Mehrjaehrige Untersuchungen zum Auftreten von Getreideblattlaeusen und natuerlichen Antagonisten in Winterweizen und deren Beeinflussung durch verschiedene Bekaempfungsmassnahmen

Available from TIB Hannover: DB 4337 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Relationship between management practices, fungal infection and aflatoxin for stored maize in Benin

This study relates preharvest and harvest practises to postharvest quality of maize in Benin, West Africa. Fungal infection and aflatoxin levels were evaluated in 300 farmers’ stores in four agro‐ecological zones over 2 years (1993–1995), at the beginning of storage (sample A) and 6 months later (sample B). Aspergillus flavus infected 10–20% of the kernels in sample A (1993–1994). In sample B, 54–79% of the kernels were infected with A. flavus. In 1994–1995, A. flavus infection was higher in sample A (27–47%) than B (8–26%). Fusarium species were found in 38–58% of the kernels in sample A in both years, but decreased slightly to 29–51% in sample B. Significant agroecozonal effects existed within sampling, but were not consistent between samplings and years. Of the total number of samples collected (744), 38.8% were found to be aflatoxin‐positive, with an average of 105 parts per billion (ppb) and 60% of the aflatoxin‐positive samples having a contamination approximately 20 ppb, the intervention level recommended by the World Health Organization. Factors associated with increased aflatoxin were: planting local maize varieties in southern Benin, intercropping with cowpea, groundnut, or cassava, use of urea‐fertilizer, damage to maize in the field, prolonged harvesting, long drying periods in the field, and winnowing. Practices that reduced aflatoxin contamination were: planting improved varieties in northern Benin, mixed cropping with vegetables, use of NPK‐fertilizer, drying of harvested cobs for 60–90 days, drying ears without the husk, sorting out of poor quality ears

Factors affecting the biology of Telenomus isis (Polaszek) (Hymenoptera : Scelionidae), an egg parasitoid of cereal stem borers in West Africa

Published online: 25 May 2002This study aimed at an assessment of the potential of the egg parasitoid Telenomus isis (Polaszek) as a biological control agent of cereal stem borers. Therefore, the effects of temperature, host species, host age, and time of host deprivation on the development and the reproductive potential of T. isis were studied in the laboratory. By use of linear regression and a modified Logan model and with eggs of the noctuid Sesamia calamistis Hampson as hosts, the lower and upper thresholds for development were estimated at 13.1 and 36°C, respectively, and the optimal temperature for development was 31°C. Female T. isis had no measurable preoviposition period, and the oviposition period ranged from 3 to 5 days. Approximately 66% of the total lifetime complement of eggs of T. isis were produced within 6 h after emergence. Average total lifetime fecundity was 61.1 and 82.1 eggs per female at 21 and 28°C, respectively. Longevity of adult females was 17.1 days at 21°C and 5.2 days at 30°C. Host acceptance and suitability were tested, using nine lepidopteran borer species. Only the noctuids S. calamistis, Sesamia poephaga (Tam & Bowden), Sesamia botanephaga (Tam & Bowden), and Busseola fusca (Fuller) were successfully attacked by T. isis. Parasitism and emergence did not differ among those species, but the sex ratio (expressed as proportion of female progeny) was significantly lower on S. calamistis. An increase of the host age from 1 to 4 days significantly reduced mean parasitism from 56.7 to 23.5%. Parasitoid emergence rates and sex ratio did not vary among 1-, 2-, or 3-day-old host eggs, but both parameters were significantly lower on 4-day-old eggs. With increasing duration of host deprivation from 0 to 17 days, longevity increased from 8.5 to 18.5 days, whereas average lifetime fecundity decreased from 81.2 to 40.5 eggs per female, respectively, indicating resorption of eggs. The results are discussed and compared with life table parameters of the ubiquitous egg parasitoid Telenomus busseolae (Gahan)

Host location and host discrimination behaviour of Telenomus isis ( Polaszek) (Hymenoptera : Scelionade) an egg prarsitoid of the African cereal stem borer Sesamia calamistis Hampson (Lepidoptera: Noctuidae)

In the Republic of Benin, the scelionid egg parasitoid Telenomus isis (Polaszek) is one of the most important control factors of the noctuid maize stem borer Sesamia calamistis. In the present study, the role of various sources of contact kairomones (male or virgin or mated female moths) and of the moth's oviposition substrate (leaf sheath versus filter paper; host plant species) in host location and oviposition behavior of T. isis was investigated in Munger cells, open arenas, and/or Petri dish assays. Furthermore, its ability to distinguish between unparasitized eggs and eggs parasitized by a conspecific female or by the trichogrammatid Lathromeris ovicida was studied. In the Munger cell experiment, T. isis spent more time in moths' odor fields than in the control. There was no difference between virgin and mated females. In the open arena assay, traces left by both the male and female moths acted as contact cues, which elicited an arrestment response in the parasitoid. The residence and patch retention time in the arena with virgin or mated females of S. calamistis was about 4.8 times as long as that with males. The presence of maize leaf sheaths stimulated the oviposition behavior of T. isis when compared to eggs offered on filter paper. During the first 6 hr, more eggs were parasitized on maize leaves, although there was no difference in the final number of offspring between the two substrates. In addition, if eggs of S. calamistis were offered together with different host plant species or alone, maize and sorghum were both more attractive than millet or the egg alone and equally attractive between themselves, indicating that the plant tissue influences host finding of T. isis. Both T. isis and L. ovicida recognized markings of conspecific females, and intraspecific superparasitism was therefore low. Interspecific superparasitism was more than three times higher for L. ovicida than for T. isis, indicating that only T. isis was able to recognize the marking of the other species and tried to avoid superparasitism. Emergence of parasitoids from multiparasitized eggs generally was in favor of L. ovicida regardless of species order

Infestation of maize by Prostephanus truncatus initiated by maleproduced pheromone

Delta traps baited with maize cobs, which were infested each with one male Prostephanus truncatus (Horn) (Col.: Bostrichidae), were distributed in southern Benin and collected after one, two, three and four weeks. The numbers of P. truncatus caught during the different trapping periods were not significantly different. Sixty‐four percent of the trapped P. truncatus were females. Females attracted during the one‐week trapping period produced a mean of 6.9 progeny during the seven days. The sex ratio of the progeny was 1:1. Trap catches with the infested cobs were on average 13 times lower than catches with 2 mg of the artificial pheromone. Estimation of P. truncatus densities in a maize store at the beginning of the storage period (based on laboratory data) revealed that small initial numbers of P. truncatus, possibly attracted by a single male, sufficed to initiate high infestation rates later in the storage seaso

Bionomics of Mussidia nigrivenella (Lepidoptera: Pyralidae) on three host plants

Life table studies of Mussidia nigrivenella Ragonot, a pest of maize in Benin, showed that host plant species had a significant effect on larval survival and developmental time. The maximum percentage of larvae surviving was recorded on jackbean, Canavalia ensiformis (36%) and lowest on maize (18%). Mean developmental time for larvae was longest on maize (19.8 days) and shortest on jackbean (17.2 days). The number of eggs laid was highest for females from larvae fed on jackbean (x– = 176), followed by velvetbean, Mucuna pruriens (x– = 143), and lowest for females where larvae had fed on maize (x– = 127). Longevity of ovipositing females was higher on jackbean (5.4 days) than of those from any other host plants. According to the growth index and life table statistics, jackbean was the most suitable host plant, followed by velvetbean, and maize, the least suitable. Thus, jackbeans should be recommended for use in mass rearing programmes of M. nigrivenella, e.g. as a host for parasitoids in future biological control programmes. Because of the high suitability of jack- and velvetbeans for M. nigrivenella, planting of these increasingly important cover crops should be timed in such a manner that the emergence of female moths from mature pods does not coincide with maize plants in a suitable developmental stage for oviposition and development of young M. nigrivenella larva