摘要:

The cecidomyiid midgeRhopalomyta californiaFelt is native to California where its larvae develop in terminal galls onBaccharis pilularisDC. Galls are usually multichambered and can contain>50 larvae per gall (one larva per chamber). Regression analyses involving>3,500 galls collected on 21 sample dates at two field sites in northern California revealed that average percentage of survival (larva to adult) ofR. californiawas either independent of, or directly related to, gall size (chambers per gall). No inverse density dependence was detected, suggesting that any intraspecific competition that may have occurred in larger galls did not reduce midge survival. This was confirmed in laboratory studies. The apparent inability of the midge's primary parasites to fully exploit host larvae in larger galls also may enhance midge survival in these galls. Under laboratory conditions, however, the mean number of eggs per female was significantly reduced in females that developed in larger galls, suggesting that intraspecific competition among larvae occurred. These patterns, if observed onB. halimifoliaL., could influence the effectiveness ofR. californicaas a biological-control agent for this weed in Australia and elsewhere. It is suggested that response to intraspecific competition be included in preintroductory evaluation of candidate agents in biological control of weeds.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1558

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The dispersal and survival of neonate diamondback moth larvae,Plutella xylostella(L.), were measured on normal bloom susceptible ‘Round-Up’ cabbage and a resistant genotype descended from glossy cauliflower, PI 234599. During the first 24 h after hatching, neonateP. xylostelladispersed more rapidly and initiated fewer mines on the resistant glossy 2518 than on ‘Round-Up’. Also, a greater proportion of neonates were found dead on 2518 than on ‘Round-Up’. Individual neonates had significantly higher movement rates on three glossy resistant genotypes ofBrassica oleraceathan on two normal bloom types. Movement rates were negatively correlated with percentage of larvae surviving to fourth instar. Removal of leaf epicuticular waxes with dichloromethane or disruption of the wax morphology eliminated the difference in movement rate on ‘Round-Up’ and 8329, a glossy cabbage descended from PI 234599. Headspace vapor of 8329 or ‘Round-Up’ plants did not affect movement rates of neonateP. xylostella. The results indicate that wax morphology is of primary importance in producing increased larval movement rates on glossy resistant lines. Wax chemistry may also contribute to the effect. Neonate nonpreference for leaf wax characteristics is proposed as the mechanism of resistance toP. xylastellain glossyB. oleracea.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1566

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The effect of isofenphos (Oftanol) on nontarget invertebrates in turfgrass was determined by comparing population dynamics of eight taxa sampled from treated versus untreated halves of home lawns. Lawns were treated in late summer 1980 or spring 1981. Populations of predacious Acari, Collembola, Diplopoda, Diplura, and Staphylinidae were reduced in treated areas. Higher populations of oribatid Acari and Enchytraeidae were found in treated areas. The time required for recovery ranged from several weeks to 8–10 mo depending on the taxa; edaphic and predacious groups were affected the longest.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1572

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

A simulation model was constructed to examine the effects of intraplant spatial dynamics of the lepidopteran pest complex of cabbage on direct damage to the marketable parts of the plant. Diurnal fluctuations in microclimate for different parts of the crop canopy were simulated with sine functions. Larval development rates for each species were simulated with logistic functions of temperature, the development process with time-varying distributed delays, and feeding rates with exponential functions of temperature and larval age. Larval transition probabilities within the crop canopy were modeled with either constants or definite integrals of the Beta probability density function, the shape parameters of which were modeled as functions of temperature. The model provided a good fit to data on changes in intraplant distribution of these larvae and intraplant distribution of feeding damage. Evaluation of model predictions suggests that a threshold population density used for management decisions should not be static, but should be a complex function of species, larval age distribution, and forecast temperatures. A model like the one presented here could serve as that complex function.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1578

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The ovipositional status of field populations of adult stable flies,Stomoxys calcitrans(L.), in cattle feedlots was investigated for 3 yr in southeast Nebraska. The proportions of female flies in each of three ovipositional stages (nulliparous, uniparous, and biparous) collected by two sampling methods (a stanchioned-calf technique and Alsynite fiberglass traps) at three times of day at two cattle feedlots were compared. In 2 of the 3 yr of the study, location (Feedlots A, B, or C), time of sampling (0800, 1100, and 1400 hours), and method of collection did not affect significantly the proportions of female stable flies in each ovipositional stage. During the 3 yr of the study, nulliparity was the predominant ovipositional stage. At the time of population peaks of adult stable flies, the majority of female stable flies were nulliparous, which indicates that the population peaks are caused by young flies that had recently emerged. More than 97.0% of the female flies collected during this study had immature eggs. We concluded that both methods sampled the same population of female stable flies: each method has strengths for different types of ecological studies. Also, we feel that increasing stable fly populations at any feedlot develop on site and are not a result of immigration. Furthermore, at beef cattle feedlots, most adult female stable flies do not live much beyond one egg cycle.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1597

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Distribution characteristics of the western flower thrips,Frankliniella occidentalis(Pergande), and the predatory miteAmblyseius cucumeris(Oudemans) were studied on greenhouse cucumber and used in developing presence–absence sampling procedures. The variance-mean relationship was described by Taylor's power law and resulted in aggregation indices on middle leaves of 1.62 for thrips larvae and 1.31 for thrips adults andA. cucumeris. Tables are presented for estimating population density from percentage of leaves infested and for determining sample size required at different population densities and precision levels. Thrips density correlated with leaf damage but not with fruit damage.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1605

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The alfalfa seed chalcid,Bruchophagus roddi(Gussakovsky), is the most destructive insect to alfalfa,Medicago sativaL., seed. Because chemicals are ineffective in its control, plant resistance offers the most viable method of reducing seed losses. The objective of our study was to compare pod-wall characteristics with seed damage and resistance to the alfalfa seed chalcid in eightMedicagospecies and three interspecific hybrids. The percentage of chalcid-damaged seed, based on seed numbers, averaged 0.0% for annual species, 18.4% for perennial glandular-haired species, and 20.4% for perennial control cultivars. The percentage of other seed losses averaged 8.4% for perennial control cultivars, 21.3% for annual species, and 35.5% for perennial glandular-haired species. Pod-wall thickness averaged: perennial glandular-haired species, 131.9μm; annual species, 139.4μm; and perennial control cultivars, 144.0 μm. Increased pod-wall thickness reduced other seed losses not attributed to the chalcid. Phenotypic variation in pod-wall thickness suggests that selection for this trait should be effective, assuming there is significant heritable variation. Our findings suggest also that pod-wall lignification may reduce seed losses due to chalcid damage. The highest levels of resistance to the alfalfa seed chalcid were found in the annual species, which also had highly lignified pod-walls. The annual species, however, are cross-incompatible withM. sativa. Thus, breeding for increased pod-wall lignification may reduce seed losses due to damage by the chalcid, if the mechanisms that control lignin production and accumulation are heritable and in cross-compatibleMedicagogenotypes.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1614

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

‘Deglet Noor’ date gardens were subjected to various degrees of sanitation of damaged dates to observe effects on infestation of a carob moth,Ectomyelois ceratoniae(Zeller), raisin moth,Cadra figulilella(Gregson), four species of nitidulid beetles, and fungal infection. In a year of above average rainfall, 1984, infestation by carob math, raisin moth, and nitidulid beetles was significantly reduced at harvest (P<0.05) in areas sanitized by the weekly removal of damaged dates from the ground. Fallen dates consisted of “Junedrop” and khalal stage dates, many of which had been infected by fungi (chieflyAspergillusandAlternariaspp.) as a result of rain. These provided a substrate conducive for the buildup of insect populations in July and August. However, in a year of no summer rainfall and above-average summer temperatures (1985), June-drop dates became completely desiccated in the palms and on the ground, and fungal infection of khalal stage dates was inhibited. Consequently, populations ofE. ceratoniae, raisin moth, and nitidulid beetle were greatly suppressed by the lack of suitable substrates and no benefit by sanitation was indicated.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1618

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

A pest control decision rule consisting of an action threshold and a sampling protocol was developed and evaluated for first-generation spotted tentiform leafminer,Phyllonorycter blancardella(F.). An action threshold of two eggs per leaf was chosen based on the criterion of preventing more than one first-generation mine per leaf. Two sequential classification sampling plans for first-generation eggs were developed, one based on variable intensity sampling and the other on the use of confidence intervals for stop limits. Both plans made use of the nested variance structure of leafminer egg counts and variance-mean models fit to estimated variance components. Performance of the two sequential procedures was studied using simulation and judged to be very similar. Use of either sampling plan required approximately 10–20 min. Over a 4-yr period, 87% of sampled orchards in western New York had leafminer populations that were below the threshold of two eggs per leaf. During this period, use of sample information to schedule insecticide treatments resulted in only one instance when a treatment may have been required and was not called for (n= 79). Widespread use of the decision rule would result in significant reductions in pesticide use with no attendant increase in risk to growers.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1624

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Wing-type pheromone traps were used to monitor flight activity of the sunflower moth,Homoeosoma electellum(Hulst), in Kansas during 1986 to 1988. Traps were maintained at Belleville, Hays, Hesston, Hutchinson, and Manhattan in sunflower (Helianthus annuusL.) plots planted at three dates from mid-May to mid-July. Traps were set in the fields before blooming of the crop and monitored until plant maturity. Moths were trapped from mid- to late July until the end of August in 1986 and late September in 1987. The maximum number of moths was trapped from mid-July to mid-August at most locations in both years. Very few moths were caught during 1988, when adults were in the area from late July until the second week of September. Number of larvae per head was higher in plots blooming around peak moth appearance at most places in all three years. Number of larvae per head were lower in plots blooming after mid-August, when fewer moths were also trapped. The pheromone traps were efficient tools to detect the presence of the pest in the field. A significant relationship was found between number of moths in traps and larvae per head during 1986 and 1987 but not in 1988.

ISSN:1754-5692    

DOI:10.1093/ee/19.5.1639

出版商:Oxford University Press    

年代:1990

数据来源: OUP