摘要:

Western tent caterpillar,Malacosoma californicum pluviale(Dyar), larvae were treated with nuclear polyhedrosis virus (NPV) in the laboratory to assess whether the presence of virus could potentially explain reduced fecundity observed in declining field populations of the host. In 1992, male and female pupal weights and female fecundity were reduced in survivors of virus treatment. In 1993, using the same viral dosage on individuals from a different population resulted in reduced pupal weight (and fecundity) in females only. Strong family effects were also detected for male and female pupal weights and fecundity in both years. Results from 1992 data showed a significant effect of virus treatment on fecundity when variability related to pupal weight was removed, suggesting that NPV could directly affect egg production. This pattern was not observed in 1993. These experiments suggest that NPV has the potential to cause reduced fecundity in field populations of the western tent caterpillar.

DOI:10.1093/ee/23.4.864

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

In a previous study, ants had a significant effect on gypsy moth,Lymantria dispar(L.), numbers in a forest where the trees were only about 3 m high. The present study was carried out similarly, but trees were about 20 m high. In some plots, ant numbers were suppressed by a combination of barriers and poison baits. In other plots, 24% sucrose sprays were applied with a back-pack mist blower in an attempt to increase ant abundance, but no increases occurred. There was a nonsignificant trend for caterpillar numbers to be higher in the plots where ants were suppressed, and gypsy moth larval counts on leaves of trees were negatively correlated with ant counts on leaves. Thus, there is evidence that ants have an effect on gypsy moth caterpillars in mature forests as well as in young ones.

DOI:10.1093/ee/23.4.870

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Insect pollination of commercial annonaceous crops is variable among localities and poorly understood. To gain basic information for use in pollinator management programs, we studied the nitidulids that pollinate commercially grown sugar apples (Annona squamosaL.) and atemoyas (A. squamosa X A. cherimolaP. Miller) in Florida. Only flowers visited by nitidulids set fruit. We found nine species of nitidulid flower visitors, seven of which pollinated.Carpophilus mutilatusErichson was the most important pollinator in terms of efficacy and abundance, followed byC. fumatusBoheman andHaptoncus luteolus(Erichson). TheAnnonaflowers, which are protogynous, are entered by the beetles usually during the female phase. Peak entry into atemoya flowers occurs in the morning (0700–0900 EST) and into sugar apple flowers both in morning (0700–1100) and evening (1700–2100). The beetles remain inside up to 22 h, until the flowers senesce and the stamens fall. In 1989, natural fruit set ranged from 0–29% of sampled flowers per day in atemoya groves and from 0–10% of flowers per day in sugar apples. Percentage of fruit set is correlated with numbers of nitidulids in the flowers.

DOI:10.1093/ee/23.4.878

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

The oviposition behavior ofDisonycha pluriligatain relation to food plants for larvae was considered a critical link between generations in the life history of this beetle relative to its population dynamics. Therefore, we undertook studies to clarify female behavior before and during oviposition and the consequences for larval establishment on the host plant,Salix exigua.Field studies showed that females dig depressions in the soil, into which they lay a clutch of eggs, with some clutches covered with soil and others left uncovered. Therefore, first-instar larvae had to find host plants and started feeding low on the foliage. An experiment using caged adults on potted willows showed that females always feed and copulate before oviposition, and they lay eggs up to 15 cm away from a plant, which was the maximum radius available in the pots. In petri dishes, females oviposited in soil, on paper towel, and on bare plastic. Females demonstrated a relatively indiscriminate oviposition behavior, leaving larvae to forage independently for host plants. We hypothesize that this lack of linkage between ovipositional preference and larval performance places strong selective pressure on larvae to be relatively indiscriminate feeders, predisposing them to be generally able to eat any quality of leaves in a stand of willows and, as a consequence, to be damaging and eruptive in their population dynamics.

DOI:10.1093/ee/23.4.887

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Degree-day (DD) estimates based on different numbers of daily temperature readings recorded at regular intervals were analyzed for precision and bias. Given a temperature threshold below the daily minimum, one median standard deviation was 0.067 + 0.103, −0.043 (95% confidence limits) DD. Bias in the degree-day estimates was detected as a function of time of year, and the relative position of the threshold between the minimum and maximum temperatures, however, the bias was less than 0.030 + 0.00193 (SEM) DD per day. Hourly temperature data provided a better estimate of degree-days than mathematical functions fit to minimum and maximum temperature data. Use of mathematical functions results in function specific bias that changes with time of year. In those instances where the timing of phenological events has been based on a particular function, continued use of the function is necessary for consistent results.

DOI:10.1093/ee/23.4.893

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Populations of the cabbage seedpod weevil,Ceutorhynchus assimilis(Paykull), were sampled in Fayette, Haywood, Henry, and Lake counties in seven and eight commercial rapeseed,Brassica napusspp.oleiferaL., field sites in 1990 and 1991, respectively. The cabbage seedpod weevil was the most abundant (98.8%) of the eight curculionid species collected. AdultC. assimilispopulations were monitored weekly from 7 April to 4 June 1990 and from 10 April to 4 June 1991. During early season, overwinteringC. assimilisadult populations peaked on 27 April 1990 and 11 April 1991, respectively. Late in the season, adultC. assimilis(probable F1) populations peaked again on 4 June 1990 and 22 May 1991, respectively. Cabbage seedpod weevil populations were relatively low at sites in 1990; however, the total weevil population in Henry County was 79 times higher than that in Lake County in 1991. In the absence of commercial rapeseed fields, weevil densities in 1993 were 229 times greater on turnip,B. rapaL., in Henry County than in Lake County. A hypothesis for the higher weevil populations is that Henry County has more available alternate hosts and overwintering sites. Because rapeseed is new andC. assimilisis well adapted to this host, weevil infestations will likely increase and severely damage rapeseed stands as plantings increase in West Tennessee.

DOI:10.1093/ee/23.4.900

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Flowers of Japanese honeysuckle,Lonicera japonicaThunb., were found to support larval populations of tobacco budworm,Heliothis virescens(F.), and corn earworm,Helicoverpa zea(Boddie), in southwestern Georgia and northern Florida. However, larvae were not detected in samples taken during 1990 in southeastern Oklahoma and eastern Texas. This discovery constitutes a new host record for bothH. virescensandH. zea.Studies conducted at 10 different sites in Tift County, Georgia, during 1988–1990 revealed thatH. virescenspopulations peaked on Japanese honeysuckle during the F1 generation of April through May and again during August through September.H. zealarval populations occurred principally during August through September. Peak F1 larval populations ofH. virescenson Japanese honeysuckle occurred at the same time as those on crimson clover,Trifolium incarnatumL., and wild geranium,Geranium carolinianumL. BothH. virescensandH. zealarvae were capable of developing on Japanese honeysuckle flowers in the laboratory. Although survivorship was lower,H. virescensalso developed on Japanese honeysuckle leaves and berries.Cardiochiles nigricepsViereck was the principal species parasitizingH. virescens; parasitism ofH. zeawas negligible andMicroplitis croceipes(Cresson) was the only species detected.M. croceipeswas the primary parasitoid ofH. virescensandH. zealarvae collected from crimson clover. Results of this study indicate that Japanese honeysuckle is an important early season host ofH. virescensand an important late-season host for bothH. virescensandH. zeawhen overwintering populations are developing.

DOI:10.1093/ee/23.4.906

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

We developed a simulation model of monogyne red imported fire ant,Solenopsis invicta, populations that operates by competitive interactions of individual colony territories. This model describes six major aspects of colony lite history: nest founding, brood raiding, territory expansion, queen death, possible requeening, and colony death. Individual colony territories are represented by rectangles, whose sides change independently depending upon the presence and size of neighboring colonies. Growing colonies try to occupy free space, while retaining square territorial dimensions whenever possible. The growth of fire ant populations in the model compared well with available field data. The model predicted that competitive exclusion caused by territorial interactions should occur when areas reach 70–90% territory coverage. Several computer experiments were conducted with the model to examine the importance of colony growth rate, brood raiding activity, and other parameters on the relative success of sequentially founding colony cohorts. A 1-wk advantage in founding generally increased the long-term survival of young colonies by 40–80%. We also examined the factors affecting average coverage of an area by colony territories. Maximum coverage was achieved under a continuous influx of 50 queens/(ha·wk) or a single settlement of 1000 queens/ha; both values were much less than actual magnitudes of queen influx observed in the field.

DOI:10.1093/ee/23.4.912

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Results from three-choice and no-choice bioassays conducted under controlled conditions, and results from a field experiment indicated that adult white pine weevil,Pissodes strobi(Peck), collected from both Norway spruce,Picea abies(L.) Karst, and eastern white pine,Pinus strobusL., plantations, significantly preferred Norway spruce to eastern white pine and white spruce,Picea glauca(Moench) Voss, for feeding and oviposition activities. Weevil populations from Norway spruce and eastern white pine plantations responded similarly in a three-choice bioassay and in the field experiment, but in a no-choice bioassay weevils from the eastern white pine laid significantly more eggs and produced more feeding cavities compared with those from the Norway spruce. Results from the three-choice bioassay indicated that host interspecific discrimination by the weevil is more pronounced on spring than on late summer bark. Insects from the no-choice bioassay showed significantly greater feeding and ovipositional responses on Norway spruce than on the other two host-species in the spring. However, in the fall, differences were not significant.

DOI:10.1093/ee/23.4.923

出版商:Oxford University Press    

年代:1994

数据来源: OUP

摘要:

Per capita population growth rates (r) of the aphidsAphis gossypiiGlover on cucumber (Cucumis sativusL. ‘Vetomil’) andMyzus persicae(Sulzer) on pepper (Capsicum annuumL. ‘Midal’) were compared on plants provided varying concentrations of nitrogen (N) in nutrient solutions. ForA. gossypiion cucumber, treatments included a solution first at 90 then at 175 ppm N, a constant 175, and a constant 225 ppm N solution. The rate of population growth ofA. gossypiiwas Significantly lower on the 90–175 ppm N solution than on either the 175 or 225 ppm N solution, which were nearly equal. The mean time to first offspring was significantly longer for aphids on cucumber provided the 90–175 ppm N solution than on 175 ppm N. Higher fecundity was observed for aphids on plants provided 175 and 225 ppm N.A. gossypiisurvivorship was shorter in the 90–175 ppm N treatment than in the higher N treatments (x2= 6.7,P= 0.04). At the time aphids were placed on the plants, the percentage N in leaves was significantly lower in the 90–175 ppm N treatment than in the other two treatments (P<0.01).The solutions provided to pepper plants were a 60 ppm N solution in the vegetative, 90 in the early fruit, and 120 in the late fruit stage, a constant 120 ppm N and a constant 175 ppm N. Ther-values forM. persicaeranged from 0.31 to 0.36 and increased with N concentration (experiment 1,P= 0.05; experiment 2,P<0.02). The higherr-value for aphids in the 175 versus 120 ppm N in experiment 1 was caused in part by a significantly shorter time to production of first offspring (P<0.01). In experiment 2, the time to production of first offspring was the same in the 120- and 175-ppm N treatment, but higher fecundity was observed in the 175 ppm N treatment. Percentage foliar N increased significantly with each increase in N provided in the nutrient solution (P<0.01).

DOI:10.1093/ee/23.4.930

出版商:Oxford University Press    

年代:1994

数据来源: OUP