Plathypena Scabra Research Articles

AFLP analysis of the entomopathogen Nomuraea rileyi

The dimorphic, asexual entomopathogen Nomuraea rileyi is a well known mortality agent of noctuid insects in subtropical and temperate agricultural systems. Genomic DNA was extracted from N. rileyi isolates collected from Anticarsia gemmatalis velvetbean caterpillar in Florida, Brazil, and Argentina as well as from non-Anticarsia hosts and subjected to a modified single-step AFLP analysis. Compared to RAPDs, the employed AFLP method provided a reliable and sensitive method for detecting genomic differences among N. rileyi populations. All ten AFLP primers produced polymorphic bands when used to amplify the different Nomuraea DNA samples. Approximately 65% (141 bands) of the total scorable bands (216) detected with ethidium bromide were polymorphic and ranged 400–3000 bp. A total of 43 haplotypes were found among the 73 N. rileyi isolates. Analysis of the AFLP data revealed extensive polymorphism among different N. rileyi isolates derived from both homologous and heterologous noctuid host species. For example, the dominant haplotype isolated from the Florida A. gemmatalis population was detected in diseased Pseudoplusia includens soybean looper and Plathypena scabra green cloverworm. Cluster analysis demonstrated that the AFLP polymorphisms observed among the N. rileyi isolates were associated with geographical location and/or with local insect population (s). Examination of this entomopathogen from a single field over a multiseasonal time frame demonstrated that the N. rileyi population is stable and can probably overwinter and initiate the disease cycle the following year.

AFLP Analysis of the Entomopathogen Nomuraea rileyi

The dimorphic, asexual entomopathogen Nomuraea rileyi is a well known mortality agent of noctuid insects in subtropical and temperate agricultural systems. Genomic DNA was extracted from N. rileyi isolates collected from Anticarsia gemmatalis velvetbean caterpillar in Florida, Brazil, and Argentina as well as from non-Anticarsia hosts and subjected to a modified single-step AFLP analysis. Compared to RAPDs, the employed AFLP method provided a reliable and sensitive method for detecting genomic differences among N. rileyi populations. All ten AFLP primers produced polymorphic bands when used to amplify the different Nomuraea DNA samples. Approximately 65% (141 bands) of the total scorable bands (216) detected with ethidium bromide were polymorphic and ranged 400-3000 bp. A total of 43 haplotypes were found among the 73 N. rileyi isolates. Analysis of the AFLP data revealed extensive polymorphism among different N. rileyi isolates derived from both homologous and heterologous noctuid host species. For example, the dominant haplotype isolated from the Florida A. gemmatalis population was detected in diseased Pseudoplusia includens soybean looper and Plathypena scabra green cloverworm. Cluster analysis demonstrated that the AFLP polymorphisms observed among the N. rileyi isolates were associated with geographical location and/or with local insect population (s). Examination of this entomopathogen from a single field over a multiseasonal time frame demonstrated that the N. rileyi population is stable and can probably overwinter and initiate the disease cycle the following year.

Influence of Irrigation and Maturity Group on the Seasonal Abundance of Soybean Arthropods

The effects of irrigation and soybean maturity group (Group V ‘Forrest’ variety vs Group VII ‘Braxton’ variety) on the seasonal abundance of arthropod pest and beneficial population densities were examined in large-plot field tests at the Attapulgus Research Center in Attapulgus, GA, in 1987 through 1990. In general, soybean plant growth was more abundant, yields were higher, and canopy closure indices were lower in irrigated than in non-irrigated plots for both varieties. Irrigation and the resultant increased soybean vegetation supported a greater overall seasonal abundance of all five of the insect pests monitored: stink bugs, primarily Nezara viridula (L.), velvetbean caterpillars, Anticarsia gemmatalis Hübner, soybean loopers, Pseudoplusia includens (Walker), threecornered alfalfa hoppers, Spississtilus festinus (Say), and green cloverworms, Plathypena scabra (F.). No overall varietal effects were noted for N. viridula; however, each year, population densities were higher in the early-maturing ‘Forrest’ up to julian day 250 then densities were higher in the later-maturing ‘Braxton’ for the remainder of the grown season. Mean estimates of the seasonal abundance of A. gemmatalis and P. scabra populations were similar between the two varieties; however, P. includens and S. festinus were more abundant on Forrest than on Braxton. Total arthropod predators, including Nabis spp., Geocoris spp., and spiders, also were more abundant on irrigated soybeans, while overall varietal means were similar. Yearly analyses revealed significant irrigation and variety effects for most of the species sampled.

Response of Soybean Insect Communities to Row Width Under Crop-Residue Management Systems

The impact of narrow-spacing and crop-residue management systems on soybean insect communities was investigated from 1993 to 1995. Field studies were conducted to determine the effect that row width has on the population dynamics of phytophagous insects and their natural enemies in soybeans [ Glycine max (L.) Merrill] grown under 2 crop-residue management systems. Soybeans were planted in a split-plot design with no-till and reduced-till residue management, and with narrow and wide row spacings. The above-ground insect populations were estimated by sampling at 2-wk intervals. In addition, several environmental factors, including air and soil temperatures, relative humidity, leaf area index, and estimated weed escapes percentage were recorded and used to explain the insect population dynamics. The predominant insect pests found were potato leafhoppers [ Empoasca fabae (Harris)], green cloverworms [ Hypena scabra (F.)], bean leaf beetles [ Cerotoma trifurcata (Forster)], brown stink bugs ( Euschistus spp.), differential and red-legged grasshoppers [ Melanoplus differentialis (Thomas) and Melanoplus femurrubrum (De Geer), respectively], and tarnished plant bugs [ Lygus lineolaris (Palisot de Beauvois)]. Common natural enemies found were damsel bugs ( Nabis spp.) and insidious flower bugs [ Orius insidiosus (Say)]. No significant differences were detected between populations of insect pests from narrow versus wide row-spacing treatments; however, population densities of potato leafhoppers and bean leaf beetles were significantly greater in the reduced-till plots compared with the no-till plots. Likewise, no significant differences were observed among natural enemies for the tested combinations of row spacing and tillage practice. The results of this study support the hypothesis that different row widths do not dramatically affect insect communities in soybean grown under no-till and reduced-till crop-residue management systems.

Selected Insecticides for Control of Corn Earworm and Green Cloverworm in Soybean in Virginia, 1997

Abstract Efficacy of selected insecticides was evaluated against CEW and GCW in soybean. ‘Hutcheson’ soybean was planted 15 June in a producer’s field in Greensville County, VA, using an 18-inch row spacing. All treatments were broadcast as foliar sprays with water on 27 August using a CO2 pressurized backpack sprayer calibrated to deliver 14.3 gpa at 18 psi through 8002VS flat fan nozzles spaced 18 inches apart on the spray boom. A RCB experimental design was used with 4 replicates; plots were 4 rows by 50 ft. Insect samples were taken using a 15-cm diameter sweep net, 15 sweeps per plot. Pre-treatment insect populations were assessed just prior to treatment application by taking several 15-sweep samples throughout the planned test area. Post-treatment samples were taken 2, 4, 8, 12, and 21 days after treatment (DAT) by comparing numbers of small (1st and 2nd instars), medium (3rd and 4th instars), large (5th and 6th instars) and total CEW larvae, and total (all sizes) GCW larvae. Data were analyzing using ANOVA and LSD statistical procedures.

Comparison of Orius insidiosus (Heteroptera: Anthocoridae) and Nabis roseipennis (Heteroptera: Nabidae) as Predators of the Green Cloverworm (Lepidoptera: Noctuidae)

The ability of nymphal and adult Orius insidiosus (Say) to prey upon eggs and early instars of the green cloverworm, Plathypena scabra (F.), was determined in the laboratory. Second instars, 4th instars, adult males, and females of the predator were tested separately on excised soybean leaflets in small arenas. All tested instars and stages of O. insidiosus fed upon eggs and 1st instars of the green cloverworm, with older predators consuming more prey than younger predators. Fourth instars and adults also preyed upon 2nd-instar caterpillars. No stage of O. insidiosus was able to feed upon 3rd instars of the green cloverworm. Using potted soybean plants, we compared the mortality inflicted on eggs and 1st and 2nd instars of the green cloverworm by O. insidiosus and Nabis roseipennis Reuter when the 2 predator species searched alone and in combination. Regardless of prey stage or instar, N. roseipennis consumed far more prey than did O. insidiosus when the predators were tested separately. When the 2 predator species searched for prey together, mortality inflicted by adult O. insidiosus and adult N. roseipennis appeared to be additive; in other combinations of predator stages or instars, combined predation by the 2 predator species did not differ from that observed for N. roseipennis alone. Despite low individual predation rates, O. insidiosus should not be discounted as a potentially important predator of green cloverworm eggs and small larvae in soybean fields, because it is often the most abundant predaceous species associated with this crop.

Allocation of searching time within the soybean canopy by parasitoids attacking the green cloverworm

We examined the searching behavior of a guild of primary parasitoids which attack the green cloverworm,Plathypena scabra (Fabricius), as well as that of an associated hyperparasitoid. We hypothesized that self-superparasitism is an important constraint on the foraging behavior of primary parasitoids, and therefore these parasitoids should avoid portions of the soybean canopy where parasitized caterpillars accumulate. Conversely, we hypothesized that the hyperparasitoid preferentially searches parts of the canopy where parasitized caterpillars accumulate. In a greenhouse experiment, we found that exposure to parasitoids [eitherCotesia marginiventris (Cresson) orDiolcogaster facetosa Ashmead] resulted in the accumulation of caterpillars lower in the canopy. In a field experiment, we measured the amount of time parasitoids spent searching in each of three strata (upper, middle, bottom) of the soybean canopy. Leaf area in each stratum was used to calculate expected values for search effort. The time spent searching each of the strata was proportional to leaf area for all primary parasitoids, exceptD. facetosa, which spent significantly more time searching the top stratum of plants than predicted by leaf area in that stratum. The hyperparasitoidMesochorus discitergus (Say) tended to search the bottom stratum of the canopy. Thus only one of the three primary parasitoids appears to search in a manner that would reduce its rate of encounter with previously parasitized green cloverworms. The hyperparasitoid searching pattern may increase its probability of encountering parasitized caterpillars, thereby increasing its foraging success.

Parasitism and Disease Incidence in the Green Cloverworm (Lepidoptera: Noctuidae) in Strip-Intercropped Soybean Agroecosystems

We examined the effects of strip-intercropping soybean, Glycine max , and sorghum, Sorghum bicolor , on rates of insect parasitism and fungal disease incidence in larvae of the green cloverworm, Plathypena scabra (F.), a widespread and occasionally serious pest of soybeans, during an endemic year. A completely randomized design with two cropping systems (monocropped soybean and soybean intercropped with sorghum), two sorghum heights (dwarf sorghum ≈1 m in height; tall sorghum ≈2 m in height), and two row patterns (2 rows of sorghum alternating with 10 rows of soybean; 6 rows of sorghum alternating with 6 rows of soybean) was used. Abundance (number per row-meter) of P. scabra larvae, rates of larval parasitism and incidence of the entomopathogenic fungus, Nomuraea rileyi (Farlow) Sampson did not differ significantly among treatments or their interaction. Soybean yield (grams dry weight of beans per row-meter) did not differ significantly among treatments but sorghum grain yield and biomass (grams dry weight per row-meter) were significantly lower in dwarf sorghum planted in wide rows because of competing weed populations. Results suggest that neither the accrual of P. scabra larvae in soybean nor the impact of the parasitoid-pathogen complex on P. scabra mortality is affected by structural or taxonomic agroecosystem diversification at the scale studied. n

The Effect of Alternative Southern Green Stink Bug (Heteroptera: Pentatomidae) Insecticide Controls on Soybean Pest Management, Quality and Yield

Seven alternative insecticides to methyl parathion were assessed for stink bug control and yield and quality losses in soybean field trials in Georgia, Louisiana and Florida during 1988 and 1989. Several pyrethroid insecticides including lambda-cyhalothrin, cyfluthrin, tralomethrin and cypermethrin controlled the southern green soybean stink bug, Nezara viridula (L.). These insecticides had greater residual control than methyl parathion, the standard for stink bug control, and acephate, another labeled soybean insecticide. The residual control of the pyrethroids also prevented the buildup of green cloverworm, Plathypena scabra (F.), velvetbean caterpillar, Anticarsia gemmatalis Hübner, and bean leaf beetle, Cerotoma trifurcata (Forster). Permethrin, another pyrethroid insecticide, did not provide adequate stink bug control at the rate tested. Yields and 100-seed weights in the alternative insecticide plots were equal to or exceeded those in the standard treatments. Soybean quality (lower percentage of stink bug damaged kernels) was higher in plots treated with pyrethroids. Several alternative insecticides for controlling stink bugs are available to replace methyl parathion in soybean, should this product become unavailable to producers due to its patent expiration or denial of re-registration.

Orientation of a hemipteran predator to vibrations produced by feeding caterpillars

Observations of search behavior in the predatory stinkbugPodisus maculiventris (Say) suggested that vibrations produced by prey as they chew on leaves may be an important cue used by this predator to locate prey. To test this hypothesis, studies were conducted to determine ifP. maculiventris search and make directional choices in response to vibrational stimuli produced by feeding green cloverworms,Plathypena scabra (F.), and to recordings of chewing vibrations. Modified soybean plants [Glycine max (L.)] were used in Y-choice tests. Individuals exposed to vibrational signals finished trials significantly more often on branches through which vibrations entered the plants than on no-stimulus branches. Also, a significantly higher proportion of individuals that initially moved onto branches with no stimulus reversed course than did those moving up branches with vibrational stimuli. The response ofP. maculiventris individuals to vibrational signals produced by a common prey species demonstrates that these predators are capable of using substrate-borne vibrations as cues for prey location.

Growth of Soybean Stressed by Nematodes, Herbicides, and Simulated Insect Defoliation

AbstractSoybean [Glycine max (L.) Merr.] responses to combinations of stress factors generally are unknown. Research was conducted in 1989, 1990, and 1991 to quantify growth responses to stresses from soybean cyst nematode (SCN; Heterodera glycines Ichinohe), acifluorfen {5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoic acid} plus bentazon [3‐(1‐methylethyl)‐(1H)‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide] herbicides, and simulated green cloverworm [GCW; Plathypena scabra (F.)] defoliation. Treatments were combinations of at‐planting SCN soil density, acifluorfen plus bentazon rate, and simulated GCW defoliation level. Herbicides were applied at V6 soybean development, and GCW feeding was simulated from R2 to R4 soybean development. Plant growth was quantified at V4, R2, and R4 developmental stages. Herbicide stress was assessed by leaf stomatal conductance and visible foliar injury. Herbicides reduced conductance and caused visible injury each year, and limited growth (plant height, leaf area, pod number, and dry weight of leaf, pod, and stem plus petiole) in 1990 and 1991. Likewise, defoliation reduced leaf area each year, but reduced growth (plant height and leaf dry weight) in 1990 and 1991 only. Uncontrolled environmental factors probably confounded growth responses in 1989. Although no herbicide × defoliation effects on growth were found, defoliation caused greater reductions in canopy quantity and quality for herbicide‐injured plants in 1990 and 1991. Targeted stress from SCN was achieved in 1990, and interaction with herbicides decreased conductance, increased visible herbicide injury, and reduced leaf area, plant height, pod number, and pod dry weight. These data support the potential for stresses from SCN and acifluorfen plus bentazon to cause more‐than‐additive reductions in soybean growth.

Developmental Stages and Kairomones from the Primary Parasitoid Cotesia marginiventris (Hymenoptera: Braeonidae) Affeet the Response of the Hyperparasitoid Mesochorus discitergus (Hymenoptera: Ichneumonidae) to Parasitized Caterpillars

The hyperparasitoid Mesochorus discitergus (Say) discriminates among unparasitized Plathypena scabra (F.), Helicoverpa zea (Boddie), Pseudoplusia includens (Walker), and Spodoptera frugiperda (J. E. Smith) caterpillars and those parasitized by the primary parasitoid Cotesia marginiventris (Cresson). M. discitergus females detect C. marginiventris within 1 h after parasitism of either P. scabra (green cloverworm) or S. frugiperda (fall armyworm). The time spent handling parasitized green cloverworms and fall army worms increases until after hatch of the C. marginiventris egg. C. marginiventris eggs did not appear to be suitable hosts for the hyperparasitoid, whereas first instars were. Therefore, the difference in handling times between caterpillars with egg or larval C. marginiventris may be related to the time a M. discitergus female needs to locate and parasitize a C. marginiventris larva. Results of injecting crude extracts from the C. marginiventris calyx region, or venom gland and venom reservoir, into fall armyworm larvae suggest that the venom gland extract causes changes in the hemocoel of fall armyworms that are used by M. discitergus as kairomones to discriminate between parasitized and unparasitized caterpillars. Our results do not exclude the possibility that calyx fluid too has kairomonal properties.

Behavioral Interactions Between the Hyperparasitoid Mesochorus discitergus (Hymenoptera: Ichneumonidae) and Four Species of Noctuid Caterpillars: Evasive Tactics and Capture Efficiency

The hyperparasitoid, Mesochorus discitergus (Say), oviposits into larvae of primary parasitoids while the latter are developing inside various lepidopteran hosts. To accomplish hyperparasitism, M. discitergus must capture the lepidopteran larvae. We studied the evasive behaviors of 2nd-, 3rd-, and 4th instar Helicoverpa zea (Boddie) (corn earworm), Pseudoplusia includens (Walker) (soybean looper), Spodoptera frugiperda (J. E. Smith) (fall armyworm), and 2nd- and 4th-instar Plathypena scabra (Fabricius) (green cloverworm), as well as the effectiveness of these tactics in eluding capture by M. discitergus females. Most individuals of all instars of corn earworm and fall armyworm made minimal efforts to escape. Although not commonly used by corn earworm and fall armyworm, their occasional vigorous responses were effective in deterring M. discitergus females. Dropping from a leaf, either unattached or attached by a thread, was also effective for preventing capture of those two noctuid species. Soybean loopers and green cloverworms responded much more actively. Second-instars of both species dropped off the leaf on a thread, while 3rd- and 4th-instar soybean loopers commonly used vigorous responses. Fourth-instar green cloverworms used vigorous responses and dropping off the leaf. Overall, 68% of the caterpillars using the vigorous response were captured, while 39% of those dropping on a thread and about 26% of those dropping off a leaf, unattached by a thread, were captured. Green cloverworms and soybean loopers were more difficult to capture than corn earworms and fall armyworms.

Soybean Yield and Pest Management as Influenced by Nematodes, Herbicides, and Defoliating Insects

AbstractPest management strategies based on crop losses from single stress factors may be inadequate where multiple stresses occur. Consequently, experiments were conducted in 1989, 1990, and 1991 to quantify interactive effects of stresses from soybean cyst nematode (Heterodera glycines Ichinohe), acifluorfen (5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoic acid) plus bentazon [3‐(1‐methylethyl)‐(1H)‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide] herbicides, and green cloverworm [Plathypena scabra (F.)] on seed yield of soybean [Glycine max (L.) Merr.]. Treatments were combinations of at‐planting soybean cyst nematode soil density, acifluorfen plus bentazon rate, and green cloverworm defoliation level. Herbicides were applied at V6 soybean development, while green cloverworm feeding was simulated during R2 to R4 soybean development. Plot yield and yield components (pods per plant, seeds per pod, and weight per seed) were determined. Herbicide injury and defoliation independently reduced yield in 1990 and 1991. Yield reductions from defoliation were attributed to fewer pods per plant, while herbicide injury decreased pods per plant (1990) and weight per seed (1990 and 1991). Moreover, herbicide injury and defoliation interacted over 1990 and 1991 to decrease yield. Although stress from soybean cyst nematode alone never affected yield, interactions with herbicides and with defoliation reduced yield in 1990. No treatment effects on yield were found in 1989, probably due to uncontrolled environmental factors. Because of the 2‐yr herbicides × defoliation effect, lower economic injury levels for green cloverworm were developed for soybean treated with acifluorfen plus bentazon. To account for potential interactions involving soybean cyst nematode, growers will be advised to consider adjusting weed and insect management strategies for soybean fields infested with soybean cyst nematode.

Response of soybean herbivores to two agronomic practices increasing agroecosystem diversity

The effects of agroecosystem diversification on the most abundant herbivore species of soybean ( Glycine max Merrill) in Ohio were monitored during 1988, 1989 and 1990. Maize and soybean plots were arranged in a randomized complete block design with four replicates for a 3 × 2 factorial experiment. Factors were cropping systems (maize monoculture, soybean monoculture and strip intercropping of maize and soybean) and tillage systems (no-tillage and conventional tillage). The herbivore fauna of soybean was sampled by sweep net and suction net (D-Vac). Statistically significant results from at least 1 year indicated that no-tillage was favorable to Japanese beetle ( Popillia japonica Newman), grape colaspis ( Colaspis brunnea (F.)), tarnished plant bug ( Lygus lineolaris (Palisot de Beauvois)), homopterans (Cicadellidae and Cercopidae), grasshoppers ( Melanoplus spp.) and slugs (Gastropoda). Potato leafhopper ( Empoasca fabae (Harris), green cloverworm ( Plathypena scabra (F.)), and striped flea beetles ( Phyllotreta spp.) were more abundant in conventional tillage plots. Strip intercropping was favorable to green cloverworm, Japanese beetle, and grape colaspis, whereas the potato leafhopper were more abundant in monoculture plots. There was no evidence of reduced herbivory in diversified agroecosystems, as predicted by the resource concentration hypothesis.

Influence of Successional and Grassy Corridors on Parasitism of Plathypena scabra (F.) (Lepidoptera: Noctuidae) Larvae in Soybean Agroecosystems

Influences of uncultivated corridors on rates of parasitism of the green cloverworm, Plathypena scabra (F.), in soybean agroecosystems were examined. Soybeans were planted in large experimental plots (0.45 ha); three plots contained corridors of successional old-field vegetation, three plots contained corridors planted in grasses, and three plots were left undivided. Treatments were arranged in a completely random design. No significant differences in larval parasitism were observed between treatments, and location (larvae collected near corridors, ≤5 m, compared with larvae collected farther from corridors, 6–11 m) did not have a significant effect on parasitism of P. scabra larvae . Parasitism of P. scabra larvae by the total parasitoid complex, by Aleiodes nolophanae (Ashmead), and by Campylochaeta plathypenae (Sabrosky) generally increased in all treatments as the season progressed, but parasitism by C. plathypenae declined later in the season. Larval parasitism by Cotesia marginiventris (Cresson) declined over time. Larval parasitism may have been related to spatial scale.

Validation of a model for estimating leaf-feeding by insects in soybean

A computer model (AUSIMM) estimate of the total leaf area consumed by soybean, Glycine max (L.) Merrill, leaf-feeding insect larvae was compared with measured leaf area loss after feeding by endemic field infestations in 11 field experiments. Estimates of percentage defoliation and total leaf area, both at the onset of feeding by endemic insect infestations and after the insect feeding period, were also compared with yield. Insect infestations consisted of mixed sizes of green cloverworm, Plathypena scabra (F.) (Lepidoptera: Noctuidae), velvetbean caterpillar, Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae), or soybean looper, Pseudoplusia includens (Walker) (Lepidoptera: Noctuidae). Insect infestations occurred over about a 14-day period during the R5 and R6 growth stages (beginning of seed formation to pod fill). Leaf consumption varied from ∼ 1000 to 14 000 cm 2 per row-m depending on the species, number and size of larvae. The model accurately predicted leaf area consumption over all experiments. Predicted consumption increased linearly with measured leaf area loss ( p = 0.027, r 2 = 0.47). Estimated percentage defoliation at the onset of feeding by endemic infestations was ∼ 8%, and was 5% and 20–68% after the insect feeding period in treated and untreated plots, respectively. Yield decreased with an increase in estimated percentage defoliation, but the relationship was not significant. Total leaf area varied from ∼9000 to 27 000 cm 2 per row-m among experiments. Yield increased linearly with total leaf area, both at the onset of insect feeding ( p = 0.004, r2 = 0.41) and after the insect feeding period. Total leaf area remaining after insect feeding was the best indicator of soybean yield ( p = 0.002, r 2=0.46). A 30% increase in total leaf area after feeding resulted in a 168.2 kg ha −11 (2.5 bushels acre −1) increase in yield.

Reproductive Strategies of Primary Parasitoids of the Green Cloverworm (Lepidoptera: Noctuidae)

Cotesia marginiventris (Cresson), Diolcogaster facetosa (Weed), and Rogas nolophanae Ashmead, which respectively parasitize progressively older green cloverworm, Plathypena scabra (F.) larvae, produced (x ± SE) 362.7 ± 24.1, 83.2 ± 11.4, 66.3 ± 6.1 offspring, respectively, during their lifetimes. Adult female longevity at 24°C averaged lS.l ± O.S, ~3.0 ± 0.9, and 29.9 ± 2.7 d for these species, respectively. Numbers of mature eggs from dissections of 2-d-old females were 105 ± 7.1,57 ± 5.9, and 5.2 ± 0.9. Primary braconid and tachinid parasitoids of the green cloverworm exhibited decreasing observed or estimated fecundities with respect to increasing age of host larvae attacked. Decreasing fecundities of these parasitoid species may reflect increasing potential for survival until time of parasitoid emergence of the progressively older host larvae which these species attack. Other factors suggested as influencing fecundity are breadth of host range and complexity of host location, capture, and oviposition behaviors.

Effect of Insect Damage on the Growth, Yield, and Quality of Sericea Lespedeza Forage

Variations in the seasonal abundance of phytophagous foliage-inhabiting insects were examined in sericea lespedeza ( Lespedeza cuneata (Dumont) G. Don) during the second growth cycle in 1986 and 1987 and during the first and second growth cycles in 1988. Predominant insect defoliators were grasshoppers and lepidopterous caterpillars, primarily Plathypena scabra (F.) and Helicoverpa zea (Boddie). Predominant sap-feeding taxa were the membracid Spissistilus festinus (Say); plant bugs, primarily Lygus lineolam (Palisot de Beauvois); aphids, primarily Acyrthosiphon pisum (Harris); and a number of species of cicadellid leafhoppers and pentatomid stink bugs. Grasshoppers, aphids, and plant bugs were most abundant during the first cutting, whereas S. festinus , leafhoppers, and all Lepidoptera were most abundant during the second cutting. Grasshoppers, P. scabra , and total Lepidoptera typically were more abundant in low-tannin than in high-tannin cultivars, but population densities of sap-feeding insects were not associated with the tannin concentrations in sericea lespedeza cultivars. Comparison of insecticide-treated and untreated plots revealed that P. scabra caused extensive defoliation in August and September before the second cutting. No other taxa of herbivorous insects caused significant damage to sericea lespedeza. Defoliation by P. scabra reduced stem height, leaf number per stem, and leaf and stem dry weight but had little effect on forage crude protein and acid detergent fiber content. Yield loss was significant when peak densities of P. scabra were ≥2 larvae per sweep. Peak densities of about four larvae per sweep in 1986 reduced leaf dry weight by 75% and total forage yield by about 40%. However, substantial yield losses were avoided by harvesting early.

Diapause in the Parasite Diolcogaster facetosa (Hymenoptera: Braconidae)

The critical photoperiod for diapause induction was determined in the laboratory and validated in the field for Diolcogaster facetosa (Weed), a parasite of the green cloverworm. In the laboratory at constant 24°C, as well as in the field under natural conditions, the critical photoperiod for diapause induction is between 13:11 and 14:10 (L:D). Second instars are sensitive to diapause-inducing photoperiods, and diapause occurs in the final instar after it has emerged from the host and spun a cocoon. Study of diapausing individuals from the field during autumn and winter indicated that photoperiod has only a minor role, if any, in diapause maintenance or termination. The date of diapause termination was not determined, but the combination of diapause development and postdiapause development had not been completed in the field by the spring equinox.