摘要:

Cucurbita pepoL. (zucchini) plants infected with zucchini yellow mosaic virus (ZYMV) for 4 wk were rejected as colonization hosts byAphis gossypiiClover (melon aphid) alatae in the field at a greater rate than un infected zucchini and plants infected for 2 wk. Using an electronic feeding monitor to examine the feeding behavior ofA. gossypiion plants treated similarly, the study found fewer probing events, more phloem contacts, and more nymphs produced on uninfected zucchini and plants infected for 2 wk, than on plants infected for 4 wk. When phloem contact was made on plants infected for 4 wk, alatae spent more time in salivary sheath formation and less time phloem feeding than alatae on uninfected plants, and plants infected for 2 wk. These colonization and feeding responses could enhance ZYMV acquisition from zucchini.

DOI:10.1093/ee/21.3.578

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Field experiments were conducted to examine interactions ofHeliothis virescens(F.), its natural enemies, and tobacco plants engineered to express low levels ofBacillus thuringiensisBerliner toxin. Survival ofH. virescenslarvae was measured in response to four treatments: (1) toxin-producing plants exposed to natural enemies, (2) toxin-producing plants caged to exclude enemies, (3) toxin-free plants exposed to enemies, and (4) toxin-free plants caged to exclude enemies.B. thuringiensistoxin mediated resistance caused a significant decrease in first-instar survival, and natural enemies caused a significant decrease in third-instar survival. Survival of uncaged first instars as a proportion of survival of caged first instars was significantly lower on toxic plants than control plants, indicating synergism of resistance and natural enemies. Among collections of artificially infested larvae, parasitism byCampoletis sonorensis(Cameron) was significantly higher on toxic plants than on control plants, another indication of synergism. Among collections of wild larvae and larvae censused in the field, parasitism usually did not differ between plant lines. Larval development ofH. virescenswas significantly slower on toxic plants than on control plants in two out of five trials. Prolonged vulnerability to natural enemies appeared to provide a mechanism for synergism. However, synergistic increases in mortality and parasitism were detected in two trials when development rates on toxic plants and control plants were equal, indicating existence of another mechanism.B. thuringiensistoxin-mediated partial resistance appeared compatible with natural enemies for control ofH. virescens. However, a simulation using a theoretical population genetic model suggested that synergism of the level measured in this study could accelerate pest adaptation to resistant plants.

DOI:10.1093/ee/21.3.586

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Larvae ofAnopheles albimanuswere collected on the Pacific coastal plain of Chiapas, Mexico, from 131 sampling sites representing different larval habitats. For each habitat the total percentage of emergent vegetation, floating vegetation, or both, percentage of cover of individual plant species, amount of phytoplankton, water conductivity, and the number of mosquito larvae collected in 30 dips were recorded. Individual habitats were classified into higher units, or habitat-types, by cluster analysis based on 37 environmental variables. Sixteen clusters, or habitat-types, were distinguished and defined by dominant plant species. Habitat-types were ranked by larval density and categorized as either low, medium, or high producers ofA. albimanus.

DOI:10.1093/ee/21.3.598

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Cage environments in the laboratory were used to study flea beetle,Phyllotreta cruciferae(Goeze), feeding, response, and longevity on oilseed rape (Brassica napusL.) and crambe (Crambe abyssinicaHochst.). Flea beetle feeding occurred almost exclusively in the light. Flea beetles fed significantly more on oilseed rape than on crambe in choice and no-choice tests. Residence time on oilseed rape also was longer. In choice tests, there was no difference in transition frequency between oilseed rape and crambe. In no-choice tests, Significantly higher transition frequency was observed on crambe. Mechanical wounding of the cotyledons of the two plant species did not influence flea beetle response or feeding. The effect of flea beetle density on the amount of feeding was described with a second-order polynomial regression, which suggests that the beetles need to aggregate in sufficient numbers to utilize a host optimally. In the long-term feeding studies, the amount of feeding per beetle differed significantly between oilseed rape and crambe during the initial 25 d, after which there were no significant differences. Flea beetles that fed on oilseed rape lived significantly longer than those that fed on crambe. There was no difference in longevity between males and females fed on the same plant materials. The results confirm that crambe is a less-suitable host for flea beetles than is oilseed rape.

DOI:10.1093/ee/21.3.604

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

It is assumed that many insects oviposit on food patches which present limited resources to developing offspring, and that this factor plays a role in determining the number of eggs a female lays per food patch. The role of such limited resources in the number of eggs laid by the bruchid beetleStator limbatus(Horn) on seeds ofCercidium floridum(Benth.) in the Sonoran Desert was assessed. Distributions of eggs per seed from field samples were examined first. These distributions were significantly different from Poisson distributions, suggesting nonrandom oviposition. On intact seeds with eggs, the most common number of eggs was 3 and 93% of the seeds had 1–10 eggs. The eggs on these seeds suffered various mortalities. The egg parasiteUscana semifumipennis(Trichogrammatidae) attacked eggs density-dependently (frequency of attack = 0.02 eggs per seed + 0.2). Density-independent mortality factors included embryonic deaths (0.20 ± 0.02 of all eggs laid), death of first instal's at the seed coat (0.31 ± 0.06 of larvae), and death of larvae inside the seed (0.12 ± 0.03 of larvae that entered the seed). Given these factors, the optimal number of eggs per seed that a female should lay to maximize the yield of offspring from a seed is 15, which is significantly greater than the number of eggs per seed commonly observed. At such high densities of eggs per seed, larval competition was not a mortality factor that could favor fewer eggs per seed. Very few larvae ever survived parasitism and embryonic development, and penetrated the seed coat. Hence, larval competition was minimal. Females laid few eggs per seed in the laboratory, as observed in nature, when seed availability was increased. It is suggested that oviposition byS. limbatusis determined by egg parasitism favoring few eggs per seed and seed availability. The implications of egg parasitism rather than larval competition in determining clutch size is also discussed.

DOI:10.1093/ee/21.3.610

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

The reproductive potential and longevity of adult females ofCatolaccus grandis(Burks) (an exotic parasitoid of the cotton boll weevil) were determined under laboratory conditions at four constant temperatures (25, 30, 35, and 40°C ± 1). The resulting data were used to calculate life tables and rates of increase at each temperature. The effect of food and water availability on longevity at 25, 30, and 35°C was evaluated on groups of 10 adult wasps. A female ofC. grandisoviposited means of 679.24,498.8,76.15, and 0.0 eggs at 25, 30, 35, and 40°C, respectively, and had a mean longevity of 63.55, 46.35, 20.8, and 9.0 d at the same four temperatures respectively. The net reproductive rate was 58.4, 28.35,4.3, and 0.0; the daily intrinsic rate of increase was 0.134, 0.159, 0.082, and 0.0; and the weekly rate of increase was 1.052, 1.327, 0.692, and 0.0 at 25, 30, 35, and 40°C, respectively. The food treatments that included honey significantly increased longevity with respect to those treatments that lacked it. Treatment including only water did not increase longevity significantly with respect to the control (no food or water).

DOI:10.1093/ee/21.3.620

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Malacosoma americanum(F.) andM. disstriaHübner were collected by black-light traps in eastern West Virginia in 1988–1990. Ten locations were sampled in 1988 and 1989 and 27 locations in 1990. Traps were operated at each location for 0.5-h intervals centered at 2100,2300,0100,0300, and 0500 hours. Factorial analyses of variance were performed on the quantity of each species collected in each time interval. Peak flight time forM. americanumoccurred at 2300 and 0100 hours whereas mostM. disstriaflew during 0300 and 0500 hours. Flight activity ofM. americanumwas unrelated to the presence ofM. disstria. However,M. disstriaflew significantly later at night, and was less abundant whenM. americanumwas present. Other research suggests that species withinMalacosomause similar sex pheromones. Separate flight activities of these species may help reduce interspecific pheromone attraction and aid the reproductive isolation of these species.

DOI:10.1093/ee/21.3.628

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Population parameters (mean generation time, intrinsic and finite rates of increase, and days for population to double) and the components of the intrinsic rate of increase (developmental and prereproductive times, total fecundity, percent immature mortality, and fecundity rate) were estimated forMonelliopsis pecanis,Monellia caryella,Melanocallis caryaefoliaein clip cages placed on pecan,Carya illioensis(Wang.) K. Koch, leaflets exposed to ambient environmental conditions in an orchard from mid-June to late October. Developmental and prereproductive times differed between species and decreased over time during the growing season. Females produced less progeny when their offspring remained in cluster in the cages for 4–6 d than when offspring were removed daily after counting. Mortality was not a factor in determining the rate of increase because of low mortality of nymphs during the reproductive periods.M. caryellahad the shortest developmental, prereproductive, and generation times and required less time for its population to double, yetM. caryellahad the highest mean total fecundity, fecundity rate, and intrinsic and finite rates of increase. Results are compared with studies from the literature done at constant temperatures.

DOI:10.1093/ee/21.3.632

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Larvae of the introduced blow flyChrysomya rufifacies(Macquart) were reared with larvae of the native blow flyCochliomyia macellaria(F.) on ground beef.C. rufifaciesreducedC. macellariasurvivorship at a variety of densities and proportions at both 22 and 29°C. No effect ofC. macellariaonC. rufifaciessurvivorship was observed. The addition ofC. macellariaincreased the time period from egg to adult inC. rufifacies. The reduction inC. macellariasurvivorship was so great as to outweigh any drop inC. rufifaciesfitness resulting from increased development time; the interaction appears to be a highly asymmetric case of competition. The interaction was not observed to influence the sex ratio of the resulting adults.

DOI:10.1093/ee/21.3.640

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

There are two methods of assaying for naturally occurring α-amylase inhibitors. In the first method, (E + I) + S, where E is the enzyme, I is the inhibitor, and S is the substrate, the enzyme and inhibitor are preincubated for a period of time and residual activity is measured by adding substrate (starch). In the second method, (I + S) + E, the inhibitor and substrate are combined and the reaction is started by addition of enzyme. Although the first method can be used to measure the concentration of +-amylase inhibitors in a given plant or plant structure, it may give a somewhat biased view of their in vivo activity. The second assay method may be a much more realistic way to assess the effectiveness of the inhibitors in a feeding insect, because at least in granivorous insects that feed on wheat endosperm, ingestion of starch and the proteinaceous inhibitors probably occurs simultaneously. Consequently, assays were conducted by the second assay procedure with amounts of +-amylase found in guts of the rice weevil,Sitophilus oryzae(L.), and with amounts of +-amylase inhibitors present in wheat endosperm. With these conditions, inhibition of enzyme activity was reduced significantly compared with the nearly complete inhibition possible with preincubation. These findings indicate that in vitro methodology should simulate in vivo conditions as closely as possible to allow a more precise evaluation of the potential of naturally occurring inhibitors as resistance factors against insects.

DOI:10.1093/ee/21.3.646

出版商:Oxford University Press    

年代:1992

数据来源: OUP