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The effects of plant age and infestation level of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), on visible plant damage, and the effect of plant age on spider mite population growth on impatiens, Impatiens wallerana Hook.f. (Ericales: Balsaminaceae), were determined by inoculating impatiens plants of three different ages with two densities of spider mites. Each plant was inoculated with either one adult female mite per three leaves or six leaves based on the average number of leaves on plants of each of the three age classes. Subsequently, leaf damage was correlated with mite-days (cumulative spider mite density) per leaf. The results showed that older aged plants exhibited greater damage than younger plants. Regression models of damage thresholds for each plant age suggest that monitoring for spider mites must be done periodically throughout the entire plant production cycle, but that more attention should be given toward the end of the cycle. Measurements of visible leaf damage were correlated with plant marketability. Specifically, the level of damage (proportion of damaged leaves per plant) at which plant marketability changes from a “premium” to a “discounted” category was 0.04–0.06. Thus, regression equations of the damage threshold could be used to estimate a cumulative spider mite density or mite-days equivalent to the economic threshold. Based on these equations, 5% leaf damage corresponds to 2.1, 1.51, and 1.25 mite-days for youngest, intermediate, and oldest plants, respectively. Because the damage threshold on impatiens was shown to be very low, the action threshold for biological control is essentially zero, and predators would need to be released as soon as damage is observed.

Diatomaceous earth (DE) can be used as a surface treatment in stored wheat Triticum aestivum (L.) to control pest infestations. However, it is not known how the thickness of the DE-treated wheat layer or grain temperature impact effectiveness. Therefore, we conducted an experiment in growth chambers to assess the effect of different surface layers of hard winter wheat combined with DE on spatial distribution, adult survival, and progeny production of lesser grain borer, Rhyzopertha dominica (F.), and to determine whether temperature and exposure interval modified this effect. When adult lesser grain borers were released in experimental towers containing untreated wheat or wheat admixed with DE to a surface layer depth of 15.2, 22.9, or 30.5 cm, they were able to penetrate all DE layers and oviposit in the untreated wheat below. However, survival was significantly reduced in adults exposed to DE. Survival decreased both with increasing depth of the DE-treated wheat and with exposure interval. Temperature had no effect on adult survival, but significantly more progeny were produced at 32 than at 27°C. Progeny production was inversely correlated with the depth of the DE-treated layer. Vertical distribution patterns of parental beetles were not significantly different among treatments or exposure intervals; however, more insects were found at greater depths at 32 than at 27°C. The F1 production was reduced by 22% at the thickest DE-treated layer. However, we conclude that this level of survival could leave a residual population of lesser grain borers that would probably be above an allowable threshold for insect damage.

The twospotted spider mite, Tetranychus urticae Koch, is an important pest of impatiens, a floricultural crop of increasing economic importance in the United States. The large amount of foliage on individual impatiens plants, the small size of mites, and their ability to quickly build high populations make a reliable sampling method essential when developing a pest management program. In our study, we were particularly interested in using spider mite counts as a basis for releasing biological control agents. The within-plant distribution of mites was established in greenhouse experiments and these data were used to identify the sampling unit. Leaves were divided into three zones according to location on the plant: inner, intermediate, and other. On average, 40, 33, and 27% of the leaves belonged to the inner, intermediate, and other leaf zones, respectively. However, because 60% of the mites consistently were found on the intermediate leaves, intermediate leaves were chosen as the sampling unit. These results lead to the development of a presence–absence sampling method for T. urticae by using Taylor coefficients generic for this pest. The accuracy of this method was verified against an independent data set. By determining numerical or binomial sample sizes for consistently estimating twospotted spider mite populations, growers will now be able to determine the number of predatory mites that should be released to control twospotted spider mites on impatiens.

The twospotted spider mite, Tetranychus urticae Koch, is an important pest of ivy geranium and other ornamental plants. As a part of our long-term goal to develop an integrated crop management program for ivy geraniums, the focus of this study was to produce a reliable sampling method for T. urticae on this bedding plant. Within-plant mite distribution data from a greenhouse experiment were used to identify the young-fully-opened leaf as the sampling unit. We found that 53% of the mites on a plant are on the young-fully-opened leaves. On average 22, 37, and 41% of the leaves belonged to the young, young-fully-opened, and old leaf categories, respectively. We then developed a presence-absence sampling method for T. urticae in ivy geranium using generic Taylor's coefficients for this pest. We found the optimal binomial sample sizes for estimating populations of T. urticae at densities of between 0 and 3 mites/leaf to be quite large; therefore, we recommend the use of numerical sampling within this range of T. urticae densities. We also suggest that population estimates of T. urticae on ivy geranium be done based on mite density/unit area of greenhouse space, both for conventional greenhouse pest management, and for determining how many phytoseid predators to release when using biological control.

Field releases of the indigenous egg parasitoid Crayon pennsylvanicum (Ashmead) resulted in a 4-fold reduction in squash bug, Anasa tristis (De Geer), densities on ‘Jack-O-Lantern’ pumpkins in 1991. However, pest populations subjected to parasitoids were consistently higher, and fruit yields and quality lower, than on plants that were treated with the insecticide, esfenvalerate, When the squash bug-resistant ‘Green-Striped Cushaw’ was used, the difference in pest densities on parasitoid-released and insecticide-treated plants was only half of that observed on the susceptible cultivar. In 1992, under abnormally wet, cool conditions, squash bug densities were higher on insecticide-treated plants and lower on plants where parasitoids were released than in 1991. Fruit quality for both cultivars was substantially reduced in all treatments in 1992, The wet, cool conditions apparently had less of an effect on pest densities and fruit yields on resistant pumpkins than on susceptible pumpkins. The expected net income for insecticide-treated pumpkins was substantially lower in 1992 than in 1991. Where biological control and host plant resistance were combined, loss in expected net income in 1992 was considerably less than in 1991. Although costs associated with biological control were very high relative to the revenues, integrating biological control with host plant resistance may have some potential as an alternative management strategy.

Laboratory investigations of the gregarious squash bug egg parasitoids Ooencyrtus anasae (Ashmead) and O. sp. were conducted at 20.8, 23.0, and 26.6°C. Females of both species emerged with undeveloped ovaries. Oöcyte development proceeded during the preovipositional period (ca. 35 h at 26.6°C) but did not exceed half of the total fecundity at initial oviposition. Preovipositional periods, time to peak oviposition, and time to 75% oviposition were generally similar for both parasitoids at 20.8°C. However, reproductive responses differed at temperatures above 20.8°C. In O. anasae, oviposition occurred significantly earlier, and at a similarly higher rate, at 23.0 and 26.6°C than at 20.8°C, whereas significant changes in preovipositional and ovipositional biology of O. sp. occurred only after an increase from 23.0 to 26.6°C. O. sp. had a significantly higher fecundity and longer ovipositional period at each temperature than did O. anasae. Mean fecundities did not change significantly with increasing temperature. Both parasitoids had an unusually long postreproductive period (ca. 1 mo) and a longevity of 40 to 50 d. At 26.6°C, O. sp. had higher gross and net reproductive rates than O. anasae. However, O. anasae had a shorter generation time (21.4 versus 23.8 d) and higher innate capacity for increase (0.146 versus 0.134).

A laboratory experiment was conducted to determine whether leaf exudates could be used as a source of adult nutrition for the squash bug, Auasa tristis (De Geer), egg parasitoid, Gryon pennsylvanicum (Ashmead), and to compare adult and progeny fitness traits when female Wasps were provided with squash leaves, a standard honey diet, a combination of leaves and honey, or water only Results showed that fecundity, progeny developmental rates, and progeny survival did not differ significantly when females were exposed to different dietary sources. Adult longevity was shorter on squash leaves without honey than on leaves with honey or the honey–only diet. However, reproductive fitness was not reduced because oviposition had been completed before death of the adult females. When only water was provided, parasitoid females lived only a few days. Observations showed that squash leaves have two kinds of trichomes (hair–like and peg–like), both of which produce droplets that are fed on by both sexes of G. pennsylvanicum. Nutrient analyses revealed that exudates from the hair–like trichomes are composed predominantly of monosaccharides (mainly glucose and galactose), and that the peg–like trichomes produce glucose and some protein. Thus, these trichomes appear to serve as extrafloral nectaries and may provide an important energy source for augmentatively released G. pennsylvanicum.

Laboratory investigations of the gregarious squash bug egg parasitoids Ooencyrtus anasae and O. n. sp. near anasae (O. sp.) were conducted at 20.8, 23.0, and 26.6°C. In both species, total developmental periods (egg to eclosed adult) were inversely related to temperature. Temperature had no significant influence on survivorship, progeny production, or sex ratio. At each temperature, O. anasae developed and emerged about a day earlier and produced a significantly higher percentage of female progeny (77%) than did O. sp. (60%). Both parasitoids deposited an average of three (2–7) progeny per host. However, O. anasae consistently deposited more female eggs per host than did O. sp. Proportion of females produced per host by O. anasae tended to increase directly with number of hosts parasitized, but no such relationship was observed in O. sp. Total preimaginal survivorship in both parasitoids was about 89%. In O. sp., male progeny that developed without females emerged about a day later at all temperatures and had a lower pharate adult survivorship than did males that developed in hosts with female siblings.

Survivorship of the spherical mealybug, Nipaecoccus vastator (Maskell), was significantly higher on branches of Leucaena leucocephala (Lam.) De Wit. (Leguminosae) tended by the ant, Technomyrmex albipes F. Smith, than on branches from which ants were excluded. The presence of ants decreased the percentage of mealybugs parasitized by the encyrtid, Anagyrus indicus Shafee, Alam, and Agarwal (Hymenoptera), and the mortality attributable to host killing by A. indicus and predation by other arthropods. Because ant interference occurs at only a few isolated localities in Guam, our experiments support the hypothesis that natural enemies play an important role in maintaining mealybug populations at low levels.

Understanding the population dynamics and co-evolution of host–parasite systems requires detailed knowledge of their phenology which, in turn, requires a deep knowledge of the effect of abiotic factors on the life cycles of organisms. Temperature is known to be a key environmental influence that participates in the regulation of diapause. Yet, not much is known about the effect of temperature on the free-living stages of true parasites and how it may influence host–parasite interactions. Here we experimentally study the effect of ambient temperature on overwintering pupae of Carnus hemapterus (Diptera, Carnidae), an ectoparasitic fly of various bird species. We also test whether chilling is a prerequisite for completion of diapause in this species. In the course of three winter seasons we experimentally exposed carnid pupae from nests of various host species to spring temperatures with and without chilling and recorded the emergence patterns in experimental and control groups. Experimental groups showed an advanced emergence date, a lower emergence rate and, consequently, a protracted emergence period. Chilling had no obvious effect on the start of emergence but it did advance the mean emergence date, shortened the length of the emergence period when compared with the control treatment and increased the emergence rate when compared with the spring treatment. This study identifies an environmental cue, namely temperature during the free-living stage, affecting the emergence of a widespread parasite and demonstrates the plasticity of diapause in this parasite. Our findings are of potential significance in understanding host–parasite interactions. [ABSTRACT FROM AUTHOR]