摘要:

The duration of feeding and relative amounts consumed by Hessian fly,Mayetiola destructor(Say), larvae on resistant and susceptible seedling wheat plants labeled with [35S]L-methionine was investigated. Plants were labeled over 48-h periods from initial infestation to 8 d after infestation, and the uptake of35S by larvae determined. With the H3and H5genes for resistance, the uptake of35S by larvae was significantly less than on susceptible controls, and suggested that the larvae were unable to initiate or maintain sustained feeding on the resistant plants. With the H6gene for resistance, uptake of35S by larvae during the first 48 h was not significantly different from that on susceptible controls, but then declined between 48 and 96 h. These data indicate that with the H6gene, larvae fed actively for the first 48 h after infesting the plants, then ceased their feeding between 48 and 96 h. All larvae on resistant plants were alive 48 h after infesting plants and approximately 60% were alive 96 h after infesting resistant plants. All larvae on resistant plants were dead by 144 h after infestation. Results are discussed in the context of possible mechanisms of action for the resistance genes investigated.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.494

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Black locust trees (Robinia pseudoacaciaL.) of variable age and height were studied in relation to vertical distribution of larval tunnels made by the locust borer,Megacyllene robiniae(Forster), in Maryland. Tunnel concentrations were negatively correlated with height above ground level and with bolt diameter. With greater tree size, attacks were concentrated higher on the main trunks. However, upper extremities of trees of all sizes and ages were lightly attacked.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.501

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Population densities ofEmpoascaleafhoppers and their major natural enemies (Anagrus parasitoidsandErigone spiders) were compared on squash in pure and mixed stands. Adult leafhoppers were more abundant in monoculture than on squash in polyculture, but squash in polyculture harbored more nymphs than did plants in monoculture. Therefore total leafhopper densities as prey were similar on squash in monoculture and on squash intercropped with cowpea and corn. These results are consistent with general theory on the response of polyphagous herbivores to vegetational diversity. The specialist parasitoid was not enhanced in mixed stands, but the generalist predator exhibited greater densities on intercropped squash. Thus, host range or range of prey might be important for predicting enemy response to vegetational diversity, as is host plant range for predicting the effects of plant diversity on herbivore densities.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.505

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The effects of cover crops and crop residues on seedcom maggot,Delia platura(Meigen), population dynamics in soybeans (Glycine maxMerrill) were studied when incorporated into the soil before crop planting and when left on the soil surface where soybeans are planted, using no-tillage practices. Crop covers and residues had a dramatic effect on seedcorn maggot populations; highest numbers were obtained when cover crops were incorporated. When no-tillage planting methods were used, no enhancement of populations was obtained. Significantly greater numbers ofD. platuraadults were obtained from plots where alfalfa (Medicago sativaL.) was incorporated into the soil, followed by rye (Secale cereale(L.)), soybean residue, and least with corn (Zea maysL.) residue. Orthogonal comparisons indicated that more seedcom maggots were obtained when a live, green cover was incorporated into the soil than with dead crop residue. Orthogonal comparisons also showed that more adults were collected when a legume was incorporated compared with a grass.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.510

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Phytophagous insects representing 106 species, 36 families and seven orders, and one eriophyid mite, fed on seepwillow,Baccharis salicifolia(Ruiz Lopez and Pavon) Persoon (=glutinosaPersoon) (Asteraceae: Astereae) in the study area. Sixteen (18%) of these were economically important. About 50% of the species were polyphagous, 10% apparently feed only on plants in Asteraceae, and 6% were apparently restricted to feeding in the genusBaccharis. Seepwillow was a host for about 82 species of foliage- and sap-feeding insects. Flower-visiting insects, representing 37 species, 15 families and three orders, were collected from flowers of seepwillow between July and December.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.515

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

The influence of minor and nonhost vegetation on bean,Phaseolus vulgartsL., host plant acceptance by the potato leafhopper,Empoasca fabae(Harris), was studied, with emphasis on the influence of tomato,Lycopersicon esculentumMill. Cage environments in the laboratory and greenhouse were used to observe leafhopper movement and arrestment and to evaluate performance criteria, including feeding and oviposition. The presence of tomato vegetation suppressed total excreta production (an index of feeding) by 43%. Reduced excreta production was a result of considerable residence time on tomato. In oviposition choice tests, only 28% of the eggs were laid on bean in proximity to tomato. No-choice tests gave similarly significant results. Cabbage also reduced oviposition when in proximity to bean. In choice tests, only 32% of the eggs were laid on bean in proximity to cabbage. There were no differences in the average length of time on bean during each arrestment bout in treatment cages containing a combination of bean and companion plant leaves versus the control containing only bean leaves. When evaluating leafhopper movement frequency from surface to surface (i.e., the two leaves and cage surfaces), no significant difference was found when comparing the bean control with the bean and tomato treatment. It is suggested that tomato plants can directly reduce the interaction between bean plants and leafhopper through an extensive “nonproductive” residency time on tomato plants. The importance of evaluating insect and plant interactions based on multiple criteria is discussed.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.524

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

This study describes the influence of tomato,Lycopersicon esculentumMill, and bean plant,Phaseolus vulgarisL., intercropping on the potato leafhopper,Empoasca fabae(Harris). The field design consisted of a single density of snap bean plants intercropped with a gradient of tomato plant densities. Leafhopper oviposition, nymph and natural enemy populations, and plant growth were monitored throughout two seasons. A complementary laboratory study analyzed the potential influence of host plant quality upon its acceptability for oviposition by potato leafhopper. Leafhopper densities in medium to high density intercrop subplots were>25% of those populations on bean planted alone, during periods of high leafhopper population densities. Differences in nymphal counts between treatments were a function of oviposition, not differential nymphal mortality from natural enemies or host plant resistance. Differences in tomato plant density across treatments did not fully account for differences in leafhopper densities. Reduced bean host plant acceptability was observed when choice tests were conducted using beans grown under different fertilizer levels. Up to 76% of the eggs were laid in plants containing the greatest amount of total nitrogen. Although tomato is believed to have directly reduced leafhopper densities in the intercrop treatments, the additional effect of host plant quality was also shown to be a potentially important factor.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.534

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Pear psylla,Cacopsylla pyricola(Foerster), overwinters as an adult in reproductive diapause that is initiated and maintained by short photoperiod. In autumn, females have immature ovaries and few are mated. Coincident with warm field temperatures in late winter, their ovaries mature and most of them become mated. The mean number of spermatophores per female varied from 5.3 to 16.5 (range, 0–63) among populations from three orchards sampled in the spring. Newly emerged laboratory-reared winterform (diapause) males have active sperm in the testes and seminal vesicles. In autumn, field-collected winterform males have sperm in the seminal vesicles, but the rate of insemination of females is very low if males are held in the laboratory under a short photoperiod of 10:14 (L:D). The rate of insemination increases greatly after such males are conditioned at a long photoperiod of 16:8 (L:D) for about 10 d. As winter progresses, there is a decrease in the duration of the conditioning required to permit mating. The ability of males to mate with females appears to be under control of the diapause syndrome.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.544

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Mating activity of pear psylla,Cacopsylla pyricola(Foerster), with emphasis on the morphologically distinctive overwintering winterform generation, was characterized in the laboratory. Generally, one spermatophore was passed per copulation. Presence of light, size of the mating arena, and the number of leaves in the arena affected mating frequency; the highest mean frequency observed was 9.18 matings per 24 h. Diapausing psylla males, after being conditioned under long photoperiod (16:8 [L:D]), mated significantly more often than those conditioned under a photoperiod of 12:12 or 10:14 (L:D). The photoperiodic experience of the female did not affect mating frequency. Visual observation of behavior revealed that the winterform males conditioned under short days made as many sexual advances as winterform males conditioned under long days, but diapause males were rejected by the females. Pairings of winterform females with summerform males had significantly fewer inseminations compared with pairings involving the same seasonal forms; there is a behavioral barrier to mating between the generations.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.551

出版商:Oxford University Press    

年代:1990

数据来源: OUP

摘要:

Ecology ofAcigona ignefusalisHampson, which is an important insect pest of pearl millet in the Sudano-Sahelian zone of West Africa, was studied in Senegal. The pest had two or three generations in a crop season with maximum activity in August–October. Pearl millet and a grass,Pennisetum purpureum Schum., supported a higher population of borers than sorghums. Vertical distribution of borers in the millet plant was influenced by insect feeding site, plant height, stalk thickness, internodes, and stalk condition. Millet stalks and stubble left in the field after harvest and stalks used for housing harbored the diapaused borers during off-seasons. Partial burning of infested green stalks proved to be effective and practical in checking carry-over of the pest.

ISSN:1754-5692    

DOI:10.1093/ee/19.3.558

出版商:Oxford University Press    

年代:1990

数据来源: OUP