摘要:

Sequential sampling plans are appealing because fewer observations are needed than those needed for fixed sampling plans to make a terminating decision when insect populations are sparse or abundant. Wald's Sequential Probability Ratio Test (SPRT) commonly has been used in monitoring insect populations and damages from these populations. At times, particularly for moderate infestations, the SPRT with its parallel boundaries takes longer than a comparable fixed-sample-size method to make a terminating decision. An alternative sequential testing procedure called the 2-SPRT for the negative-binomial parameter P is demonstrated. The value of the exponent k is assumed to be known. In this procedure two one-sided SPRTs are performed simultaneously, which results in the convergent boundary lines. The average number of observations needed for the terminating decision for medium infestations (i.e., for P1

DOI:10.1093/ee/22.2.346

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Recognizing the existence and importance of intra- and interspecific competition in natural populations of insect herbivores remains problematical. We performed field-cage experiments to detect the presence of both intra- and interspecific competition among adults of two common, grass-feeding grasshoppers,Ageneotettix deorum(Scudder) andAmphitornus coloradus(Thomas). Based on increased mortality and lowered fecundity at higher densities, strong evidence for intraspecific competition exists for both species. Interspecific competition was weaker than intraspecific competition in this study. When interspecific competition existed, it was asymmetric in its effect, with the larger species (A. coloradus) negatively impacting the smaller one (A. deorum). Although there was little evidence for interspecific effects on mortality, egg production was impacted in a size-dependent, asymmetric manner between the two species. Significant density dependent depression of available food was observed forA. coloradus, the larger species. Experiments were nm at high densities (10–30 individuals per square meter), levels only irregularly reached under natural conditions (either in sporadic patches or overall about every 10–12 yr). Because naturally occurring densities are typically below the competitive threshold, interspecific competition between these two species may occur only intermittently. Other forces may greatly impact adult mortality at this site, including predation.

DOI:10.1093/ee/22.2.352

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

A survey of the margarodidsEumargarodes laingiJakubski andPromargarodesspp. in sugarcane was carried out at Bundaberg, southeastern Queensland, Australia.E. laingicyst numbers were influenced by soil type; Promargarodes spp. numbers did not differ between soil types, but there were differences between cultivars. There were moreE. laingiandPromargarodesspp. cysts in older crops. The number of times the previous fallow was plowed and rotary hoed influencedE. lainginumbers, but notPromargarodesspp. numbers. There were fewerE. laingicysts after a long fallow, but crop rotations did not affectE. lainginumbers. There were trends to lowerPromargarodesspp. numbers after a long fallow or a sugarcane-rockmelon rotation. Fields treated with chlorpyrifos (emulsifiable concentrate) had lower numbers ofE. laingithan those treated with controlled release chlorpyrifos;Promargarodesspp. numbers were not influenced by insecticide applications. Soil pH and electrical conductivity, ripping during fallow, type of irrigation, and nematicides used did not affect numbers ofE. laingiorPromargarodesspp.

DOI:10.1093/ee/22.2.362

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Quantification of dispersal distances is critical in modelling the potential invasion ofCochliomyia hominivorax(Coquerel) into Australia. This study draws together a number of trials on dispersal of screwworm fly. While different in many aspects, data proved to be of a similar distributional shape, well described by the Cauchy distribution. Population dispersal distances were shown to depend on sex (females disperse farther than males), and environmental favorability as measured by habitat and availability of hosts. Under favorable conditions, the majority of female screwworm flies move<3 km, but in unfavorable habitats, movement can be 8 times greater.

DOI:10.1093/ee/22.2.368

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

The sweetpotato whitefly,Bemisia tabaci(Gennadius), attacking peanut,Arachis hypogaeaL., in Georgia was identified as Strain B. Based on the Brooks-Dyar rule for geometric growth, four nymphal instars occurred on peanut. Average length and width (μm), respectively, for the instars were (mean ± SE): first, 207.8 ± 5.4, 120.9 ± 4.4; second, 314.9 ± 8.8, 194.0 ± 6.4; third, 442.6 ± 11.2,289.1 ± 8.0; and fourth, 619.3 ± 9.2, 428.7 ± 4.4. Few immatures were found on the terminal and second leaf of a lateral branch. They were most abundant on leaves 3, 4, and 5, and then numbers declined with an increase in leaf age. Immatures occurred on both upper and lower leaf surfaces. Immatures were equally distributed among the tetrafoliates of a peanut leaf, but their location on upper versus lower leaf surface varied over time. Yellow sticky traps placed in a horizontal position at ground level or at canopy level and with the sticky surface upward were most effective in capture of adult sweetpotato whiteflies. The number of immatures on peanut leaves was only weakly related to the number of adults captured in sticky traps 1 wk earlier.

DOI:10.1093/ee/22.2.375

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

A 7-yr study on field plots in Lleida, northeastern Spain, was carried out to determine the factors that playa major role in the population dynamics of cereal aphids in winter under Mediterranean conditions. Plots were monitored at 7–10-d intervals from crop emergence until the first fortnight in April using a D-vac vacuum net set. Several weather and host plant parameters were related to the following aphid population changes: (1) seasonal net rates of aphid increase (from the first sampling in October or November to 31 March), (2) net rates of increase, and (3) k mortality values between consecutive samplings. Population dynamics ofRhopalosiphum padi(L.) andSitobion avenae(F.), the species found most frequently, were affected, not only by low temperatures causing aphid mortality but also hy other factors. Dry and cold weather, through the effect they have on host plant phenology and quality, reduce aphid developmental rates. Winter minimum temperatures and rainfall, the latter by its effect on host plants, seem to be the major weather parameters to consider to forecast aphid population levels at the beginning of spring.

DOI:10.1093/ee/22.2.381

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

To assess whether plant phenology may affect potential for host shifts,S. altissimaandS. giganteawere monitored in the field in Minnesota (both host races), in Pennsylvania (S. altissima, sole host), and in a Pennsylvania common garden of both host plants from both sites. Plant height was measured every other day, and growth rates were calculated through the oviposition period in the field and season-long in the common garden. Greenhouse-grownS. giganteafrom both locations were subjected to oviposition byMinnesota Eurostato compare galling susceptibility. Minnesota hosts had more comparable growth rates and more intraspecific variability than the same species in Pennsylvania.S. giganteagrowth peaked earlier and fell more rapidly than that ofS. altissimafor all populations, suggesting an earlier, narrower window of host suitability. PennsylvaniaS. giganteawill support gall formation, but ramet growth rate was significantly less than that of MinnesotaS. giganteaunder greenhouse conditions, and MinnesotaEurostastrongly preferred Minnesota ramets to those from Pennsylvania. Variations in daily growth rate fluctuations between species may confoundEurosta'sdetection of suitable hosts. These results indicate a higher probability of a host shift occurring in Minnesota than in Pennsylvania and may indicate why colonization ofS. giganteahas not occurred in Pennsylvania.

DOI:10.1093/ee/22.2.388

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Feeding and oviposition preferences of adult cottonwood leaf beetles,Chrysomela scriptaF., vary among leaf age classes andPopulusclones. Phenolic glycoside profiles of different age classes from sevenPopulus, representing a range of preferences, were examined for salicin, salicortin, and tremulacin composition and concentration among leaf age classes, as measured by leaf plastochron index (LPI). For each clone, extracts from the most preferred leaf age class for both behaviors (LPI 3) and from a nonpreferred class (LPI 12) were examined. Significant differences in the concentrations of these glycosides were found both between leaf age classes and among clones. The LPI 12 leaves contained lower concentrations of all three glycosides than the LPI 3 leaves. Comparisons were made between feeding and oviposition preferences and glycoside content. These suggest that salicin and salicortin content do not negatively influence host selection but that tremulacin may negatively influence such behavior.

DOI:10.1093/ee/22.2.397

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Mediterranean fruit fly,Ceratitis captitata(Wiedemann), was monitored with male lure trap collections and periodic collections of ripe fruits on the island of Kauai to determine its temporal appearance and distribution patterns. Results showed marked temporal differences in peak trap catches of the fly in lowland areas compared with upland areas. Flies were caught in two upland locations compared with catches in six lowland locations. Strawberry guava,Psidium cattleianumSabine, and common guava,Psidium guajavaL., form a discontinuous belt of plants around Kauai Infestation of this fruit byC. capitatawas nearly absent in wet areas and consistent but variable in dry areas. The seasonal appearance ofC. capitatain traps in Kokee and Polihale coincided with their emergence from collected fruits. The mean infestation rate ofC. capitatain guava was 0.43 ± 0.27 (mean ± SEM) per kg of fruit compared with 37.5 ± 15.3 forBactrocera dorsalis(Hendel), Infestation of all fruits collected byB. dorsaliswas widespread in all areas when these plants produced ripe fruits. Utilization of all fruits byC. capitatawas very limited in comparison with the distribution and abundance of host plants.

DOI:10.1093/ee/22.2.404

出版商:Oxford University Press    

年代:1993

数据来源: OUP

摘要:

Extrafloral nectar, a solution of both sugars and amino acids that is produced by plants on stems and leaves, attracts ants that often protect the plants from potential herbivores. To understand better the ecological significance of variability among plants in nectar chemistry, the effectiveness of ant attraction by different extrafloral nectars was compared for nectar mimics that varied in either amino acid or sugar content. Workers of the fire antsSolenopsis invictaBuren andS. geminata(F.) were fed on artificial nectaries containing mimics of pre- and postdefoliation nectars ofImpatiens sultani, which differed in amino acid content. Workers of the two fire ant species also fed from artificial nectaries containing mimics ofPassiflora ambigua,P. talamancensis, andP. quadrangularis, which varied in sugar composition.S. geminataworkers preferred the more amino acid-rich postdefoliation mimic over the predefoliation mimic.S. invictadid not discriminate between the two nectars, demonstrating that richer amino acid solutions are not more attractive to all ants. In the sugar experiments, both species of ants preferred the nectar ofP. ambiguaover those of the other twoPassifloraspecies. The nectar ofP. ambiguahad the lowest total sugar concentration and the lowest calorie content, indicating that ants do not necessarily maximize sugar energy intake as they forage. The behavior ofS. geminataandS. invictashows that both amino acid and sugar content can affect ant recruitment to plants and that differences in levels of recruitment cannot be predicted accurately based on simple assumptions of nutrient maximization or energy content.

DOI:10.1093/ee/22.2.411

出版商:Oxford University Press    

年代:1993

数据来源: OUP