In the quantitative analysis of experimental data regarding temperature-dependent development, the so-called law of total effective temperature is sometimes expressed in the linearized ^{equation 1,}: 1/D = −(t/k) (1/k)T. D indicates the duration of development; T, temperature; t, the estimated developmental zero temperature; and k, the effective cumulative temperature. The method of fitting usually involves the regression of y = 1/D on x = T. Although the degree of fitting of ^{equation 1,} to data within optimum temperature ranges is fairly satisfactory, we have in the current study addressed three problems regarding the use of ^{equation 1,} and methods of fitting involving the regression of y on x. First, we found that the detection of optimum temperature ranges is frequently difficult with ^{equation 1,}. Second, in applying the method of regression of y on x with ^{equation 1}, the weights of the data points are disproportionate between those in the upper and lower parts of the line and they are not homogeneous along the temperature axis. The lower the temperature, the more disproportionate weight is burdened and the less weight is loaded. Third, in most of the data, errors in the x-variable are ignored. The second and third problems would in most cases result in a reduction in the slope of the line, a smaller t, and a larger k. Therefore, we proposed a new linearized formula: (DT) = k tD. We further propose the use of the reduced major axis, obtained as the solution of the functional model among bivariate errors-in-variables models, in the method of fitting to data. We demonstrated that the majority of the problems raised above could be unraveled under this new approach based on statistical analysis.

An organophosphate/pyrethroid resistant strain of the phytoseiid mite Typhlodromus pyri Scheuten was imported from New Zealand in 1988 for use in biological control of European red mite, Panonychus ulmi (Koch), and apple rust mite, Aculus schlechtendali (Nalepa), in Nova Scotia. To better understand the overwintering strategy of T. pyri and the likelihood the New Zealand strain would withstand winter conditions in Canada, we measured supercooling points and mortality of diapausing females held at subzero temperatures. Mites in quartz crucibles were placed in the liquid nitrogen-cooled stage of a cryostage microscope, and temperature was lowered 1°C/min until the mites froze, as indicated by an instantaneous darkening of their body contents. Supercooling points of the New Zealand strain averaged −18.2°C for July to September, were −23.2°C in October, and averaged −28.2°C in the colder months from November to March. The mean supercooling points for December 1994 did not differ from the mean for the native Nova Scotian strain. However, the mean supercooling point of the New Zealand strain for March 1995 was higher than the means for the native strain and for a T. pyri strain that was imported from Geneva, NY. New Zealand strain T. pyri taken from cloth bands affixed to orchard trees were placed on apple leaves in plastic vials and exposed to low temperatures for various periods of exposure. At −5°C, mortality at 24 h was less for mites collected in February than for those collected in November (6% versus 44%) but at −10°C trends were similar, reaching 100% by 24 h in both trials. For the February trial, a logistic function with a coefficient for the product of time and temperature explained 61% of the variation in mortality. If these results are applied to populations in Nova Scotian orchards, where winter temperatures of −10°C are common, one would predict complete annihilation of the New Zealand strain. However, populations of the New Zealand strain, first released in orchards in 1988, have survived every winter since that date and have proven effective in biological control of European red mite and apple rust mite. Possible reasons for survival and increase of populations of this exotic strain of T. pyri, despite apparent susceptibility to cold-induced mortality, are discussed.

The effect of the tomato (Lycopersicon esculentum Miller) resistance gene, Mi, on the feeding behavior of the potato aphid, Macrosiphum euphorbiae (Thomas), was studied using an AC electronic monitoring system. Aphids were monitored for at least 16 h on nearly isogenic tomato lines, and we observed waveforms corresponding to the stylet pathway phase, sieve element and nonphloem phase. The time to the first probe was not significantly different between resistant and susceptible tomato lines, indicating that leaf surface components were not involved in the resistance. Also, time to the first sieve element contact, as indicated by the sieve element phase waveform, was not significantly different, indicating that aphids were able to locate the sieve element equally well on resistant and susceptible lines. However, the duration of the sieve element phase was 7- to 10-fold longer on susceptible plants than on resistant plants. The insect also made more frequent and briefer probes on resistant tomato than on susceptible tomato. These results indicate that the mechanism of resistance mediated by Mi involves limitation of the duration of the sieve element phase, and salivation and ingestion of phloem fluids associated with it.

This study addresses four hypotheses that may account for differences in the number of insect herbivore species among plant species. These hypotheses are based on the assumption that insect diversity is a function of the number, quantity, and distribution of plant resources used by herbivores. The study investigated predictions that herbivore species richness will increase as a function of increasing the following: (1) host plant distribution over the landscape (host plant geographical distribution hypothesis), (2) host plant density within a habitat (resource concentration hypothesis), (3) size of individual plants (plant size hypothesis), or (4) abundance of resources (resource abundance hypothesis). We tested predictions from these hypotheses by examining the species richness of insect herbivores on five sympatric species of fabaceous plants that varied in their local dispersion of individual plants and plant architecture. Among these five species, plant geographical distribution varied threefold, density varied 38-fold, plant size and food resources available to insect herbivores varied ≈100-fold. Plant geographical distribution, plant size, and the resource concentration hypotheses were not corroborated in this study. Resource abundance, measured as plant dry weight, accounted for the differences in number and abundance of insect species between host plant species. Leaf biomass accounted for 44.15% of the variation in number of insect herbivore species and 51.76% of the variation in abundance of insect herbivores using leaves as resources. Flower biomass accounted for 32.86% of the variation in the number of insect herbivore species using flowers. Therefore, plants that offered a greater quantity of resources, especially leaves and flowers, had greater species richness and abundance in insect herbivores.

Laboratory experiments using small artificial streams were performed on 3rd–5th instars of the net-spinning caddisflies Hydropsyche sparna (Ross), H. betteni Ross, H. morosa (Hagen), and H. slossonae (Banks) to examine behavioral responses after exposure to sand particles ranging from 126 to 2,000 μm in diameter. Sediment loads up to 14.6 kg/m² were applied. When buried, the insects drifted, died, or remained “buried-alive.” When buried-alive, the larva remained in contact with its retreat and extended head, thorax, and anterior abdomen into the overlying water. Drift predominated when particle diameters were below 1,000 μm. Larger particles induced the buried-alive behavior. Mortality rates varied from 0 to 4.8%. Behavioral response to deposited sediment was similar in 3rd, 4th, and 5th instars. Larvae of H. betteni, H. morosa, and H. slossonae exhibited similar behaviors to H. sparna. The buried-alive behavior may represent an adaptation to frequent exposure to bedload sediment transport. Bedload sediment transport of the duration and magnitude studied is either a lethal or a sublethal disturbance, depending on the sediment particle size.

The threshold temperature for postdiapause development in overwintering eggs of the European red mite, Panonychus ulmi (Koch), was determined after exposing the eggs to various constant temperatures (5, 10, 15, 20, and 25°C) in the laboratory. The mean number of days to 50% hatch in each temperature was >120, 44.5, 22.0, 14.5, and 8.1 d, respectively. From the regression of postdiapause developmental rate to temperature, it was estimated that 50% of egg hatch coincides with the accumulation of 154.6 degree-days (DD) above the threshold of 7.4°C. In the field (1991 and 1993–1996), 50% egg hatch occurred from the end of March to 20 April after the accumulation of a mean sum of 129.4 ± 4.5 DD above the threshold of 7.4°C from 10 February onward. The starting date of 10 February for heat accumulation was chosen because earlier experiments had shown that diapause is terminated in 50% of the eggs in the first half of February. Using the theoretical sum of 154.6 DD, the predicted dates for 50% egg hatch deviated from field observations by an average of 3.7 ± 0.5 d over the 5 yr of experiments.

A field-based experimental study examined the roles of temperature and moisture in the dry-season embryonic dormancy and postdormancy hatching of the spittlebug Deois flavopicta Stål from Brazil’s dry interior region. The results show that dormancy consists of two discrete parts: an initial period of diapause that persists from April to the beginning of July, followed by a period of postdiapause quiescence that prevails until the rainy season begins (usually October). Low temperatures during the early part of the diapause period accelerates diapause development, whereas contact with liquid water determines the timing of postdiapause hatching. Soil temperatures during June and July and the relative humidity of the soil during August and September strongly affect overwintering survival and thus are important in determining the size of the nymphal population after dormancy. The findings indicate that, like hibernation and aestivation in temperate-zone insects, dry-season dormancy in tropical insects is a dynamic state that is influenced by seasonal changes in key environmental factors.

We studied the importance of vision and antennal olfaction in the location of habitat, prey patches within habitats, and the close-range orientation to prey for three common predatory heteropterans [Nabicula subcoleoptrata (Kirby), Nabis americoferus Carayon, and Sinea diadema (F.)]. In each of the experiments, predators were randomly assigned to no vision (eyes painted), no antennal olfaction (antennectomy), or control treatment groups. Habitat location by two of the predators (Nabicula subcoleoptrata and S. diadema) was compared among the treatments in a field study. Antennal olfaction was critical in habitat location for both species, but as release distance increased, fewer bugs in all treatment groups located the habitat. Similarly, all three species relied on antennal olfaction for prey patch and close-range orientation to prey [Lygus lineolaris (Palisot de Beauvios)]. In a greenhouse experiment, individuals with antennae intact were aroused to prey up to 30 cm away more often (60%) than were antennectomized bugs (20%). In other studies, antennectomized bugs captured fewer prey than control or blinded individuals, but a few individuals lacking both vision and antennal olfaction located prey, suggesting the use of additional cues such as prey-created vibration. Assuming that chewing prey create more vibration than do sucking prey positioned in feeding sites, we compared the number of chewing (Colias eurytheme Boisduval larvae) and sucking (L. lineolaris nymphs) prey taken by the three predators. Although vibration alone did not appear to facilitate prey location for any of the predators, vibratory signals were used in addition to olfactory cues by Nabis americoferus.

We examined the relative importance of vision and antennal olfaction in enemy avoidance by three heteropterans. Jumping spiders (Phidippus spp.) served as enemies of Nabicula subcoleoptrata (Kirby) and Nabis americoferus Carayon, and praying mantids (Tenodera aridifolia sinensis Saussure) were used as enemies of Sinea diadema (F.). In a greenhouse study, the number of bugs surviving enclosure with spiders or mantids was compared among individuals without vision, without antennal olfaction and controls after 0.5, 1, 4, and 24 h. For Nabicula subcoleoptrata and S. diadema, vision appeared to be of primary importance in avoiding capture by enemies. In contrast, most Nabis americoferus were killed by spiders and no significant difference in survival existed among the treatment groups. The importance of vision in predator avoidance is in contrast with a recently documented reliance on antennal olfaction for prey location in these species. Thus, stimuli from prey and predators may be segregated to maximize the efficiency of sensory information processing.

Development, imaginal survivorship, adult longevity and fecundity of the predatory phytoseiid mite Euseius (Amblyseius) finlandicus Oudemans reared on seven different plant pollens were determined in the laboratory. The rationale behind these experiments was to assess the nutritional value and the possible effect on development and population dynamics of the mite. Mites were kept individually on bean (Phaseolus vulgaris L.) leaf disks at 20 ± 1°C and a photoperiod of 16:8 (L:D) h, with a sufficient quantity of pollen of apple (Malus silvestris M.), pear (Pyrus communis L.), cherry (Prunus avium L.), peach (Prunus persica L.), apricot (Prunus armeniaca L.), walnut (Juglans regia L.), or poppy (Papaver rhoeas L.). Developmental time from neonate larva to adult emergence varied between the different pollens from 6.03 to 6.62 d for females and from 5.46 to 6.14 d for males. Survivorship during immature development varied from 67.2 to 95.9% with the lowest value recorded on peach pollen. The average life span of adult females reared on the different pollens varied from 18.2 to 56.2 d, whereas the respective total fecundity ranged from 2.5 to 46.5 eggs per female. The estimated values of the intrinsic rate of increase (r_m) varied from 0.012 to 0.150. The analysis of these results show that cherry, peach, apricot, walnut, and poppy pollens are of higher nutritional value for E. finlandicus than apple and pear pollens and thus may play an important role in the field for sustaining and increasing the predator’s population.

We studied the movement and feeding behavior of nymphs of the grass feeding spittlebug Deois flavopicta Stål to evaluate the role of host plant species on the spatial distribution of the nymphs. The inter- and intraplant foraging patterns of the nymphs contributed to their patchy distributions. The young nymphs, despite their weak motility, moved from the hatching spot and chose feeding sites. They tend to move less when host plants were present. Plant quality near hatching sites influenced the movement pattern of newly hatched nymphs. Egg densities at the oviposition sites did not influence the movement of newly hatched nymphs. The distribution of nymphs in relation to differences in host species and shoot age of host plant was studied in the field and in multiple choice experiments. Both young and old nymphs preferred plants of the introduced host in the genus Brachiaria over the native grass Axonopus marginatus (Trinius) Chase. The nymphs fed gregariously on buds and young shoots as first and second instars and in small groups of third, fourth, and fifth instars on old shoots of different sizes. These patterns of attack may be related to differences in tissue hardness or amino acid content between young and old shoots, and between host species. Nymphal survivorship was higher on B. ruziziensis, the preferred host plant. In addition, survivorship of newly hatched nymphs was higher on young buds and shoots compared with old shoots. The possible consequences of nymphal feeding behavior on population dynamics are discussed.

Temperature-dependent development of strawberry root weevil, Otiorhynchus ovatus (L.), pupae was studied in strawberry (Fragaria × ananassa Duch. variety ‘Totem’). The development of pupae was investigated at constant temperatures from 3 to 33°C at 3°C intervals. The upper thermal lethal limit for strawberry root weevil pupae was between 30 and 33°C. Pupae did not eclose below 6°C. Pupal duration was 127 d at 6°C and 7 d at 30°C. Rate of development (1/d) was greatest at 30°C. We used the development of strawberry root weevil as a model system to suggest a modification on the traditional method of creating linear degree-day models. This method used weighted regression and was based on the assumption that the purpose of creating prediction models is to model the development of insects based on the temperatures to which they are exposed in the field. The predictive ability of this weighted model was compared with a traditional nonweighted linear degree-day model by relating predictions to the observed occurrence of strawberry root weevil lifestages determined by field sampling. The weighted linear pupal prediction model produced a developmental threshold of 4.3°C and a degree-day requirement of 227.3. The nonweighted linear pupal prediction model produced a developmental threshold of 6.2°C and a degree-day requirement of 163.9. Using a weighting method maintains the utility of a linear model while allowing for more accurate estimate of the lower developmental threshold.

The physiological development time was determined for the immature stages of summer form codling moth, Cydia pomonella (L.), when reared at both constant and field-simulated temperatures. The phenological data thus obtained was used to examine the zero temperature threshold to model codling moth development. Two procedures were used to determine the base or zero development temperature for codling moth. They were the x-intercept, i.e., an extrapolation of the best-fit linear approximation of the reciprocal of time for development (days or hours) at each of a series of constant temperatures; and second using thermal units, i.e., physiological development time (degree-hours). The thermal unit was a constant at any logical rearing temperature when using the correct base (zero development) temperature. Physiological development time became increasingly curvilinear as the base temperature deviated from the correct value. Errors in base temperature, particularly at lower temperatures, introduce large errors into phenology models, reducing their reliability when used to time pest management procedures. Thermal units may be used to directly determine the base temperature or to validate the precision of the x-intercept. When reared at constant temperature, mean development time was 2,100, 6,100, and 5,800 degree-hours, but when reared under field-simulated (variable) temperatures the mean development time was reduced by 0, 500, and 1,100 degree-hours for eggs, larvae, and pupae, respectively. Development was retarded at 35°C when reared at constant temperature, but not when reared at field-simulated temperatures that were as high as 35°C for a few hours each day. There was no evidence for an upper temperature threshold using field-simulated temperatures. Modeling codling moth development in the field using field-simulated temperature data more accurately represents true development time. Fifteen percent of the larvae reared under long-daylength at 14.8°C entered diapause; whereas, there was no diapause at higher temperatures. Diapause induction at low temperature under long-daylength has not been previously reported.

Seven accessions or varieties of cultivated pea Pisum sativum L. varying in surface waxbloom characteristics were grown in replicated small plots (1 m²) for two seasons to monitor natural infestations of insect herbivores and abundance of predatory insects. Waxbloom was quantified on the basis of the amount of waxes extractable from leaf surfaces, densities of wax crystals visible with scanning electron microscopy, and visual appearance. During each season, pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphidae), densities per plant were significantly lower on peas with reduced surface waxbloom as compared with peas with standard or ‘normal’ surface waxbloom. This difference was greatest between two near-isolines of peas differing in expression of a mutation that reduces surface waxes. Although reduced-waxbloom plants had lower end-of-season above ground biomass and vine lengths, including these variables as covariates did not affect the significance of the waxbloom effects on aphid densities. Damage to leaves and stipules by the pea leaf weevil Sitona lineatus (L.) (Coleoptera: Curculionidae) was greater on reduced-waxbloom peas than normal-waxbloom peas. Thus, as occurs in other crops, reduced waxbloom in peas is associated with lower natural infestations of an aphid, but also with increased susceptibility to a folivorous beetle. Populations of predatory coccinellids did not differ consistently between years on reduced-waxbloom versus normal-waxbloom peas, failing to support a hypothesis that predator populations are higher on reduced waxbloom peas, contributing to the lower aphid populations on these plants.

Elevated atmospheric CO₂ concentrations will cause plants to grow faster, lower nitrogen content per unit of plant tissue, and generate higher carbon to nitrogen (C/N) ratios. We hypothesize that production of transgenic proteins will be reduced, thus reducing the efficiency of Bacillus thuringiensis (Bt) transgenes against insect populations. Commercially available transgenic cotton plants expressing the Cry 1Ac gene from Bt were compared with a near isogenic non-Bt cotton line in a split-plot design with two levels of atmospheric CO₂ (ambient, 370 ppm and elevated, 900 ppm) incorporating a 2 × 2 factorial design with two nitrogen (N) fertilization regimes (low, 30 mg N/kg soil/wk and high, 130 mg N/kg soil/wk), and two levels of Bt (presence or absence). Bioassays using Spodoptera exigua (Hübner) and quantitative enzyme-linked immunosorbent assays for toxin content indicated reduced Bt protein production in elevated CO₂. The tendency for test insects to consume more foliage from plants with lower N, caused by the elevated CO₂, did not compensate for the reduction in toxin production. N fertilization regime interacted with CO₂ concentration, showing that plants growing in N limited systems would produce substantially less toxin. The use of transgenic plants is becoming increasingly important and will continue to be so in the next decades. At the same time, atmospheric CO₂ increase will affect the effectiveness of this strategy. These observations have implications not only for agricultural use of transgenic plants, but also for the ecological consequences of transfer of Bt toxins to closely related wild plant genotypes.

Seasonal studies on a 1,200-ha isolated infestation of Solenopsis invicta Buren located in McMinn County, TN, were initiated in 1993 and continued through 1997. Winter survivability was evaluated and compared with a southern Mississippi site. The impact of S. invicta on local myrmecofauna was compared with a Tennessee non-infested site. Data collected over four winters indicate that consecutive days at a low ambient air maximum temperature is more indicative of S. invicta winter survivability than minimum temperature. After significant S. invicta mortality the first winter (1993–1994), we did not find significant differences in ant species diversity between the S. invicta infested Tennessee site and a similar, but non-infested site, 32 km away. Species commonly collected in the S. invicta infested site included Forelius pruinosus Roger, an unnamed Forelius sp., Paratrechina terricola (Buckley) and Pheidole vinelandica Forel.

Fine nylon mesh fences (135 cm high) with varying lengths of downward-sloping collection overhangs were evaluated for efficacy in excluding the female cabbage flies Delia radicum (L.) from plots of radish, Raphanus sativus (L.). During three trials conducted in 1994 and 1995, fences without overhangs, fences with 12.5-cm overhangs, or fences with 50-cm overhangs were tested against fences with standard 25-cm overhangs and unfenced control plots. In fenced plots with standard 25-cm overhangs, the mean number of D. radicum females caught on yellow sticky traps placed within plots was 85% less than those caught in corresponding control plots. The mean numbers of D. radicum females caught in fenced enclosures with no overhangs, 12.5-cm overhangs, or 50-cm overhangs, were 61, 67, and 94% less than those caught in corresponding control plots, respectively. The mean proportion of radishes damaged by D. radicum larvae inside enclosures with 25-cm overhangs was 62% less than in corresponding control plots. The mean proportions of radishes damaged inside fences with no overhangs, 12.5-cm overhangs, or 50-cm overhangs were 33, 59, and 81% less than those caught in corresponding control plots, respectively. Results are discussed in terms of defining an appropriate fence design for commercial use.

Survival of overwintering bean leaf beetle, Cerotoma trifurcata (Förster), populations in woodland and soybean habitats was studied for three consecutive winters from 1996 through 1999. Four locations of soybean fields and three locations of woodlands were studied at Iowa State University farms near Ames, IA. In the winter of 1996–1997, woodlands and soybean fields were sampled monthly from mid-November through mid-April of the following year, whereas in the winters of 1997–1998 and 1998–1999, both habitats were sampled twice a month from mid-October through mid-April. On each sampling date, three sampling units (1 m²) of leaf litter or crop residue was randomly collected from soybean fields and woodlands at each location. The collected samples were bagged and returned to the laboratory for estimates of overwintering beetles. The beetles obtained from the samples were kept in individual sample bags at 24°C for 100 h to assess their survival. The beetles were then kept in a freezer at −15°C for investigation of potential fungal pathogens and ectoparasitic mites. During the three-winter study, the mortality of overwintering beetles in soybean fields (77.04–88.89%) was higher than those in woodlands (48.9–82.29%). The effects of winter temperature on beetle mortality and a predictive model for the overwintering beetle survivorship are discussed.

Paired trap lines of five boll weevil pheromone traps each were placed on opposite sides of a brush line at six different sites on a plantation in the Lower Rio Grande Valley of Texas. Temperature, wind speed, and wind direction were monitored with a nearby weather station. We observed a strong negative relationship between mean daily wind speed and total daily capture of boll weevils. About half of the day-to-day variation in weevil captures was explained by wind speed alone. In addition, our data indicate that much of the variation between traps within days may arise from differences in local wind speed as governed by local vegetation depending on wind direction. Brush lines in this study slowed the wind by 40–70% and mitigated its effects such that traps on the leeward side averaged 2.5–2.9 times higher captures than traps on the windward side. The magnitude of the effect of windward or leeward placement of traps on weevil captures depended on the relative strength of the wind. Under light winds (<10 km/h), there were no increases in leeward trap captures. However, on days of moderate (10–20 km/h) or strong (>20 km/h) winds, leeward trap captures averaged 3.9- or 2.4 times greater than windward captures, respectively. By accounting for the ability of vegetation to dampen the effects of wind on boll weevil trap captures, we should be able to dampen daily and positional variation in trap captures by more careful placement of traps. Furthermore, judicious placement of traps in locations protected from prevailing winds should improve detection efficiency in areas where early warning of weevil presence is critical, such as in eradication and posteradication zones.

Field surveys were conducted on cowpea and pigeon pea in 1995 and 1996 to assess the effect of indigenous egg parasitoids on populations of Clavigralla tomentosicollis Stål in northern Nigeria. From the egg masses of C. tomentosicollis, three species of Hymenoptera belonging to three families, namel Anastatus sp. (Eupelmidae), Ooencyrtus utetheisae (Risbec) (Encyrtidae), and Gryon fulviventris (Crawford) (Scelionidae), were recorded. Among them, G. fulviventris was found to be the most abundant parasitoid. Of a total of 3,502 egg masses collected on cowpea from four geographical locations, 2,587 (73.9%) were found to contain at least one egg parasitized by G. fulviventris. From 56,072 eggs discovered, it parasitized 38,935 (69.4%). Overall, 74,724 eggs were collected from the four different locations and of these 52% were parasitized by G. fulviventris. However, parasitism rates varied with time and location. At one of the study sites (Minjibir, Kano) where weekly samples were collected throughout the growing season, the discovery efficiency, exploitation efficiency, and overall percentage parasitism increased significantly from July to November. Also, the proportion of eggs parasitized was found to be inversely related to the size of the egg mass. These findings are discussed in relation to the potential contribution of biological control in the integrated pest management of this economically important pest.

A series of field trials evaluated the efficacy of the entomopathogenic nematode, Steinernema carpocapsae Weiser All strain for control of western corn rootworm, Diabrotica virgifera virgifera LeConte, larvae. Separate trials examined the effects of nematode application rate and timing on corn rootworm control in 1991. In the rate trial, S. carpocapsae (0, 10⁴, 10⁵, 10⁶, and 10⁷ nematodes per 30.5 row-cm) was applied as the insect population entered the second instar. Nematode treatment significantly reduced corn root injury and adult emergence. High application rates (10⁶ and 10⁷ nematodes per 30.5 row-cm) significantly outperformed low rates (10⁴ and 10⁵ nematodes per 30.5 row-cm). Nematode treatment (500,000 S. carpocapsae per 30.5 row-cm) reduced root injury and adult emergence slightly in the timing trial; later applications (second, third instar) were numerically, but not significantly, more effective than early (egg, first instar) ones. In 1992, a factorial trial combined four application dates (egg; first, second, third instar) and five rates (0, 10⁴, 10⁵, 10⁶, 10⁷ S. carpocapsae per 30.5 row-cm). Later applications (second, and particularly, third instar) were significantly more effective than early (egg, first instar) ones. Root injury and adult emergence in control and low rate (10⁴ and 10⁵ nematodes per 30.5 row-cm) plots significantly exceeded that in high rate (10⁶ and 10⁷ nematodes per 30.5 row-cm) plots. Commercially acceptable root protection (root injury ratings below 3.0) was provided by 10⁶ nematodes per 30.5 cm of row applied to third instars, and by 10⁷ nematodes per 30.5 cm of row applied to second and third instars.

The two egg parasitoid species Trichogramma minutum Riley and T. platneri Nagarkatti are closely related. No morphological or molecular characters are known to distinguish them. Their treatment as distinct species rests on the absence of female offspring in between-species crosses. The current species definitions, which must be considered tentative, assume their natural ranges to differ, with T. minutum occurring east of the Rocky Mountains and T. platneri occurring to the west. Both species are used throughout North America for the biological control of moths in orchards and forests. They are available to growers and researchers through a large number of biological control suppliers. Because the species can only be identified after crosses with known cultures, it is likely that producers often cannot be sure of the identity of their wasps. Here we studied the causes of the lack of female offspring in the between-species crosses and what happened when one species is released for biological control in the native area of the other. Our results show that females in between-species crosses are inseminated and use the sperm to fertilize their eggs, but that these fertilized eggs die. In addition, females do not preferentially mate with males of their own species when exposed to conspecific and nonconspecific males. These results are used in a model to predict the effect of releasing the non-native species in the native area of the other species. This model shows that such introductions can result in a prolonged and substantial reduction of intended biological control.

Responses of the opiine larval parasitoid Diachasmimorpha tryoni (Cameron) to the fruit-feeding Mediterranean fruit fly, Ceratitis capitata (Wiedemann), and the gall-forming lantana gall fly, Eutreta xanthochaeta Aldrich, were evaluated in greenhouse and open-door laboratory cages. In greenhouse cages, coffee plants containing C. capitata-infested fruit and lantana twigs containing E. xanthochaeta galls were presented to gravid D. tryoni under both choice and no-choice conditions. Regardless of the type of assay, D. tryoni strongly preferred landing on infested coffee plants to landing on galled lantana twigs. The wasp also strongly preferred landing on C. capitata-infested coffee fruits to E. xanthochaeta galls. In addition, when released directly onto a host-habitat complex, parasitoids had significantly stronger probing responses to C. capitata-infested coffee fruit than to E. xanthochaeta galls. However, the stronger probing response to coffee (shorter latency and longer duration) by D. tryoni did not result in higher rates of attack on C. capitata larvae than on gall fly larvae. When measured by the number of host larvae attacked per unit time spent probing, D. tryoni was significantly more efficient in attacking lantana gall fly larvae in stem galls than C. capitata larvae in coffee berries. When lantana patches containing galls were presented to D. tryoni in open-door laboratory cages under different regimes of availability of C. capitata or its fruit hosts, rates of attack on lantana gall flies by D. tryoni were significantly reduced by the presence of coffee plants containing C. capitata-infested berries. This result suggests that host switching of D. tryoni from C. capitata to lantana gall fly in the field is likely to be affected by the spatial and temporal distributions of the two hosts and their plant habitats. Relevance of our findings to host-switching of D. tryoni and the risk of significantly impacting populations of nontarget lantana gall flies are discussed.

Laboratory feeding experiments using transgenic Bacillus thuringiensis variety kurstaki (Berliner) corn plants were carried out to study the effects of B. thuringiensis-fed herbivorous prey on the predator Orius majusculus (Reuter). Host plants were a transgenic B. thuringiensis-expressing (Cry1Ab) corn hybrid and the corresponding untransformed isogenic B. thuringiensis-free corn hybrid. The herbivorous prey species used in the experiment was Anaphothrips obscurus (Müller), a thysanopteran pest of corn, not sensitive to Cry1Ab toxin. The objectives were to quantify the effects of B. thuringiensis-fed prey on the development and mortality of immature O. majusculus. There was no significant difference in total mean mortality from hatch to adult eclosion between O. majusculus nymphs reared on B. thuringiensis-fed or B. thuringiensis-free prey. Similarly, no significant differences in total developmental time of O. majusculus was detected when reared on the two different prey types. Overall mortality was low, confirming that the methodology used was appropriate. We propose this approach as an efficient standardized preregistrational testing for side effects of transgenic plants on small predators such as Orius spp.

The effects of temperature on insect life history were studied for two whitefly hosts (Homoptera: Aleyrodidae), the silverleaf whitefly, Bemisia argentifolii Bellows & Perring, and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), as well as the parasitoid, Eretmocerus eremicus Rose & Zolnerowich (Hymenoptera: Aphelinidae) attacking both hosts. Mean egg numbers as a function of time were fitted to models for age-specific oviposition for each whitefly. For B. argentifolii, numbers of eggs laid increased with time at 15, 21, and 24°C. At 28 and 32°C, the curve declined after 6 d, although the model fit was poor. The model did not fit the oviposition data at 32°C. Maximal oviposition rate occurred at 24°C (12 eggs per 48-h period), and the model was almost linear. For T. vaporariorum, the model closely fit mean eggs laid, with highest rates of ≈12 eggs per 48 h at 21 and 24°C. Numbers of whitefly eggs as a function of time and temperature were described by a three-dimensional surface model that was also used to estimate temperature thresholds for oviposition (12.5°C for B. argentifolii and 10.9°C for T. vaporariorum). Increasing temperatures produced decreased preoviposition periods in B. argentifolii, whereas temperature extremes resulted in longer periods for T. vaporariorum. Development times from egg to adult, percentage mortality, and estimated degree-days for development were measured at 15, 21, 24, 28, and 32°C for both whiteflies, and for E. eremicus reared on both hosts. Development rate was higher for B. argentifolii than T. vaporariorum at 24 and 28°C. Development of E. eremicus was faster using B. argentifolii as hosts than T. vaporariorum at 24, 28, and 32°C. By extrapolation of development rates, lower developmental thresholds (°C) were estimated as follows: T. vaporariorum, 2.92; B. argentifolii, 10.32; E. eremicus on T. vaporariorum, 5.44; and E. eremicus on B. argentifolii, 8.7. Mean degree-day requirements for egg to adult development were calculated for T. vaporariorum, 483.4; B. argentifolii, 319.7; E. eremicus on T. vaporariorum, 417.3; and, E. eremicus on B. argentifolii, 314.4. Percentage mortality also was significantly affected by temperature in both species of whitefly. For T. vaporariorum, higher temperatures caused higher levels of mortality, with almost 98% killed at 32°C. The reverse occurred in B. argentifolii, where highest levels of mortality were found at the lowest temperatures. Mortality patterns in E. eremicus reflected those of the host: increasing with temperature on T. vaporariorum, while decreasing on B. argentifolii. The life history of E. eremicus was profoundly affected by that of its host.