The discontinuous gas exchange cycle (DGC) was described in the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae) for the first time. Also, the effect of the DGC on water loss was investigated. The CO2 emission pattern in both insecticide resistant and susceptible B. germanica varied with temperature. At 10, 15, and 20°C the pattern was discontinuous. Cycle frequency increased at 25 and 30°C, and at 35°C the pattern became cyclic. In most DGCs, there was no clear distinction between the closed and flutter phases in both strains thus data for these phases were combined and analyzed as the interburst phase. The probability that B. germanica would breath discontinuously varied with temperature. Most cockroaches (62.8%) displayed DGCs at 10°C, therefore measurement of metabolic rate and water loss was carried out at this temperature. Using repeated measures of analysis of variance, the interburst and burst V˙CO2(mlh-1) were not significantly different between the two strains. The variability in CO2 emission during the interburst and burst phases over time was not significantly different from cycle to cycle or between strains. Overall metabolic rate during the entire recording was not significantly different between both strains. There was a significant difference in the duration of the interburst and burst phases between the strains. The susceptible strain had significantly longer interburst and burst phase durations during a complete DGC than the resistant strain. The interburst and burst phase durations were 5.01±0.19 and 6.21±0.13min, respectively, for the resistant strain, whereas the durations were 7.16±0.37 and 6.73±0.17min, respectively, for the susceptible strain. This resulted in a DGC of significantly longer duration (13.89±0.44min) in the susceptible strain compared with the resistant strain (11.23±0.26min). The duration of the interburst phase was significantly different from the open phase duration in the resistant strain such that during a single DGC lasting ∼11.23min, 43.5% consisted of the interburst phase while the burst phase made up 56.5% of the cycle. The cuticular permeability at 10°C and 0% RH was 2.26μgcm−2h−1mmHg−1 for the resistant strain and 3.42μgcm−2h−1mmHg−1 for the susceptible strain. In both strains, cuticular transpiration accounted for ∼95% of total water loss. The significantly longer duration of the interburst phase of the susceptible strain was not important in reducing water loss.

Herbivorous insects often feed on pathogen-infected plants in nature, and it is likely that pathogen infection alters host plant quality. We documented the effects of plant infection by a widespread plant virus on host plant quality for a generalist insect herbivore and tested the hypothesis that these effects vary among plant genotypes. We found that infection by Cucumber mosaic virus (CMV) altered the host plant quality of Mimulus guttatus (Phrymaceae) for meadow spittlebugs, Philaenus spumarius (Hemiptera: Cercopidae). The effects of CMV infection on host plant quality, however, varied among full-sib M. guttatus families, suggesting that these effects vary among plant genotypes. In most full-sib families, CMV infection either had no effect on host plant quality or increased host plant quality as measured by spittlebug size and development time. In a few M. guttatus families, however, CMV infection decreased host plant quality. There was no relationship between the effect of CMV infection on plant growth and the subsequent effect of CMV infection on spittlebug performance, suggesting that broad changes in host plant performance (e.g., growth rate) were not responsible for the effects of CMV infection on host plant quality for spittlebugs. We suggest that future studies of the effects of pathogen infection of plants on insect herbivores consider variation among plant genotypes in the mechanisms and ecological consequences associated with these effects.

Inbreeding in the form of self-fertilization is widespread among plants and typically results in broad, detrimental changes in plant morphology and physiology. Phenotypic changes associated with inbreeding are likely to alter interactions between inbred plants and other organisms, but few studies have investigated this potential. We found that inbreeding in the entire-leaf morning glory, Ipomoea hederacea var. integriuscula, altered this plant's ability to resist and tolerate attack by insect herbivores. The effects of inbreeding on plant defense, however, varied among insect species, and plant defense theory helped explain this variation. If the effects of inbreeding on plant phenotype are analogous to those of environmental stresses, then the plant vigor hypothesis predicts specialist herbivores will perform better on outbred plants, and the plant stress hypothesis predicts that generalist herbivores will perform better on inbred plants. We conducted a series of greenhouse experiments in which we reared...

Inbreeding, which is common in plants, may increase the vulnerability of. populations to natural enemies. Similarly, natural enemies may increase the expression of inbreeding depression in their hosts, resulting in altered selection on host mating-system evolution. To examine effects of inbreeding on tolerance to herbivory, we transplanted experimentally self- and cross-fertilized plants into four field populations of Mimulus guttatus and applied single Philaenus spumarius (spittlebug) nymphs to half. At the end of the growing season, we scored plants for five fitness components (reproductive effort, biomass, survival, probability of producing flowers or buds, and probability of bolting). Inbreeding reduced population-level tolerance to spittlebug herbivory with respect to plant aboveground biomass. Inbreeding effects on tolerance varied significantly among plant families for three fitness traits, indicating the opportunity for selection by herbivores to improve tolerance in in breeding populations. These results also indicate that herbivores can alter inbreeding depression in plants. Our results mirror earlier greenhouse studies of inbreeding effects on plant-herbivore interactions, and demonstrate that these effects can be manifested in natural settings as well. This study indicates that inbreeding in natural populations can affect fitness not only directly, but also indirectly through altered interactions with natural enemies.

Red imported fire ants, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), are an invasive species found in high densities throughout southeastern agricultural systems. We tested the hypothesis that fire ants tend cotton aphids, Aphis gossypii Glover (Homoptera: Aphididae), and thus release them from predation by lady beetle larvae, Coccinella septempunctata L. and Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae), and green lacewing larvae, Chrysoperla carna Stephens (Neuroptera: Chrysopidae). Fire ants preferentially foraged on aphid-infested cotton, Gossypium hirsutum L., plants ((x) over bar = 103 +/- 47 ants per plant) compared with plants without aphids ((x) over bar = 5 +/- 3 ants per plant). In caged greenhouse experiments, fire ants reduced survival of lady beetle larvae by 92.9% and green lacewing larvae by 83.3%. Furthermore, strong mortality imposed on aphid predators by fire ants affected aphid survival. With the addition of fire ants to aphid-predator treatments, aphid survival approximately doubled. In a field experiment, predator larvae were more abundant in cotton plots with experimentally suppressed densities of fire ants (0.62 +/- 0.11 lady beetle larvae per sample; 0.06 +/- 0.02 lacewing larvae per sample) than in plots with high fire ant densities (0.23 +/- 0.06 lady beetle larvae per sample; 0.01 +/- 0.01 lacewing larvae per sample). Conversely, cotton aphids were more abundant in high fire ant density field plots ((x) over bar = 6.83 +/- 0.03 aphids per leaf) than in low fire ant density plots ((x) over bar = 4.04 +/- 0.03 aphids per leaf). These data suggest that red imported fire ants enhance cotton aphid survival and density in the field through predator interference.

Host shifts and subsequent host-race formation likely play a more common role in the speciation of herbivorous insects than has generally been recognized. Our studies of the interactions of goldenrod host plants (Solidago Compositae), the gall fly Eurosta solidaginis (Diptera: Tephritidae), and the stem- and gall-boring Mordellistena convicta (Coleoptera: Mordellidae) provide behavioral, ecological, and genetic evidence of insect host races that may represent incipient species formed via sympatric speciation. Eurosta solidaginis has developed genetically differentiated and reproductively isolated host races that are associated with the ancestral host Solidago altissima and the derived host S. gigantea. Conventional wisdom suggests that shifts even to closely related host plants are limited by host preferences or the inability to utilize a chemically and developmentally distinct host. However, our preliminary work with Eurosta from S. gigantea implies that host choice and gall induction do not deter a shift to S. canadensis. The galling of Solidago by Eurosta created a new resource that has led to a subsequent host range expansion by the stem-boring beetle. Mordellistena convicta from stems and galls are genetically distinct and likely shifted from stems to galls. Beetles from S. altissima versus S. gigantea galls exhibit assortative mating and higher preference for and/or performance on their natal host. The present-day distributions of the Eurosta host races and their behavioral isolating mechanisms do not suggest that geographic isolation was required for their formation; rather these characteristics suggest a sympatric mode of differentiation. Our findings lend credence to recent assertions that sympatric speciation may be an important source of biodiversity.

The fife history and habitat preference of the wolf spider Gladicosa pulchra were investigated in several populations in Mississippi. Gladicosa pulchra has a one year life cycle with spiders changing from forest floor to tree trunk habitats in late summer or early fall. During the fall, spiders were found almost exclusively on trees (93% of observed spiders in 1989 and 80% of observed spiders in 1990). Males were observed to inhabit trees earlier in the year than females. Spiders did not climb trees smaller than 2 cm in diameter at breast height. Most individuals were collected at heights less than 2.5 m, and spiders were primarily oriented face down while on trees. The role that environmental factors play in this animal's habitat preference is discussed.