Anzeiger für Sch?dlingskunde最新文献

Morphological characteristics of immature developmental stages of Rhyzobius lophanthae Blaisdell (Col.: Coccinellidae), predator of scale insects of the family Diaspididae (Homoptera), are described. Data about the morphology of eggs, the four larval instars, and the pupa is presented. Larval instars are described in more detail: size of head capsule, length of tibia, distribution of dorsal and lateral setae of abdomen segments for each larval instar is reported. Distribution of spiracles is also given. Study on the biology concerns the influence of prey on the duration of instar periods. The diaspidids Aspidiotus nerii and Aonidiella aurantii were used as food. The mean duration of the developmental period from egg to adult was 27.1 days, and no mortality was observed (0 %) when A. nerii was used as prey. The respective numbers when the prey was A. aurantii were 48.8 days and 84 %.

The parasitoids of Gelechia senticetella (Stgr.) (Lepid.: Gelechiidae), a pest of Juniperus excelsa M. B., were studied in the “Tissata” reserve in Bulgaria. They were reared in laboratory conditions from pest larvae and pupae collected in 1991, 1992 and 2000. As a result of this study, 16 species of parasitoids of G. senticetella were recorded: Habrobracon stabilis Wesm., Hormius moniliatus (Nees), Phanerotoma tritoma Marsh. (Hym.: Braconidae), Diadegma consumptor (Grav.), Liotryphon cydiae (Perk.), Scambus pomorum (Ratz.), Scambus foliae (Cush.), Pimpla turionellae (L.), Eudelus simillimus (Tasch.), Mesochorus sp. (Hym.: Ichneumonidae), Sympiesis acalle Walk., Aprostocetus sp. (Hym.: Eulophidae), Eupelmus urozonus Dalm. (Hym.: Eupelmidae), Copidosoma thompsoni Merc. (Hym.: Encyrtidae), Calliprymna bisetosa Grah., and Mesopolobus sp. (Hym.: Pteromalidae). H. stabilis and P. tritoma were discovered as new species for the fauna of Bulgaria. Three species (E. simillimus, Mesochorus sp. and Aprostocetus sp.) are hyperparasitoids, and the remaining species are primary parasitoids. Most of the parasitoid species attack the larvae of G. senticetella and kill the hosts before pupation. In the studied parasitoid complex, D. consumptor and H. moniliatus were the dominant species. In 1991, the level of total parasitism of the host in the “Tissata” reserve was 24.3 %, in 1992 – 57.9 % and in 2000 – 12.7 %. D. consumptor was the most important parasitoid destroying 26.6 % of the pest larvae in 1992.

Methods using the reactions of beneficial arthropods to stimuli of prey and habitats are becoming more and more important in the biological control of pests. Especially olfactory cues, which are measurable with so called ‘olfactometers’ are of great importance. In the present study, a modified four-armed airflow olfactometer is described by explaining these modifications. As an example, the results obtained for the predatory ladybeetle Coccinella septempunctata are explained in detail. Various odour sources caused evident differences in the reactions of the predator, especially comparing the reared beetles and the individuals collected in the field. The volatiles emitted by the odour source ‘bean plant + aphids’ were attractive to 28 % of the reared and to 38 % of the field-collected test individuals. These values were clearly higher than in the cases of the odour source ‘aphids’ with 18 % for both groups. About 15 % of the reared and 13 % of the field-collected coccinellids reacted to the olfactometer chamber without an odour source. On the other hand, it became obvious in test series with groups of adult beetles that group tests were not so suitable because the test individuals diverted each other so that the reactions to the odours were reduced. In the case of the group tests, 68 % of the reared and 60 % of the field-collected individuals did not react to one of the offered odour sources. In further surveys, the most favourable pre-experiment starvation period of the tested individuals and optimal duration for a single experiment were determined. For adults of C. septempunctata, the most favourable starvation time was 6 hours and the most suitable duration of a single experiment 30 minutes. In two further experiments, it was investigated whether there were differences between males and females or between beetles of different ages. There were slight differences between males and females reacting to distinct odour sources and also in the case of coccinellids of different ages but in both cases without clear tendencies.

The green cypress (Cupressus sempervirens) is of great interest for ornamental, reforestation and windbreak use in the whole Mediterranean basin. In Italy, seed material selected for resistance to the fungus Seiridium cardinale is produced in seed orchards by controlled crosses of parent trees. The insect pest showing the highest impact on seed cone production is Pseudococcyx tessulatana (Lep.; Tortricidae), which attacks cones during the initial growth period as well as full-grown cones. The impact on the seed cone crop of the tortricid was estimated on a clone patented for its resistance to cypress canker (Agrimed 1). The attack was inversely related to the cone crop, as it concerned 36.7 % of cones in 1999 (high crop year) and the 66 % in 2000 (low crop year). In both years, about 90 % of the surveyed branches revealed cones attacked by P. tessulatana by the 1^st life-cycle larvae, whereas only 40 % of branches were also attacked by the larvae of the 2^nd life cycle. The highest attack rate per branch was always observed on branches bearing a low number of cones. The potential of two control methods against P. tessulatana to protect cones which result from crossing a mother tree “Agrimed 1” with selected father trees was also evaluated in 2000. The protection given by a sleeve surrounding the branch was almost complete (0.4 % cone mortality), whereas a cone mortality of 24.3 % was observed on branches treated by the insecticide diflubenzuron. Sleeves appear to be useful to protect branches on which special crosses were done, but are expensive and time-consuming and may favour the attack of the mealybug Planococcus vovae inside the sleeve. The insecticide application may represent a valid alternative, especially when protection should be directed toward a high number of branches.

The effect of solarization on the development of Callosobruchus maculatus was investigated in the Nigerian savanna during the hot season from April to May, 1999. Development of C. maculatus adult progeny was completely suppressed in seeds of bambara groundnut, Vigna subterranea bearing bruchid eggs or harbouring first and second instar larvae that were exposed to the sun in metal tins, clay pots or polypropylene sacks for 7, 14 or 28 h. Adults of C. maculatus developed only in seeds that were not exposed to sun. Solarization did not have a significant adverse effect on germinability of bambara groundnut seeds.

Different developmental stages of Microplitis rufiventris Kok. larvae were each exposed to a sublethal dosage (0.4 ppm) of Lefenuron [N-{2,5-dichloro-4-(1,1,2,3,3,3-hexafluoropropoxy)-phenylaminocarbonyl}-2, 6-difluorobenzamide] or Lefenuron/Deltanet [O-n-butylO-(2.2-dimethyl-2, 3-dihydrobenzofuran-7-y1)-N, N’-dimethyl-N-N’-thiodicarbamate] by feeding treated artificial diets to parasitized Spodoptera littoralis (Boisd.) larvae to evaluate their effects on the reproductive potential of resulting parasitoids. Lefenuron treatments caused a great reduction in the reproductive ability of either the host insect or its parasitoid. Ovaries of parasitoid females (1 day old) emerged from Lefenuron/Deltanet treatments contained more ova than those from either Lefenuron or controls. Experienced females from Lefenuron/Deltanet treatments deposited significantly more eggs and contained at death more remaining mature oocytes in their calyx and egg-reservoirs. The combination of carbamate insecticide (Deltanet) and chitin-inhibiting growth regulator (Lefenuron) may enhance the reproductive ability of insect parasitoid and may provide a potential means for developing more effective biological control methods against insect pests.

The polyphagous gypsy moth (Lymantria dispar) is able to feed on about 400 different woody plant species. In general, oak species are preferred – on the other hand some other groups of plants are avoided on account of the presence of toxic substances. These unfavoured hosts are, for example, most of the Papilionaceae, like locust (Robinia pseudoacacia). We compared survival rate and development of two populations of different origin with long-term habituation to oak and locust, respectively. Larvae from the population habituated to oak proved unable to develop on locust food. There must be a lack of detoxification systems to modify the toxic alcaloids and flavenoids produced by Robinia pseudoacacia. On the other hand, larvae isolated from an locust stand were able to feed on oak leaves without problems in larval development or eclosion of adults. Gypsy moth larvae specialized on locust as host showed increased mortality (up to 27 %) in the early larval instars, but the surviving animals, especially female individuals, reached significantly higher pupal weights and showed better fecundity: 40 % higher egg numbers/egg mass compared to those feeding on oak. These results indicate that the gypsy moth population originating from the locust forest had achieved a high level of metabolic adaptation to this host plant and formed a ‘biotype’ of Lymantria dispar with optimal reproductive conditions in this special habitat.

An analysis of the Russian wheat aphid (RWA) (Diuraphis noxia Kurdj.), overpopulated due to extraordinary weather conditions (2000) in the Czech Republic, enabled the identification of several within-field situations ouside of the routine approach. This group, classified as within-field refugium, includes variation due to field relief, some injuries caused by the use of machinery, the unharvested field margins and, last but not least, the volunteer plants. Differences between the RWA populations in these situations and the normal grove are presented and recommended to be taken into consideration in the research on RWA population dynamics and movement.

A study was conducted on the insects infesting seeds and cones of Abies alba Mill. in the Gorce National Park, in southern Poland during 1996 – 1998. A total of 856 cones were collected from 66 trees growing at 11 sites located in partially or strictly protected forest reserves. Of this sample, 217 cones with 54,958 seeds were dissected. This study yielded 5,816 specimens of insects, namely: seminiphagous Resseliella piceae Seitn., Megastigmus suspectus Borr. as well as conophagous Earomyia impossibile Morge, Barbara herrichiana Obr. and Dioryctria abietella (Den. et Schiff.). The most abundant species was R. piceae with 4,186 individuals. The index of cone infestation was calculated. It showed great variability between forest reserves and study-years. The numbers of insect individuals, numbers of viable and infertile seeds, and seeds damaged by M. suspectus and R. piceae, in both strict and partial reserves in the consecutive years were compared statistically. The test of significant differences between two frequencies at 0.05 level was used in statistical analysis. In both strict and partial reserves, statistically significant differences were found between studied variables.