Staffan Wiktelius

Can polyphagous predators control the bird cherry-oat aphid (Rhopalosiphum padi) in spring cereals?: A simulation study

Predation by two carabid species, Bembidion lampros (Herbst.) and Pterostichus cupreus L., on the cereal aphid, Rhopalsiphum padi L., was described using a discrete event simulation model. The results were incorporated into an aphid population growth model. The aphid model was run using actual temperatures, R. padi emigration rates, field densities and distributions from three years with distinctly different aphid population levels. Predation was incorporated at different time periods. Predation during the arrival of emigrants and establishment of aphid populations had approximately the same effect as predation over the entire aphid period, whereas predation during the 20 days prior to peak had very little effect on resulting peak populations. We conclude that a) yearly levels of R. padi infestation are mainly determined by the volume and intensity of emigrants; b) peak levels are sensitive to changes in predator density; and c) in some cases an outbreak of R. padi may be prevented by the action of spring active polyphagous predators alone.

Simulations of bird cherry—Oat aphid population dynamics: A tool for developing strategies for breeding aphid-resistant plants

A model of the population dynamics of the bird cherry—oat aphid (Rhopalosiphum padi (L.)) has been used to study the likelly effects of plant resistance on aphid population growth. The sensitivity to changes in aphid population variables (landing, wing formation, birth, mortality, development) and their timing were simulated. Based on the simulations, we suggest that resistant plant genotypes should have the following characteristics in their effects on the aphid: (i) cause high nymphal mortality, (ii) cause prolonged development during early plant stages and (iii) cause low birth rate close to ear emergence. The simulations also stress the need for further research on the damaging effects of R. padi on the plant.

Organochlorine Insecticide Residues in African Fauna: 1971–1995

Organochlorine insecticides (OCLs), which were introduced in the decade following World War II, were used extensively in Europe, the U.S., and other developed countries into the 1970s. However, data began to accumulate on their persistence in soils and aquatic sediments, their potential to be taken up into animal tissues and to bioconcentrate in birds and mammals in the higher tropic levels of food chains and even in humans. As a result, registration authorities phased out their use progressively, in Europe and the U.S., from 1973 onward. However, the production of OCLs in developed countries and their use in developing countries continued through the 1970s and 1980s into the 1990s because they were, no longer under patent agreement, were inexpensive to manufacture, and were very effective in pest control. In Africa, the use of OCLs continued well into the 1990s for the control of mosquitoes, tsetse flies, and desert locusts as well as to combat various crop, animal, and human pests. Some of these uses involved extensive spraying of large areas of nonagricultural land, thereby exposing many groups and species of wildlife to their residues. Although there is some evidence of a gradual decline in the use of OCLs in Africa, they are still being used in appreciable quantities. During the past 25 yr, there have been 50 published reports of OCL residues in the various groups of invertebrate and vertebrate animals constituting the African fauna. These have been based on a diverse range of surveys, target animals, sampling methods, and analytical techniques. Moreover, they are extremely regionally-biased, the most intense surveys being in Zimbabwe, Kenya, Egypt, and South Africa. DDT was the most commonly used OCL, accounting for about half the total use, followed closely by dieldrin and HCH. Birds and fish have been sampled most intensively, with relatively few studies on other taxa. We reviewed the OCL residue data on African fauna from these reports and summarized the maximum and mean residues in the various groups of terrestrial and aquatic invertebrates and vertebrates. Overall, residues in the fauna were the greatest for DDT, followed in turn by those of dieldrin, HCH, endosulfan, and endrin, with small amounts of aldrin and toxaphene being found in some animals. There were relatively few reports of OCL residues in terrestrial invertebrates and virtually none in aquatic invertebrates. Only a few reports demonstrated OCL residues in terrestrial vertebrates, although high levels of DDT, dieldrin, and HCH were found in crocodile eggs and large residues of dieldrin occurred in bats, squirrels, and monkeys. Considerable OCL residues were reported in a few species of fish, especially Barbus, Clarias, Hydrocynus, Labeo, Sarotherodon, Epiplatys, and Synodontis. These residues were at levels that could have caused chronic toxicity or behavioral changes. The calculated maximum and mean OCL residues in the various elements of the African fauna until 1995 were compared with those calculated for corresponding faunal groups in Europe and the U.S. from their development and introduction up to 1973. The OCL residues reported in African fauna between 1971 and 1975 tended to be significantly higher overall than those published for Europe and the U.S. In particular, residues of DDT and dieldrin in African birds and their eggs were greater than those that had been incriminated as causing significant eggshell thinning and reproductive failure in European and U.S. aquatic and terrestrial birds up to 1973. Additionally, high DDT and dieldrin residues were reported from some species of African fish at levels that could potentially affect their reproduction, have chronic toxic and behavioral effects, and even drastically affect populations. Holistic case studies on the use of OCLs to control tsetse flies and desert locusts were discussed. OCL levels in trophic levels of fauna associated with Lake Kariba (between Zambia and Zimbabwe) were summarized. (AB

Long range migration of aphids into Sweden

A five year study of migration of aphids across the southern part of the Baltic Sea is reported. The aphids were caught in a suction trap placed on a lighthouse 50 m from the shoreline. Large sections of the results are presented as case studies i.e. catches of aphids from periods containing at least three consecutive days with a southerly gradient wind. Some periods contained large and diverse catches and it is assumed that aphids regularly cross the Baltic Sea. The catches was largest on days when a cold front passed the trapping site within a period. MoreMyzus persicae were caught on days when the wind was southerly than on days with a northerly wind direction.

The influence of slope aspect and soil type on immigration and emergence of some northern temperate dung beetles

Summary Soil type is a habitat factor that influences both adult habitat choice and reproductive success in tropical dung beetles. However, soil type habitat preferences of northern temperate dung beetles have not been studied, nor has their reproductive success in relation to habitat heterogeneity been investigated. The aim of this study was, firstly, to study the impact of slope aspect (southern vs. northern) and soil type (sand vs. clay) on immigration and subsequent emergence of dung beetle offspring. A second aim was to evaluate whether the soil type selection was reflected in reproductive success. The study was performed with cow dung during early summer in central Sweden. Beetle immigration was estimated using dung-baited pitfall traps and numbers of emerging beetles were assessed using specially designed emergence traps. Immigrating beetles collected represented 11 Aphodius species (Scarabaeidae), three Sphaeridium species (Hydrophilidae), and one Geotrupes species (Geotrupidae). Seven emerging species were caught, all from the genus Aphodius. Immigration was influenced by soil type, i.e. more individuals of A. ater, were caught on clay while more individuals of A. haemorrhoidalis were caught on sand. Slope aspect had no significant influence on immigration. Four species (A. ater, A. fimetarius, A. fossor and A. pusillus) dominated amongst the emerging beetles at both sites. Emergence was earlier on the south-facing slope for A. fimetarius and on both the south-facing slope and on sand for A. fossor. Emergence patterns were dependent on soil type. More individuals of A. ater emerged on clay while more individuals of A. fossor and A. pusillus emerged on sand. Slope aspect did not significantly influence the number of emerging beetles. We conclude that soil type influenced both adult habitat selection and reproduction, while slope aspect had less effect. Patterns of immigration and emigration corresponded for some species but not for others, hence selection of soil type may not directly correspond to reproductive success. Our results also indicate that Aphodius reproduction may be risky in wet clay soils because of mortality in over-wintering individuals.

Wind dispersal of insects

Abstract Three examples of wind dipersal of insects into Sweden from south are given, two concerning aphids and one the Colorado beetle. The wind dispersal is regarded as important as a way of increasing the area of distribution for the insect species and in plant protection for man.

Impact of chlorpyrifos used for desert locust control on non-target organisms in the vicinity of mangrove, an ecologically sensitive area

Ecologically sensitive areas (ESAs) including the mangrove along the Red Sea Coast of Sudan may be subjected to adverse impacts of insecticides for controlling desert locust, Schistocerca gregaria (Acrididae). This study assessed potential impacts of an aerial application of chlorpyrifos (Ultra Low Volume [ULV], 279 g a.i. ha−1) during conditions resembling an operational treatment of desert locust. The surveyed non-target organisms were studied in one treated and one untreated area (88 ha each), during a 13-week pre-spray period and an 8-week post-spray period, from November 2001 to April 2002. Survival of caged prawns (Penaeidae) in the mangrove lagoon were tested in situ, and monitoring of relative abundances of non-target organisms included (i) terrestrial transect counts of hoopoe larks, Alaemon alaudipes (Alaudidae), and of antlion larval pits, Cueta spp. (Myrmeleontidae) and (ii) pitfall sampling of epigeal arthropods in the terrestrial zones from shore to cropland. The survival of Metapenaeus monoceros juvenile prawns fell dramatically between the third and fifth day after the application in the treated area compared to the untreated area, in which mortality was delayed. In the early mornings when control operations often occur, a northern and northwestern wind direction, i.e. from land towards the sea, dominates, thus adverse impact on the prawns is a risk. The abundance of antlion pits was reduced in the treated area following spraying, but not in the untreated. The same was true for observations of hoopoe larks, numbers of Mesostena angustata (Tenebrionidae), and Gryllus bimaculatus (Gryllidae), at species and family levels, and arachnids.

Tethered flight of Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae)

Static tethered flight was used under laboratory conditions to investigate the flight duration of Chilo partellus (Swinhoe). A flight mill was used to measure flight velocity. Mated females flew for a longer time than unmated ones. Females also flew for a longer time than males. Mated females were able to fly and lay eggs alternately for at least three nights in a row. Flight did not affect the number of eggs deposited by females. The results from the flight mill show that the mill is an accurate device to measure flight velocity. The airspeed of C. partellus proved to be 0.9 m/s, and there appeared to be no difference between the flight velocity of mated or unmated males and females.