The Optimum Plant Density for Vigorous Seed Production in Safflower

Seed viability and vigor have been influenced by several factors including soil and climatic conditions, plant nutrition, fertilization, irrigation, plant population and post-harvest storages. The study was conducted to determine the appropriate plant density for vigorous seed production in safflower. The effects of row spacing (14 and 28 cm) and seeding rate (40, 80, 120, 160 and 200 seeds m-2) on yield, yield components and seed quality of safflower were detected in the study. The results showed that increased seeding rates resulted in enhanced seed yield and the highest seed yield was obtained from 14 cm and 200 seed m-2 with 3320 kg ha-1. The row spacing and seeding rate did not cause a significant difference in oil and protein contents. Laboratory emergence, germination after accelerated ageing (AA) and electrical conductivity tests were suitable for determining seed quality among the seed lots, while standard germination, cool and cold tests were not appropriate. The highest laboratory emergence percentage and germination after AA were determined in 80 seed m-2 but field emergence percentage in 120 seed m-2. It was concluded that the 14 cm row spacing and seeding rate of 120 seed m-2 should be advised for high yielding seed production regardless of seed vigor in safflower.

Barley seed sensitivity to water stress at germination stage

Barley seed sensitivity to water and anoxia was tested. Standard germination, mean time of germination (MTG), germination in sand wetted by water to 100% water capacity (anoxia) or by hydrogen peroxide (wet conditions without anoxia), germination in 0.75% hydrogen peroxide and laboratory emergence (15 and 20°C) were evaluated. Barley seed responds sensitively to stress conditions during germination. Significant germination decrease was found in abundance of water. Percentage of reduction depends on the variety and on the year of seed production. Extreme values of water sensitivity are in interval 4–90%. At wetted sand by 0.75%, solution of H₂O₂ the germination was significantly less reduced. That means that barley seed is very sensitive to oxygen deficiency above all and is less injured by quick imbibition. Heterogeneity in seed vigour was demonstrated in laboratory emergence tests. Quick test of germination in 0.75% hydrogen peroxide deserves attention for its high correlation coefficient with the seed laboratory emergence. The results significantly demonstrate a higher sensitivity of deteriorated seed to germination in abiotic stresses conditions. Variability in speed of germination is increasing, which unfavourably extends the mean time of germination.

Parasitism, development and adult longevity of the egg parasitoid Telenomus nawai (Hymenoptera: Scelionidae) on the eggs of Spodoptera litura (Lepidoptera: Noctuidae)

When Telenomus nawai Ashmead or Trichogramma ostriniae Pang & Chen (Hymenoptera: Trichogrammatidae) was inoculated into intact egg masses of Spodoptera litura (Fabricius) that were covered with a scale-hair layer, T. nawai emerged from 76% of the eggs, while emergence of T. ostriniae was from only 3% of the eggs. When the hair layer was removed before inoculation, the rate by the latter increased to 21%. These observations confirmed that the hair layer effectively protects S. litura egg masses from attack by T. ostriniae, and that T. nawai parasitism is more effective. In order to assess the feasibility of T. nawai as a biological control agent for S. litura, parasitism rate, development time and adult longevity were examined in the laboratory. Emergence of T. nawai was observed in more than 95% of 0- and 1-day-old separated eggs of S. litura, but the rate decreased to 60% and 0% for 2- and 3-day-old eggs, respectively. The emergence rates of T. nawai were near 95% for temperatures in a range from 25°C to 35°C, but decreased to 80% at 20°C. No parasitoids emerged at 15°C. The developmental periods decreased as temperature increased from 20°C to 35°C. The developmental threshold occurred at 13.7°C and 13.9°C, and the effective accumulative temperatures from egg to adult emergence were 149.3 and 147.1 degree-days for females and males, respectively. Mean longevity of the adult females decreased with increasing temperature; 87.0 days at 15°C and 9.5 days at 35°C. The feasibility of the use of T. nawai for controlling S. litura is discussed.

Emergence of Spring- and Summer-planted Onions following Osmotic Priming

The effect of osmotic priming on onion (Allium cepa L.) seedling emergence was evaluated in the field and in a controlled environment at 15C. Seeds of onion cultivars Bronze Wonder, Challenger, Big Mac, and White Keeper were primed in a solution of 300 g polyethylene glycol 8000/liter for 7 days at 10C 1 to 2 weeks before being planted in Spring 1986 and Summer 1987. Time to 50% of maximum emergence (T) for seedlings from primed seeds averaged 10% to 12% less than for unprimed seeds in both seasons and in laboratory experiments. Maximum emergence was improved 7% by priming in one spring field experiment but not in the summer field experiments or in the laboratory. Differences in T among cultivars in the 1986 experiments were small and significant only in one laboratory experiment. In 1987, cultivar differences in T were significant but not consistent in all experiments. Cultivar T means from laboratory experiments were significantly (P = 0.05) correlated with those for field emergence in three of four experiments, but coefficients were low (r = 0.37 to r = 0.45). Values for maximum emergence in the laboratory were not correlated with maximum emergence in the field. Laboratory emergence tests at 15C were a poor predictor of field emergence. Seed priming may benefit establishment of spring-seeded onions emerging at soil temperatures ≤ 15C more than summer-seeded onions emerging in soils >24C.

Patterns of Larval Emergence and Their Potential Impact on Stock Differentiation in Beach Spawning Capelin (Mallotus villosus)

The environmental cues triggering larval capelin (Mallotus villosus) emergence in the St. Lawrence estuary and in coastal Newfoundland are different. In the estuary, emergence from the intertidal and subtidal spawning grounds starts with dusk and ends with dawn, indicating an active response to low light intensity. In the laboratory, emergence from undisturbed sediments collected in the field is perfectly synchronized with the dark phase of the illumination cycle. Nocturnal emergence would represent an adaptation reducing vulnerability to visual predators. Previous work has shown that in Newfoundland, capelin emergence from intertidal beaches is triggered by abrupt changes in water temperature following the sporadic advection to the coast of surface water masses characterized by low predator and high prey abundances. We argue that regional differences in the emergence pattern of the species represent different strategies to avoid predation at the onset of the planktonic drift when the vulnerable yolk sac larvae are densely aggregated. Selection acting on the behaviour of the early larval stages could contribute to stock differentiation in capelin.

Seasonal fluctuations of Culicoides species (Diptera: Ceratopogonidae) in Kenya

Light-traps were used to collect adult Culicoides from 61 sites throughout Kenya and to sample long-term population fluctuations at six sites. Activity patterns were recorded with a suction trap and larval habitats were sampled with laboratory emergence traps. Culicoides cornutus De Medllon, C. milnei Aust., C. pallidipennis C, I. & M., C. schultzei (End.) gp. and C. zuluensis De Meillon were found widespread and also concentrated at livestock pens. Their seasonal population fluctuations did not correlate clearly with rainfall but all these species persist throughout the year. The activity of C. pallidipennis and C. schultzei gp. extends over the whole night and is inhibited by winds in excess of 3 m/s and stimulated by high temperatures and relative humidity. Larval habitats were mainly in mud mixed with detritus or dung; larvae of C. pallidipennis and C. schultzei gp. were both found in swamp mud but not in dung pats. The significance of these findings is discussed in relation to the epidemiology of bluetongue virus disease of sheep and ephemeral fever virus disease of cattle.

Laboratory Emergence of Adults from Overwintering Pupae of the Apple Maggot, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae)

Emergence in the laboratory at 80°F. of apple maggot adults from pupae overwintering outdoors was compared at different times of the dormant period and with emergence from pupae stored at 37-40° for all or varying parts of the dormant period. Shorter incubation times were required for emergence when pupae from outdoors were placed in incubation in autumn, one to three months after larval maturity, than during winter or early spring. Exposure for at least six weeks to low temperatures, either outdoors or in the laboratory, at first increased the incubation time required for emergence. Later the required incubation times of insects overwintering outdoors or in the refrigerator decreased as the duration of exposure to low temperature (or duration of dormancy) increased. But no such decrease was evident in samples of pupae held at 37-40°F. for periods longer than six months. Comparison of emergence from pupae from outdoors with those stored at 37-40°F. when incubated in spring and early summer showed that outdoor temperatures before June 1, in 1959-61 at least, had no effect on the subsequent emergence from pupae overwintering outdoors. When incubation at 70°, 75°, 80°, 85° and 90°F. was compared, the times required for emergence decreased with increased incubation temperature up to 85°F. However incubation at 90°F. resulted in a decrease in the percentage of incubated insects that emerged as adults.

The Emergence of the Cercariae of Fasciola hepatica from the Snail Limnaea truncatula.

1. Observations on Fasciola hepatica in Limnaea truncatula under laboratory conditions showed that the cercariae did not emerge at temperatures below 9°C. Above 9°C. emergence proceeded indiscriminately up to the limit of experimental observation (26°C).2. Experience showed that emergence occurred in the light or in darkness while changes in the hydrogen-ion concentration of the water containing the snails (within the range 5.5 to 8.5) had no effect on emergence. There was some evidence that an increase of carbondioxide in the water slowed but did not inhibit emergence but depletion of oxygen had no apparent effect.3. In the laboratory, emergence could be induced by removing snails from dry habitats and immersing them in water or by removing snails from watery habitats and placing them in fresh water. We were unable to determine the exact physical.or chemical factors acting as a stimulus under such conditions.