摘要:

Sterile, diploid males occur in many Hymenoptera and result from homozygosity at the sex locus. Multiple alleles exist at this locus so that diploid male production is inversely proportional to the number of alleles in a population. Allelic diversity can be maintained by a single, large population or via multiple, inbred lines. Simple calculations show that small numbers of inbred lines can maintain surprisingly high allelic diversity. Two-allele lines with ≥10 diploids per generation are unlikely to go extinct and may reduce culture effort, as well as being less affected than a large population by population crashes. However, the choice between a single, large population and multiple lines is affected by the biological attributes of a given host-parasitoid system. If resources permit a combination of both methods, this may be the best solution.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1213

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Implementation of augmentative biological control is often hindered by the inability to obtain accurate information on natural enemy release rates that will ultimately yield a salable crop within economic constraints. The purpose of this study was to develop and evaluate a computer model that attempts to predict augmentative releases of the parasitoidDiglyphus begini(Ashmead) (Hymenoptera: Eulophidae) to use for biological control against the serpentine leafminerLiriomyza trifolii(Burgess) (Diptera: Agromyzidae) infesting greenhouse-grown cut chrysanthemums. The model attempts to determine the appropriate release rate necessary to reduce leafminer densities below 1 larvae per 1,000 chrysanthemum leaves within 40 d after planting, after which time aesthetically important foliage forms on chrysanthemums. In the construction of this deterministic model, three simplifying assumptions have been made: (1) there is no insect movement between the greenhouse and outside, (2) greenhouse temperatures are a constant 27°C, and (3) the greenhouse represents a homogeneous environment. Model simulations indicated that successful biological control was unlikely when parasitoid releases are initiated later than 14 d after planting regardless of the release rate. The simulations also demonstrated thatD. beginirelease rates are not linearly related toL. trifoliidensities, and that a parasitoid release strategy is not simply the determination of a proper wasp/leafminer ratio. Validation studies of the model's predictions provided mixed results. Following the release rates generated by the model,L. trifoliilarval densities were not significantly greater than I per 1,000 leaves 40 d after planting. However, the model did not always track the succession and magnitude of leafminer population fluctuations with statistical accuracy. Two factors probably contributed to these errors in prediction: (1) the assumptions inherent to the model were not met during the validation trials, and (2) the leafminer subroutine of the model could not accurately predictL. trifoliidensities in the absence ofD. begini. In spite of these errors, leafminer damage to the harvested foliage was significantly lower in the treatments receivingD. beginireleases than in the control treatments. In addition, when the model was tested in a commercial cut chrysanthemum greenhouse,L. trifoliiwas successfully controlled by releases ofD. begini, resulting in the production and harvest of a salable cut chrysanthemum crop without the use of any pesticides. Finally, postvalidation reconstruction of the model, to include temperature-dependent variation in life history parameters, increased the predictive power of the model.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1217

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Since 1980,>16 million parasites ofHypera postica(Gyllenhal) were distributed across the United States as part of the Alfalfa Weevil Biological Control Program. Two species of internal parasites, one of the larval stage,Bathyplectes anurus(Thomson) and one of the adult stage,Microctonus aethiopoides(Loan), were released in the largest numbers. A detection survey conducted by the USDA, Animal and Plant Health Inspection Service, found that a second larval parasite,Bathyplectes curculionis(Thomson), had already spread throughout alfalfa-growing areas in the United States. Later, an establishment survey successfully recovered parasites in nearly half of the>700 counties where releases were made. Results from an evaluation survey indicated that the number of alfalfa weevil parasite species collected in surveyed fields in Iowa, Missouri, and Nebraska more then doubled from 1.3 to 3.0. Parasitism rates also increased in these states, whereas insecticide usage declined. However,<3% of the 180 alfalfa fields sampled during the 8 yr evaluation survey reached the economic injury level. BothB. anurus and B. curculionisexhibited differential success when parasitizing two United States strains (eastern and western) of the alfalfa weevil. These two species parasitized an average of 21% of the larvae collected in survey samples.M. aethiopoidescould possibly be an important method for keepingH. posticapopulations below economic injury levels. A delayed densitydependent relationship between this species and its host was demonstrated in three midwestern fields sampled for seven consecutive years. Before the first cutting of alfalfa,M. aethiopoideskilled an average of 26% of adult weevils in the four areas surveyed in the eastern United States. A fungal disease,Zoopthora phytonomi(Arthur), ofH. posticawas detected in the majority of fields in our evaluation survey; this too may be a method for reducing weevil populations.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1234

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Field studies were conducted in Virginia cornfields from 1989 to 1991 to evaluate a preplant method for detecting damage to germinating corn seeds by multiple species of insect pests, including seedcorn maggots,Delia platura(Meigen); several species of wireworms in the generaMelanotus, Conoderus, andAeolus; and several species of white grubs in the generaPopillia, Cyclocephala, Cotinis, andMaladera. The method used consisted of evaluating feeding damage to com seeds in wire-mesh traps (i.e., baited wire traps) that were buried in cornfields for ≍2 wk before planting. In the 1989 study conducted in a cornfield with a large infestation of wireworms, a significantly greater proportion of com seeds exhibited feeding damage in the baited wire traps (38.3%) compared with corn seeds planted by hand at conventional plant spacings (i.e., simulated commercial plantings) (31.5%). Further evaluation in 47 cornfields in 1990 and 1991 revealed no significant difference between the proportion of damaged corn seeds in the baited wire traps (2.7%) and simulated commercial plantings (2.0%). A Significantly greater proportion of com seeds exhibited feeding damage in the commercial plantings (5.4%) compared with the baited wire traps; however, mean stand loss associated with insect feeding in the commercial plantings was only 0.4%, which was substantially less than the proportion of damaged com seeds in the haited wire traps. Significant linear regressions were obtained between the proportion of damaged seeds in the baited wire traps and the proportion of damaged seeds in the simulated commercial plantings, commercial plantings, and proportion of stand loss in the commercial plantings. However, the lack of economic stand loss in the commercial plantings and low regression coefficient of determination precluded the development of a baited wire trap damage threshold to predict stand loss in fields subsequently planted with corn.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1251

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Transmission of Potato Virus Y (PVY) by several aphid vectors was studied under laboratory and greenhouse conditions to determine vector propensity on sweet pepper (Capsicum annumL.) plants. Laboratory experiments were conducted with three PVY strains: pepper-PVY pathotypeφ (PVYφ) and potato-PVY (ordinary strain, PVY∘, and necrotic-type strain, PVYN). Pepper (‘Yolo Wonder’), tobacco (Nicotiana tabacumL., ‘xhanthi nc’), and potato (Solanum tuberosumL., ‘Bintje’) were used as virus sources or test plants, or both. Results showed that both pepper-PVY and potato-PVY strains were transmissible byMyzus persicaeSulzer to pepper plants, although potato-PVY∘ and – PVYNare less efficiently transmitted than PVY∘. Transmission tests between different species of aphids using PVY∘-infected pepper and tobacco as source plants indicated thatM. persicaewas the most efficient vector, followed byAphis gossypiiGlover andAcyrthosiphon pisumHarris.Aphis fabaeScopoli also was capable of transmitting PVY∘, but with much less efficiency. Greenhouse experiments designed to evaluate the dispersion (secondary spread) of PVY by alatae aphids indicated thatM. persicaetransmitted the virus at the highest rate.Aphis fabae and Aphis gossypiialso were able to spread PVY efficiently under test conditions. Previous works indicated that non-colonizer species, principally in the genusAphis, have much higher alate activity in open field conditions (higher landing rate) thanM. persicae. Therefore, much of the natural spread of virus may be by species that are not commonly found feeding on pepper crops.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1260

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Greenhouse studies were conducted to determine the role ofThrips tabaciLindeman injury to onion,Allium cepaL., in the invasion of the fungal pathogenAlternaria porri(Ellis) and the subsequent development of the disease purple blotch. Individually caged onions were infested with 25 thrips per plant and inoculated 20 d later withA. porri(1,000 spores per ml of H2O). Onions were rated 6 and 7 d after inoculation. Plants infested with thrips and inoculated withA. porrideveloped more and larger lesions that coalesced as the plant matured. Older leaves were more susceptible toA. porriinfection in the absence of thrips injury. Purple blotch infection shifted to younger leaves as a result of thrips injury to onion, and more tissue was killed by thrips in the presence of purple blotch. Plant growth was negatively correlated with thrips feeding injury. Scanning electron microscopy was used to determine morphological changes in leaf tissue resulting from thrips feeding injury and the development of purple blotch. In the absence of thrips injury,A. porrienters onion leaf tissue through stomates and directly through the epidermal cell layer. When both thrips injury and purple blotch are present, leaf tissue is extremely necrotic andA. porriappears to use areas of insect damage as alternative penetration sites. Thus, the feeding wounds caused by thrips enhance entry and development of the disease by providing alternative penetration sites forA. porri.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1266

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Correlations between population levels of pink sugarcane mealybug,Saccharicoccus sacchari(Cockerell), on sugarcane and the chemical status and texture of soils, location of sites, and date of previous harvest were examined in southern Queensland. In 1989, calcium, copper, exchangeable aluminum, iron, magnesium, manganese, sodium, total nitrogen, zinc, and pH were correlated with numbers ofS. sacchari. In 1990, none of the chemical factors was Simply correlated with numbers ofS. sacchari, although a quadratic regression of zinc levels accounted for 31% of the variation in numbers ofS. sacchari. The data suggest that numbers of S. sacchari are lower in fields with either low or high zinc levels. Soil texture components (clay, sand, silt) were not simply correlated with numbers ofS. sacchariin either year. There was a significant quadratic regression with sand content in 1989, indicating higher numbers ofS. sacchariwith soils containing 70% sand. Distance of sites from the coast and date of previous harvest were not correlated with numbers ofS. sacchari.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1278

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

The effect of pinewood nematode,Bursaphelenchus xylophilus(Steiner&Buhrer) Nickle, infection on the preformed defensive response of loblolly pines,Pinus taedaL., near Pineville, LA, was quantified from 1987 through 1990. Each year, trees were inoculated with ≍50,000 pinewood nematodes in all life stages. An equal number of control trees were inoculated with sterile, distilled water. Oleoresin flowwas monitored on each tree on a monthly basis from four wounds, equally spaced around the bole and located ≍3 m above ground level in 1987 and 1–2 m above ground level during subsequent years. Sustained significant reductions in oleoresin flow were noted in the nematode-inoculated trees for 6 mo after inoculation in 1988and for 5 mo after inoculation in 1990.A significant reduction was noted for one sampling period during 1989, 3 mo after inoculation. No differences were noted in 1987. Oleoresin flow reduction on nematode-inoculated trees was influenced by seasonal changes in oleoresin flow and the timing of soil moisture deficits.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1285

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

The influence of leaf phenology on host discrimination byPhytomyza ilicicolaLoew was explored in the laboratory by examining the influences of leaf age-shoot position on adult feeding and oviposition and leaf age only (independent of relative leaf position on expanding shoots) on adult feeding. The relationship between adult feeding and shoot phenology among trees was also examined in 10 American hollies,Ilex opaca Aiton, growing under natural forested conditions. Three age-position classes of leaves were recognized on new growth in the spring: young folded leaves at shoot tips, expanding leaves at midshoot, and fuIly expanded hardening leaves at the base of shoots. For leaf age-position, feeding by adultP. ilicicolawas similar on expanding leaves and fully expanded leaves and 3.6 times greater on shoot tip leaves than on expanding and fully expanded leaves. For leaf age independent of position, feeding by adultP. ilicicolawas 9 times greater on expanding leaves than on fully expanded leaves and 20.7 and 2.2 times greater, respectively, on shoot tip leaves than on fully expanded leaves and expanding leaves. Oviposition was independent of leaf age and position on new shoots. There was no relationship between tree phenology and intensity of feeding under natural conditions.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1294

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Previous studies concluded that species in the coccinellid genusStethorusWeise, although obligate predators of tetranychid mites, exhibit a strong numerical response only to high population densities of their prey. The study reported here was conducted to test the hypothesis that in western Washington red raspberries,Stethorus punctum picipesCasey is capable of detecting and attacking spider mite populations of very low density which are distributed in small, widely scattered patches during the early part of the growing season. In addition to using conventional leaf sampling methods,S. p. picipesinteractions with prey were examined by observing their response to prey patches introduced into the field from laboratory cultures. Our results indicate thatS. p. picipesis active at low prey densities, although undetected by conventional sampling methods, and is capable of locating rare, small prey patches. This finding suggests that dispersal and searching ability, rather than numerical response are the key components of this preypredator association.

ISSN:1754-5692    

DOI:10.1093/ee/22.6.1302

出版商:Oxford University Press    

年代:1993

数据来源: OUP