Are the palms Washingtonia filifera and Chamaerops humilis suitable hosts for the red palm weevil,Rhynchophorus ferrugineus (Col. Curculionidae)?

The red palm weevil, Rhynchophorus ferrugineus (Olivier) (Coleoptera, Curculionidae), is a widely distributed pest which has recently become the major pest of palms in the Mediterranean Basin. This weevil has been recorded on 19 different palm species, however, the host status of Washingtonia filifera and Chamaerops humilis remains unclear. The present study was carried out to check whether these species had either antixenotic or antibiotic mechanisms of resistance against this pest. Our results show that both W. filifera and C. humilis are resistant to R. ferrugineus. Resistance in W. filifera is based on antibiosis whereas in C. humilis resistance is based on antixenosis.     

Genetic Analysis of Bemisia (Hemiptera: Aleyrodidae) Populations by Isoelectric Focusing Electrophoresis

Twenty-one whitefly populations in the genus Bemisia were evaluated for genetic variation at 3 allozyme loci. Nine of the 22 populations that exhibited polymorphic loci were subjected to allozyme analysis using a minimum of 10 enzymes, representing 10 to 14 distinct loci. Among those nine variants examined, calculated genetic distances ranged between 0.03 and 0.52, with three main groups emerging from the analysis. One group comprised two closely related Western Hemisphere variants of B. tabaci: type A from California, United States and a geographically proximal population from Culiacan, Mexico. A second cluster contained five collections previously identified as B. tabaci type B and Bemisia argentifolii, while a third group contained a single population from Benin, Africa. The latter two groups were grouped separately from New World populations and are thought to have a recent origin in the Eastern Hemisphere.     

Resistance of wild Lycopersicon species to the potato moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)

Abstract  Trichome-based host plant resistance of Lycopersicon species to potato moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), was examined in a laboratory bioassay. Neonate P. operculella were placed on the foliage of accessions of L. hirsutum , L. hirsutum f. glabratum , L. pennellii , L. cheesmanii f. minor and L. esculentum for 48 h . At the end of this period, larval mortality, the numbers of larvae emigrating from, and mining into, the leaf surface were recorded as were leaf area and the densities of trichomes. Analysis by categorical logistic regression found accessions differed in levels of resistance to P. operculella ( P  < 0.001). Further analysis using generalised linear models showed mortality was associated with high densities of type VI and low densities of type V trichomes; emigration from the leaf was associated with high densities of type I and type VII trichomes; and the numbers of mines associated with low densities of type I and type VI trichomes and increased leaf area. Although results indicate that certain accessions of L. hirsutum and L. hirsutum f. glabratum may be most appropriate for inclusion in a breeding program aimed at introducing trichome-based host plant resistance of wild Lycopersicon species into the tomato, further research is necessary to fully understand the mechanisms.     

Genetic mapping of three quantitative trait loci for soybean aphid resistance in PI 567324

Host-plant resistance is an effective method for controlling soybean aphid (Aphis glycines Matsumura), the most damaging insect pest of soybean (Glycine max (L.) Merr.) in North America. Recently, resistant soybean lines have been discovered and at least four aphid resistance genes (Rag1, Rag2, Rag3 and rag4) have been mapped on different soybean chromosomes. However, the evolution of new soybean aphid biotypes capable of defeating host-plant resistance conferred by most single genes demonstrates the need for finding germplasm with multigenic resistance to the aphid. This study was conducted to map quantitative trait loci (QTL) for aphid resistance in PI 567324. We identified two major QTL (QTL_13_1 and QTL_13_2) for aphid resistance on soybean chromosome 13 using 184 recombinant inbred lines from a ‘Wyandot'' × PI 567324 cross. QTL_13_1 was located close to the previously reported Rag2 gene locus, and QTL_13_2 was close to the rag4 locus. A minor QTL (QTL_6_1) was also detected on chromosome 6, where no gene for soybean aphid resistance has been reported so far. These results indicate that PI 567324 possesses oligogenic resistance to the soybean aphid. The molecular markers closely linked to the QTL reported here will be useful for development of cultivars with oligogenic resistance that are expected to provide broader and more durable resistance against soybean aphids compared with cultivars with monogenic resistance.     

Field Evaluations of Augmentative Releases of Delphastus catalinae (Horn) (Coleoptera: Coccinellidae) for Suppression of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) Infesting Cotton

In 1992 and 1993, field evaluations were conducted to determine the efficacy of Delphastus catalinae (Horn) releases for the suppression of Bemisia argentifolii Bellows & Perring infesting cotton in the Imperial Valley of California. Augmentative releases of adult beetles, totaling 3.5 and 5.5 beetles per plant for 1992 and 1993, respectively, were made into four 0.2-hectare cotton plots and four exclusion cages covering 40 cotton plants. Equal numbers of field plots and cages served as controls for the D. catalinae releases. Open field evaluations revealed no significant difference in the whitefly densities between the release and the nonrelease fields. In addition, no differences in plant growth measures were detected in the year that these data were collected. Releases of D. catalinae into whitefly exclusion cages resulted in a 55% and a 67% decrease in whitefly densities in 1992 and 1993, respectively. Observational data suggested that intraguild predation on D. catalinae by the existing predator fauna may have limited the potential for D. catalinae to provide biological whitefly control in open field plots relative to the levels observed within the cages. Releases of D. catalinae did not adversely affect population densities of indigenous parasitoids, suggesting an absence of statistically significant, antagonistic predator–parasitoid interactions.