these five populations in all of the above-mentioned characteristics. More H. schachtii larvae of the Utah 2 population than the other populations penetrated sugarbeet seedlings at 10, 15, 20, and 25 C. Root and top weights of sugarbeet plants were signiticantly less when roots were parasitized by the Utah 2 population than when they were parasitized by larvae of the other nematode populations under similar experimental conditions. Also, the period of larval emergence was shorter in the Utah 2 population than in any of the other H. schachtii populations.     

Hatching ofCoregonus albula andC. lavaretus embryos at different stages of development

Synopsis Hatching in Coregoninae embryos is not closely connected with a determined stage of embryonic development. Electrical stimulation (AC) induced precocious hatching, and incubation at low temperature caused delay of hatching compared to controls. Embryos hatched precociously had shorter bodies and larger yolksacs than those whose hatching was normal or delayed. This was accompanied by respective changes in duration of the eleutheroembryonic phase (DEP) — inCoregonus lavaretus DEP decreased from 7 days in embryos hatched precociously to 0 days in embryos from delayed hatching.