Search

During a 2-year period, 47 species of spiders in 37 genera were taken in pitfall traps set within, or bordering a wheat field near Clavet, Saskatchewan. Species diversity and evenness were determined for the collections from both areas. Lycosids were predominant, both in the field and in the field borders. Seasonal distribution of captures of the two most common species, Arctosa emertoni Gertsch and Pardosa nebraska Chamberlin & Ivie, are given.

Several species of wireworms were attracted to germinating wheat, air from flasks of germinating wheat, decomposing oatmeal, commercial CO2and, in addition, germinating seeds of eight other cultivated plant species. Larvae located a biological or experimental source of CO2by a directed movement along CO2gradients, from distances up to 20 cm.Methods and apparatus for measuring small CO2gradients, using gas chromatography and mass spectrometry, are described.Ctenicera destructor(Brown) larvae apparently responded to CO2gradients between glass plates, that ascended on the average by 0.002% (soil) and 0.005% (agar)/cm over a distance of from 12 to 16 cm. The "sensitivity threshold" was calculated as being 1–2 ppm over the distance involved in one deflection of the head during klinotactic orientation. Attractancy was observed within a range of CO2concentration from about 0.036% to 1.5%. Repellent effects did not appear to be only related to concentration, but possibly were due to steepness of the gradient and(or) previous exposure to CO2.Passing an air stream from germinating grain over a KOH solution eliminated the attractancy of the grain by removing the CO2and possibly other undetected attractants. A small percentage ofC.destructorlarvae apparently oriented to an ethylene source, but it was concluded the CO2was the most important if not the only attractant from germinating wheat seeds.

Determination of the spatial pattern and estimation of the density of egg, larval, and adult populations ofCtenicera destructor(Brown) andHypolithus bicolorEschscholtz were made by soil sampling, and forC.destructoradults, also by cages that collected the emerging adults in the spring. Eggs of both the above species and also those ofAeolus mellillus(Say), which were also found in the samples, were highly aggregated. SmallC.destructorlarvae were most highly aggregated and medium larvae less so; large larvae were usually randomly distributed. UnlikeC.destructor, largeH.bicolorlarvae were more highly aggregated than either the small or mediumbicolorlarvae. Sampling by emergence cages showed thatC.destructoradults were aggregated while sampling by soil cores showed them to be randomly distributed. The different result obtained by the two methods was attributed to the difference in the size of the sampling unit. Aggregation was detected in 29% of theH.bicoloradult population sampled by soil cores only.Larval densities ofC.destructorranged from a low of 0.25 to a high of 1.46 per sample unit (81 cm2) over the 14-year period that samples were taken; densities ofH.bicolorranged from 0.16 to 0.64. Densities ofC.destructorandH.bicoloradults averaged about 6 (range 1–16) % and 12 (0–27) % of the total population of larvae and adults for each respective species. Population composition, in terms of adults and larvae of different sizes, and population fluctuations are discussed.The relation between density and the number of sampling units required to achieve four levels of margin of error at four levels of statistical significance was determined.No satisfactory transformation was found for data of individual samples with a mean less than 1. Several common transformations, including Taylor’s power transformation, were satisfactory for stabilizing the variance of pooled samples.

Oviposition and fecundity of Cteniecra destructor (Brown) were studied in the laboratory and field. In a series of tests, total oviposition by individual field-collected females ranged from 495 to 1464 and averaged from 264.0 to 940.0 eggs per female. Temperatures from 50 to 86° F. had no effect on total fecundity but lower temperatures extended the oviposition period. Soil moisture from 8 to 20% in sifted clay loam soil (particle sine less than 0.177 mm.) had no effect on total oviposition. At 4% soil moisture females died rapidly and laid very few eggs. Food increased the total oviposition, the length of the oviposition period, and the longevity of females. Most eggs were laid during the first month after the onset of oviposition.Oviposition was shown to be cyclic in nature. Females usually laid eggs in large batches, followed by periods when practically no eggs were laid. This resulted in a series of irregular oviposition peaks which gradually declined in magnitude as the oviposition period progressed.

Eggs of Ctenicera destructor (Brown), Ctenicera aeripennis (Kirby) and bisexual and parthenogenetic strains of Hypolithus bicolor Eschscholtz must absorb water to complete embryonic development.In eggs of C. destructor incubated at 24.4 ± 0.5 °C. in sifted soil containing 15% water (wet weight basis), water absorption started during the second day of development and ended within 24 hours. The mean wet weight increased from 26.6 ± 0.2 (standard deviation) μg. to 39.2 ± 0.6 μg. by the third day. During this period the water content increased from 42% to 64%. After the third day, the mean wet weight remained constant but a significant increase (P < 0.01) in the mean water content and a significant decrease (P < 0.01) in the mean dry weight occurred.The progress of water absorption in eggs of C. aeripennis and the two strains of H. bicolor was similar to that in C. destructor. Differences from C. destructor were apparent, however, in the sizes of the eggs, in the initial and final amounts of dry matter and in the water contents.Water absorption by eggs of C. destructor started after one day of incubation at 25 ± 0.5 °C., after 1 to 2 days at 20°, and after 4 days at 15°. The rate of absorption appeared to be slightly more rapid at higher temperatures within the range of 15–25 °C.

Laboratory tests were carried out to determine if certain types of cover and surfaces were preferred by adults of Hypolithus bicolor Eschscholtz. Approximately 45% of the adults selected the rough stone when a rough stone, a smooth stone, a lump of dried manure and a square of paper were provided simultaneously as cover. Soil moisture did not seem to influence this selection, except that the cover in the soil at the highest moisture level was rejected. The selection of preferred cover appears to be in response to thigmo-kinesis coupled with a tendency of beetles to congregate in tight groups under the cover.

Observations on predation of eggs of Hylemya brassicae (Bouché) were made from the Belleville laboratory from 1953 to 1955 as part of a general study of the biotic agents that act against the maggots that attack cruciferous crops. In biological control programs more attention has been given to parasites than to predators. Predation is more difficult to observe and to evaluate and, unlike parasitization, cannot be even roughly appraised by the collection and examination of hosts. As a group, predators are less specific in their food requirements and less regular in their habits than parasites and consequently do not lend themselves so readily to manipulation for biological control purposes. Predators used with success in biological control have had a high degree of specificity to their prey. Non-specific predators may, however, in the presence of large numbers of suitable hosts on which to feed, be important factors in reducing populations of noxious insects. Predation on eggs of H. brassicae is an example.