摘要:

In some cases, infection by plant viruses can alter host plant quality for homopterous insects. In these experiments, adult whiteflies from a population ofBemisia tabaci(Gennadius) that had been reared continuously on pumpkin plants for more than five years, were exposed to six plant species infected with one of four whitefly-transmitted plant viruses. The life history traits of whiteflies on virus-infected hosts were compared to those of whiteflies exposed to corresponding healthy hosts. Significant differences were found in progeny survival and oviposition rate among the six healthy hosts. Survival on healthy hosts ranked as follows: zucchini>cantaloupe = cotton = pumpkin>lettuce = tomato. Oviposition and immature survival rates varied between healthy and virus-infected host plants. The mean proportion of eggs surviving to adulthood was higher on pumpkin plants infected with watermelon curly mottle strain of squash leaf curl virus (WCMoV/SLCV) than on healthy pumpkin. Significantly lower mean proportion of offspring survived to adulthood on WCMoV/SLCV-infected zucchini, chino del tomate virus-infected tomato, and cotton leaf crumple virus-infected cotton compared to whiteflies on healthy control plants. For other virus-infected–healthy combinations, there were no significant differences in survival rates. No correlation was observed between levels of total free amino acids in healthy and infected plants and rates of oviposition or survival. The lack of correlation between oviposition and survival rates on healthy and infected plants, suggests thatB. tabacidoes not assess host suitability to regulate oviposition with respect to the projected host suitability for offspring survival.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1102

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Eleven peach cultivars were evaluated at Thorsby, Ala., and Byron, Ga., for bark prunasin content, bark thickness, peachtree borer larvae entrance sites, and peachtree borer adult emergence. Significant differences in larval weight occurred after 21 d of feeding on four different peach cultivars but were not evident after 42, 64, or 88 d. Prunasin content and bark thickness exhibited considerable variation with time, location, and cultivar. A significant positive correlation was found between prunasin content and emergence in 1 of 3 yr. In that year, larval entrance sites were positively correlated with emergence. This phenomenon was attributed to the presence of an ovipositional stimulant on trees that had previously supported the successful development of peachtree borers rather than an oviposition preference for trees with high prunasin content. A statistical correlation between peachtree borer emergence and bark thickness was not shown. However, the cultivar from which the greatest emergence occurred also had the greatest bark thickness. Results indicated that differences in host suitability exist among cultivars, but that host suitability may vary with environmental conditions.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1108

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Two studies were conducted to provide information on the development of potato leafhopper,Empoasca fabae(Harris), eggs, male nymphs, and female nymphs under fluctuating temperatures, and on the ovipositional threshold of adult gravid females. Mean developmental times were measured forE. fabaeeggs, male nymphs, and female nymphs under three fluctuating temperature regimes of 8–19, 10–21, and 13–24°C. These regimes were representative of January, February, and March daily temperatures in southern Louisiana, an overwintering site forE. fabae. Eggs developed in 34.9 ± 5.77 d, 28.8 ± 4.87 d, and 15.9 ± 2.09 d for the three regimes, respectively. Male nymphs developed in 47.8 ± 9.7 d, 39.1 ± 7.96 d, and 22.7 ± 3.3 d for the three regimes. Female nymphs developed in 47.0 ± 9.9 d, 39.4 ± 4.89 d, and 24.9 ± 3.11 d for the three regimes. A five temperature regimes database was created by combining these developmental times with developmental times reported by Hogg (1985) for similar but warmer fluctuating regimes. Logarithmic developmental rate equations, based on hourly temperature data, were developed from these data. The accuracy of these developmental equations was verified with independent data reported in the literature. Only females reared from eggs in the 13–24°C regime oviposited as adults. The constant temperature oviposition threshold forE. fabaewas determined. Adult gravid females oviposited at 10°C, but not at 9°C. The estimated oviposition threshold was 9.5°C. Gravid females placed in the fluctuating regimes of 8–19°C and 10–21°C continued to oviposit. A factor inhibiting ovarian development in females reared from eggs under these two regimes was hypothesized.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1113

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Field censuses were combined with laboratory rearing and dissection to investigate the frequency of density-dependent predation and parasitism of 13 phytophagous insect species associated with the goldenrod,Solidago altissima. Only 11% of the correlations between mortality and density were statistically significant. However, of those relationships that were significant, all were positive in sign, indicating a trend toward direct density dependence. Mortality of nonoutbreak species, with their potentially more stable dynamics, was not more likely to be density dependent than was that of outbreak species. Predation and parasitism showed no difference in the frequency of positive relationships, nor were suites of parasitoids more likely to exhibit direct density dependence than individual parasitoid species.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1121

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

We compared the within-clone distribution and survival patterns of a tenthredinid sawfly,Euura exiguaeSmith, with those of a chrysomelid leaf beetle,Disonycha pluriligata(Leconte). Both of these insects are closely associated with the same host species, coyote willow (Salix exiguaNuttall), but the first is noneruptive and the second is eruptive in nature, and we have not discovered coexisting populations. Sawfly galls were significantly more abundant and larvae survived significantly better on young willow ramets than on older ones. However,Disonychaadults were more evenly distributed throughout willow clones and larvae survived relatively well on all ramet age classes tested. We describe essential differences between eruptive and noneruptive insect species based on preference and performance characteristics, and basic differences in life history. The key features in the noneruptive species probably are a tight relationship between oviposition preference for long shoots on younger plants, coupled with high larval performance on such shoots. Vigorous shoots provided a limited resource, constrainingEuurato show latent population dynamics. For the eruptive species, oviposition preference and larval performance were dissociated because females laid eggs in the ground, and could not evaluate plant quality relevant to larval feeding. Larvae then fed generally on almost any plant they climbed, and they defoliated many plants. With the high carrying capacity provided to larvae by all foliage in a willow stand, populations were not constrained by plant resources to remain at low densities, and they erupted.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1129

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The lack of data on temperature-dependent development of instars ofLiriomyza sativaeBlanchard is an impediment to research on biological control of this pest because parasitoids will likely interact differently with each instar. In this study, development times of eggs and instars ofL. sativaewere determined at constant temperatures of 20, 25, 30, and 35 ± 1°C onPhaseolus lunatusL. ‘Henderson’. Development rates of eggs and larvae increased linearly with temperature up to 35°C (r2≥ 0.95). More than 91% of the variation in development rate of first and second instars was explained by temperature, whereas temperature explained only 42% of the variation in third-instar development rate. A part of the variation in development rate of third instars may be explained by the fact that the designated end point of this stadium (emergence of third instars from leaves) occurred only during the photophase. Overall, 99.9% of larvae emerged from leaves after 95 degree-days (DD) (threshold temperature, 10°C). When the constant temperature data were used to parameterize a stochastic phenology model forL. sativae, the model predicted that 50% of the population would advance beyond the egg and first-, second-, and third-instar stages by 39.2, 67.0, 85.5, and 101.2 DD, respectively. The model predicted peak proportions of the population to be in first, second, and third stadia at 52.7, 76.1, and 93.2 DD. Pooled data from two fluctuating temperature experiments resulted in very similar estimates of timing of peak stage proportions (51.3, 74.4, and 94.1 DD, respectively). Degree-day values at peak stage proportions were used successfully to determine the temperatures required to advance members of a cohort to a particular stadium at a given time, thereby facilitating experiments examining interactions of parasitoids with each larval instar.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1134

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Development time, head capsule diameter, pupal weight, and mortality were measured for the mimosa webworm,Homadaula anisocentraMeyrick, under five constant-temperature regimes. The data were subjected to traditional linear regression techniques as well as to computer-assisted modeling procedures. Minimum development thresholds for the immature life stages fell within a range of 8.5–13.0°C. Approximately 70, 280, and 135 degree-days above a 12.3°C threshold were required to complete egg, larval, and pupal development, respectively.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1141

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Regardless of the photoperiodic condition experienced by nymphs ofGerris lacustris latiabdominisMiyamoto, a long-day photoperiod of 14:10 (L:D) after the last ecdysis induces stronger positive phototaxis from day 10 or day 17 in females, and from day 26 or day 29 in males than does a short-day photoperiod (10:14 [L:D]). The abrupt reduction in the photophase from 15.5–15.25 h (including twilights) in the field to 14, 12, or 10 h, weakens the strong positive phototaxis of adult specimens in the summer. However, an abrupt change from ≍15.5 h (including twilights) in the field to 18 or 6 h has no effect on positive phototaxis. In the field, weakening of positive phototaxis in July and August is induced by the decrease in daylength after the summer solstice. This weakening appears to be an adaptation to rice paddy habitats in which water surfaces rapidly disappear during August and early September in Kochi. It is associated with early migration to diapause sites, which reduces habitat overlap and the possibility of competition with the larger species,Gerris paludum insularisMotschulsky.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1149

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

The pteromalid waspMuscidifurax zaraptorKogan&Legner, a solitary pupal parasite of house flies and stable flies, was released in May adjacent to three populations of freeze-killed house fly pupae. Additional populations of freeze killed pupae were placed 5, 10, and 15 m from the three release locations in the four cardinal directions. After 4 wk, levels of parasitism ranged from 40 to 49% 15 m from the release point at all three locations. Hosts placed out 2 wk after the parasites were placed in the field were heavily parasitized after 1 wk of exposure, suggesting that parasites were still moving from the release point or that the parasites were remaining at the sites of host exposure. Hosts placed out 4 wk after the releases had lower levels of parasitism than those exposed in weeks 0 and 2; this suggests that some of the parasites had left the area or had died. High levels of parasitism in hosts placed out in week 6 were attributed to parasitism by progeny of parasites initially released. The study suggests thatM. zaraptorreadily searches at least 15 m from a release point and parasitizes available hosts when encountered, and that when released in the center of a pen, movement away from release point is essentially uniform, at least over short distances.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1155

出版商:Oxford University Press    

年代:1991

数据来源: OUP

摘要:

Anastrepha ludens(Loew) developmental time and egg clutch size were determined in grapefruit (Citrus paradisiMad.), orange (Citrus sinensisOsbeck), mango (Mangifera indicaL.), and peach (Prunus persicaL.), and the suitability of citrus was determined forA. ludensdevelopment to adulthood in the laboratory. Developmental time for immature stages ofA. ludensvaried with host fruit species. Egg incubation required 3.8, 4.3, 4.6, and 3.8 d, and larvae developed in 27.4, 29.7, 22.3, and 10.3 d in grapefruit, orange, mango, and peach, respectively. Pupae developed in 17.1, 13.7, 14.2, and 13.0 d in the fruit mentioned above, respectively. Larger egg clutches were oviposited in peach than in the other tested fruit. Suitability of citrus for development ofA. ludensimmatures varied with fruit species and varieties. ‘Marsh’ and ‘Ruby Red’ grapefruit were more suitable forA. ludensimmatures development than ‘Valencia’ orange. Peach susceptibility toA. ludensincreased as the ripening process advanced. The egg clutch size and development of immatureA. ludensare thought to be related to pulp compactness, albedo thickness in citrus, and resistance of rind to penetration.

ISSN:0046-225X    

DOI:10.1093/ee/20.4.1160

出版商:Oxford University Press    

年代:1991

数据来源: OUP