摘要:

The alfalfa weevil,Hypera postica(Gyllenhal), is the most important leafmass consumer of alfalfa,Medicago sativaL. However, little is known about how insect defoliation injury affects photosynthetic responses of alfalfa. Studies were conducted in 1990 and 1991 to characterize the gas exchange responses of alfalfa to simulated and actual alfalfa weevil larval injury. Gas exchange responses were observed for two levels of plant organization: (1) the remaining tissue of injured leaves and (2) the remaining leaves of defoliated plants. Transpiration and stomatal conductance rates for leaves with actual and simulated alfalfa weevil injury were greater than for leaves without defoliation injury. However, photosynthetic rates of leaves with simulated and actual alfalfa weevil injury were not significantly different from each other or from leaves without defoliation injury. Consequently, both simulated and actual alfalfa weevil injury did not seem to affect the photosynthetic apparatus of the remaining leaf tissue. Therefore, the principal effect of alfalfa weevil defoliation injury on photosynthetic responses of alfalfa was to reduce the amount of photosynthesizing leaf tissue, but not photosynthetic rates. Moreover, simulated alfalfa weevil injury techniques produced photosynthetic responses that were not significantly different from actual alfalfa weevil injury. Defoliated plants responded to simulated alfalfa weevil injury by altering the normal senescence pattern of the remaining leaves. In particular, leaves of defoliated plants maintained higher photosynthetic rates than corresponding leaves of control plants, which showed normal senescence patterns of decreasing photosynthetic rates. As defoliation injury increased in magnitude, leaf senescence of the remaining leaves proceeded at a progressively slower rate. Delayed leaf senescence seems to be a plant compensatory response to alfalfa weevil defoliation injury.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.501

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Feeding and oviposition preferences of adult cottonwood leaf beetles,Chrysomela scriptaF., were evaluated among leaf age classes by leaf plastochron index (LPI) for sixPopulusclones (IS-31, NC-5260, NC-5263, NC-5264, NC-5322, NC-5334) under controlled greenhouse conditions. Significant differences among clones and leaf age classes in feeding and oviposition in both multiple-choice and no-choice tests were found. Clones NC-5264 and NC-5334 were the most preferred for both behaviors in the multiple-choice tests. The most-preferred leaf age class for feeding was LPI 3 for both the multiple-choice and no-choice trials. In the multiple-choice oviposition tests, LPIs 3 and 4 were preferred and LPI 3 was most highly preferred in the no-choice tests. Quadratic relationships between leaf consumption and percentage of leaf consumed and leaf age class are suggested by the data from both types of tests. Direct correlations were found between leaf consumption and percentage of leaf consumed and the distribution of egg masses among the leaf age classes.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.508

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Studies of the metabolic fate of14C-labeled gossypol inHeliothis virescens(F.) found radioactivity mainly in the fat body of fifth-stadium larvae, the dissolved tissues of 4-day-old pupae, the abdomen of newly emerged moths, and the larval frass.14C-labeled gossypol was eliminated as a respiration product from third to fifth instars, and from prepupa to adult. Gossypol was excreted in the larval frass as a free compound and as a conjugate. Analysis of labeled frass extracts by high-performance liquid chromatography indicated that the ethyl acetate and methyl alcohol extracts contained the highest concentrations of free and conjugated gossypol, respectively, Two metabolites from frass ofH. virescenslarvae were isolated and identified as derivatives of gossypol containing six glucose moieties attached to the gossypol nucleus.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.518

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Cabbage webworm,Hellula rogatalis(Hulst), development on broccoli was determined at five constant temperatures ranging from 15 to 35°e. At 15°e, egg to mature larva was 119.4 d, but larvae failed to pupate. Development from egg to death of the adults was 89.9, 42.8, 34.0, and 22.8 d at 20, 26, 30, and 35°e, respectively. Fecundity increased with temperature between 20 and 30°e, with a maximum of 161.5 eggs per female at 30°e, but decreased to 8.2 at 35°C. Most eggs were laid on the upper surface of the broccoli leaf. No eggs hatched at 10°C, but at 15°C, egg hatch was 19.1%, and increased to 89.3% at 26°C. There were five instars; head-capsule width for the first through fifth instars was 0.19, 0.29, 0.49,0.78, and 1.20 mm, respectively. The first two instars mined the leaf; later instars fed on the under surface of rolled leaves, within spun webs, and the last two instars fed on the leaf as well as the midrib, breaking it in two. The constant temperature data obtained were used to construct developmental time function curves using the population model design system software program.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.527

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Three young loblolly pine plantations grown on contrasting soil types produced quantitatively and qualitatively different host material for pine tip moths during 1985 and 1986. Amounts, periodicity, and availability of soil moisture regulated internal moisture conditions within host trees. Host xylem moisture potential in conjunction with soil nutrient status governed tree growth and influenced pine tip moth infestation rates. Pines on a sandy site exhibited the poorest growth with lowest infestation rates, indicative of low-quality hosts with little if any tolerance to damage. A clayey site produced vigorous plant growth with moderate infestation rates. The less apparent hosts appeared capable of withstanding pine tip moth attack and overcoming damage. Pines on a loamy site grew at moderate rates and received the highest infestation rates. This moderate growth indicated susceptible stand conditions.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.534

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Aphid landing rates were monitored with horizontal mosaic green pan traps in monocultures of soybean,Glycine max(L.) Merrill, and in additive mixtures of soybean with dwarf or tall isolines of sorghum,Sorghum bicolor(L.) Moench.Rhopalosiphum maidis(Fitch) colonized sorghum whorls and was the major species caught in pan traps. Weekly aphicide spot applications to sorghum whorls, starting at 36 d after planting, did not suppressR. maidiscolonies significantly until after the third application. Landing rates ofR. maidisalatae were similar in treated and untreated crop mixtures. The lack of a significant difference may have resulted from immigration ofR. maidisalatae from outside the experimental field but inefficient colony suppression may have produced similar results. Mixed cropping reduced landing rates ofAphis gossypiiGlover,Aphis helianthicomplex, andLipaphis erysimi(Kaltenbach) on sorghum plants, andR. maidison soybean plants. Generally, landing rates were equally reduced in the mixtures with tall or dwarf sorghum. The percentage of ground covered by vegetation, which was less in monocultures than in mixtures, proved to be more important than crop height in reducing aphid landing rates. All aphid species landed randomly on soybean and sorghum plants within dwarf sorghum mixtures. However, in tall sorghum mixturesAphis neriiBoyer de Fonscolombe andA. gossypiipreferred to land on soybean whereasAphis spiraecolaPatch landed more often on sorghum. LandingR. maidisalatae did not show a preference for sorghum or soybean in the crop mixtures. Different sensitivities to microclimatic conditions may explain these behavioral patterns.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.542

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

In four mixed media composed of (1) brown and polished rice,Oryza sativaL., (2) brown and rough rice, (3) polished and rough rice, and (4) brown, polished, and rough rice, feeding and oviposition of the rice weevil,Sitophilus oryzae(L.), were observed. In all media, the weevil rarely exploited rough rice. The rice weevil fed on brown rice more frequently than on polished rice, but did not concentrate on brown rice in the media containing both brown and polished rice. The feeding preference index for brown rice over polished rice was ≍1.9. Females laid more eggs on brown rice than on polished rice. In the media containing both brown and polished rice, females laid eggs exclusively on brown rice; the preference index for brown rice over polished rice was ≍19.3. Mortality of the weevil during development in the medium without brown rice was significantly higher than in the media with brown rice. Life table statistics for the weevil in the four media showed that brown rice was the critical factor determining population development. Thus, the weevil's strong oviposition preference for brown rice allows it to maximize its fitness when feed with a variety of resources of different qualities. The relative impact of oviposition versus feeding preferences of the weevil on its reproductive success is discussed.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.549

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

The sex ratio ofBemisia tabaciwas examined in the field, and ranged from a female-biased condition early in the season to male biased at summer's end. Laboratory studies showed that young females laid proportionately more female-producing eggs than older females, and that females with access to males throughout their life laid a higher proportion of females than those that mated only once shortly after emergence. These laboratory results provide at least partial explanations for the sex ratios observed in the field.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.556

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Lifetime oviposition was measured for femaleDelia antiqua(Meigen) caged individually with cups of moist sand or surrogate onions possessing combinations of host-plant color and chemical stimuli. Females laid more eggs on surrogates than on sand and laid more eggs on surrogates coated with synthetic onion volatiles (n-dipropyl disulfide, Pr2S2)than on untreated surrogates. Surrogate color had no effect on fecundity. Flies deprived of exposure to Pr2S2took longer to initiate oviposition and took longer to complete ovipositional cycles. The presence of untreated surrogates increased the percentage of eggs laid in ovipositional cups from 14 to 74%, whereas the presence of Pr2S2or host-plant color resulted in nearly all eggs being laid in cups. The number of eggs retained at death did not differ among treatments. The results suggest that differential oviposition may have resulted from reduced rates of egg maturation as a consequence of accumulation of unlaid eggs. Host specialization by the onion fly is probably due to ecological factors as well as an ovipositional preference for onion.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.560

出版商:Oxford University Press    

年代:1992

数据来源: OUP

摘要:

Despite the economic importance of the corn leafhopper,Dalbulus maidis(DeLong&Wolcott), little is known about how this maize pest and its congeners survive the dry winter in Mexico. In the field,Dalbuluspopulations were monitored weekly with yellow sticky card traps for 18 mo at three sites in Jalisco, Mexico. The sites included a maize field,Zea maysL.; a natural stand of a perennial teosinte,Zea diploperennisIltis, Doebley&Guzman; and a natural population of gamagrasses,Tripsacumspp., which are maize relatives. At all sites, highest catches ofDalbulusadults occurred during the dry season between October and March. In a laboratory study to test the survival of adultDalbulusleafhoppers without their host plants, significant differences were detected among leafhopper species. When denied all food and water (absolute drought),Dalbulusspecies that specialize on maize were more tolerant than those that specialize on gamagrass. Adults reared under environmental conditions that simulate the beginning of the wet season (June-reared) were less tolerant of absolute drought than adults reared under early dry-season conditions (October-reared). When provided water but no food, October-rearedD. maidislived significantly longer than June-rearedD. maidis. Survival of females under water-only conditions was significantly longer than that of males. Field observations revealed that gamagrass-specializingD. gelbusDeLong andD. quinquenotatusDeLong&Nault overwinter as continuously developing populations on their hosts. In contrast, our data indicate thatD. maidisoverwinter as active adults that can subsist, at least in part, on free water in the absence of host plants until the summer rainy season begins. Surviving adults then migrate locally to newly planted maize fields.

ISSN:0046-225X    

DOI:10.1093/ee/21.3.566

出版商:Oxford University Press    

年代:1992

数据来源: OUP