摘要:

INSECTS INTRODUCED to new environments without their natural enemies frequently attain high population densities. Outbreaks of insects that are free of natural enemies and their suppression by introduced biological control agents are evidence that predators and parasitoids can limit or regulate host density (Huffaker 1970). However, most biological control projects are not successful. The introduction of predators and parasitoids has only reduced host densities sufficiently to replace chemical control in approximately 16% of more than 600 projects (Hall et al. 1980, Ehler&Andres 1983). This low success rate includes failures of the predators and parasitoids to become established and failures of established agents to reduce host density. These failures occur for several reasons but, it is possible that only a few species of predators and parasitoids have the potential to suppress host population density to any great extent. An alternative interpretation is that a complex of natural enemies is necessary to suppress host population densities and until this total complex is reestablished, successful biological control will not be achieved.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.541

出版商:Oxford University Press    

年代:1989

数据来源: OUP

摘要:

Developmental thresholds and thermal requirements for different stages ofSpodoptera litura(F.) fed on groundnut leaves were determined under constant laboratory conditions and in the field. An average of 64 degree-days (DD) above a threshold of 8°C was required from oviposition to egg hatch; the larval period required 303 DD and pupal stage 155 DD above a 10°C threshold; females needed 29 DD above a 10.8°C threshold from emergence to oviposition. Fifth and sixth instars accounted for about 50%of the total larval requirement under laboratory and field conditions. The response of various stages ofS. liturato temperatures under constant laboratory conditions was similar to that under field conditions. The upper developmental threshold temperature of all stages was 37°C; 40°C was lethal.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.548

出版商:Oxford University Press    

年代:1989

数据来源: OUP

摘要:

Before cold acclimation, diapausing mature larvae ofHomoeosoma electellum(Hulst) have glycogen levels two times greater than nondiapausing mature larvae, trehalose levels are 30 times greater, and larvae have a lower supercooling point by approximately 8°C. Significant increases in trehalose occurred in diapausing larvae kept at 5°C for 7 and 18 d and at 0°C after 10 d. In most cases, there was a sufficient concomitant reduction in glycogen to account for the trehalose increases. Nondiapausing larvae in the temperature treatment groups of 10, 5, and 0°Cshowed significantly greater trehalose levels over initial values; yet these levels are almost two times lower than initial levels in diapausing larvae and three times lower than the greatest levels achieved in this study by diapausing larvae cold-acclimated to 0°C. No specific relationship was found between temperature acclimation and supercooling capacity in diapausing or nondiapausing larvae. Nondiapausing larvae died after being held at −10°C for 1 d, whereas 44% of the diapausing larvae survived to pupation after 3 d of exposure.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.552

出版商:Oxford University Press    

年代:1989

数据来源: OUP

摘要:

The photoperiodic responses of two clones of pea aphid,Acyrthosiphon pisum(Harris), collected on the same day in the same field are compared. The clones differ not only in the photoperiods at which sexuals first appear, but also in the rate of transition from production of one morph to another. When these clones are compared with other pea aphid clones for which data on production of sexuals are available in the literature, further differences in pattern of production of sexuals become apparent. These comparisons further emphasize the need to observe a sample of clones when attempting to describe any aspect of the species characteristics of aphids.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.558

出版商:Oxford University Press    

年代:1989

数据来源: OUP

摘要:

The annual diapause phenology, larval development, and adult emergence of tobacco budworm,Heliothis virescens(F.), was studied under insectary conditions at Phoenix, Ariz., from August 1986 to September 1987. The percentage of pupae entering fall diapause peaked at approximately 97% on 16 November 1986 and remained high (near 80%) through February 1987. The percentage of pupae entering summer diapause reached a maximum of 51.7% on 19 July as mean daily temperatures increased to 30°C. Moths emerging from nondiapausing and diapausing pupae contributed to major moth peaks in the fall (23 August to 1 December) and spring (1 April to 15 May) months. Very little moth emergence was observed from 15 December to 1 April. Larvae required an average of 10–88 d to complete development, depending on annual temperature and photophase fluctuations. Larval mortality (range, 1–93%) also was highly correlated with larval developmental time. Pupal developmental time varied greatly among cohorts: nondiapause, 10–45 d; fall diapause, 40–190 d; and summer diapause, 28–105 d. Pupal mortality for fall diapause (43.5%) also was significantly higher than that of other pupae. Lower and upper temperature thresholds for larval and pupal development, taken from the literature, were modified using coefficient of variation analyses of degree-day accumulations. Based on the coefficient of variation method, lower and upper thresholds for larvae, nondiapausing, fall-diapausing, and summer-diapausing pupae were 11.25–32.0, 12.8–34.0, 12.8–32.0, and 12.8–30.0°C, respectively. Use of this information to develop a season-long model ofH. virescensphenology is discussed.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.563

出版商:Oxford University Press    

年代:1989

数据来源: OUP

摘要:

Larval and pupal parasites were collected before and after a mating disruption test ofRhyacionia zozana(Kearfott) to determine if the pheromone treatment affected either the species distribution or abundance of the parasite complex. Total percentage of parasitism was not changed because of the disruption treatment. In treated areas, however, abundance of the most numerous moth parasite,Glypta zozanaeWalley and Barron, was reduced significantly below check plantation levels. In contrast, abundance of the pupal parasiteMastrus aciculatus(Provancher) was higher in pheromone-disrupted areas. No changes in the sex ratios of these species were attributable to the pheromone treatment. Parasite community structures were compared using a similarity index. The degree of likeness between treated and check plantations decreased after disruption, probably because of the changes in the incidence of parasitism byG. zozanaeandM. aciculatus. Accounting for parasitism and reduced mating, surviving host populations in check plantations were over four times greater than in pheromone-disrupted areas. The importance of the host's sex pheromone as a potential kairomone and effects of changes in the host density caused by the mating disruption treatment on the associated parasite complex are discussed.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.570

出版商:Oxford University Press    

年代:1989

数据来源: OUP

摘要:

In the Mississippi Delta, roadside vegetation serves as spring habitat for the bollworm,Heliothis zea(Boddie), and tobacco budworm,H. virescens(F.). Predators ofHeliothisalso are found in this habitat; they include species of spiders and ground beetles. Test plots of two species of grasses, planted with and without ammonia nitrate applications at planting, and both planted in combination with six species of legumes (total of 16 treatments), were established along U. S. Highway 61 in Washington County, Mississippi in the fall of 1984. The effect of the treatments on spiders and ground beetles during March, April, and May 1985 was determined by sampling populations of these predators with pitfall traps. Treatments differed little in species diversity or in species dominance for these two groups of predators. None of the treatments had a significant effect on the numbers of ground beetles, lycosid spiders, or total numbers of spiders captured. Consequently, based on their effect on these important groups of beneficial arthropods, none of the treatments was eliminated for possible use as roadside vegetation in the Mississippi Delta to aid in the control of the F1generation ofHeliothis.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.575

出版商:Oxford University Press    

年代:1989

数据来源: OUP

摘要:

Thirteen species ofOsmiabees were studied for 2 yr to determine their pollen foraging behavior in terms of individual and population constancy. Two species,Osmia californicaCresson andO. montanaCresson, were family-level oligoleges on Asteraceae. Two of the eleven polyleges were generalist pollen foragers:O. densaCresson showed no statistical preference andO. albolateralisCockerell showed a significant preference, but for two different pollens. NineOsmiapolyleges showed a local specialization for either a genus or family of flowering plants that was shown to be statistically significant:O. raritatusMichener andO. sladeniSandhouse forTrifolium(Fabaceae);O. brevisCresson forPenstemon(Scrophulariaceae); andO. bruneriCockerell,O. callaCockerell,O. indeprensaSandhouse,O. kincaidiiCockerell,O. lignariaSay, andO. nanulaCockerell forPhacelia(Hydrophyllaceae). Individual constancy measures were statistically higher for the oligoleges. Niche breadths and the number of flower species visited were not statistically different among the foraging groups. When tested against the expected oligolege and polylege niche breadths, observed oligolege niche breadths were not statistically different; however, polylege niche breadths were statistically lower than expected. TheOsmiaspecies showed flower partitioning and overlap; the overlap occurred on the most abundant flowering species in the study area. We have no indication or evidence of competition for pollen resources among the 13 species studied.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.582

出版商:Oxford University Press    

年代:1989

数据来源: OUP

摘要:

The enemies hypothesis holds that predatory insects and parasitoids are more effective at controlling populations of herbivores in diverse systems of vegetation than in simple ones. Eighteen studies that tested the enemies hypothesis are reviewed. Of those studies reporting mortality from predation or parasitism, nine found higher mortality rates in diverse systems; two found a lower mortality rate; and two found no difference. The mechanisms that are thought to underlie the enemies hypothesis and directions for future research are discussed. Evidence suggests that the enemies hypothesis and the resource concentration hypothesis (which predicts that herbivores more easily find, stay in, and reproduce in monocultures of host plants than in polycultures) are complementary mechanisms in reducing numbers of herbivores in diverse agricultural systems.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.590

出版商:Oxford University Press    

年代:1989

数据来源: OUP

摘要:

The phytophagous arthropod community on apple was studied in Virginia, West Virginia, Pennsylvania, and New York in 1983 and 1984. Managed, “organic” (reduced management), and abandoned orchards were sampled and the arthropod communities therein were compared to examine the effects of orchard management on the community. Williams's index, species richness, and evenness all showed significantly greatest diversity in abandoned orchards, intermediate diversity in “organic” orchards, and least diversity in managed orchards. Diversity in the “organic” orchard decreased during the 2 yr of study, showing the cumulative effect of orchard management on the system. Similarity among orchards, within management class, ranged from 28 to 60%. Percentage of similarity and diversity indices indicated that cultivar and orchard age differences were not significant factors in comparisons among orchards. Communities were dominated by r-selected species in managed orchards and K-selected species in abandoned orchards. Community structure is hypothesized to be regulated by human-induced, environmental factors in managed orchards and by natural enemies in abandoned orchards.

ISSN:1754-5692    

DOI:10.1093/ee/18.4.600

出版商:Oxford University Press    

年代:1989

数据来源: OUP