Characterization of eight polymorphic microsatellite markers in the tarnished plant bug,Lygus lineolaris (Palisot de Beauvois)

A partial genomic library of the tarnished plant bug, Lygus lineolaris, enriched for microsatellite sequences was screened to identify marker loci. Eight polymorphic loci suitable for population genetic studies were identified by screening 192 field‐collected insects. The observed number of alleles ranged from four to 21 with an average of 12.25 (SE ± 1.94) while the effective number of alleles ranged from 1.23 to 11.05 with an average of 4.49 (SE ± 1.15). No linkage disequilibria or significant deviations from Hardy–Weinberg expectations were detected at any of the loci. Seven of the eight L. lineolaris microsatellite loci were transferable to Lygus hesperus.     

Characterization of microsatellite loci in the western tarnished plant bug,Lygus hesperus Knight (Hemiptera: Miridae)

A microsatellite‐enriched partial genomic DNA library of Lygus hesperus was generated and screened by sequencing. Ten polymorphic microsatellite marker loci were characterized by genotyping 92 insect samples. The observed number of alleles ranged from three to seven with an average of 4.5 (SE ± 0.45), while the effective number of alleles ranged from 1.21 to 3.02 with an average of 2.14 (SE ± 0.20). Significant deviations from Hardy–Weinberg expectations were detected at three loci. Significant linkage disequilibrium was also detected between the loci LhMS2‐54 and LhMS3‐32. Seven of the L. hesperus markers could be transferred to Lygus lineolaris.     

State-dependent sampling bias in insects: implications for monitoring western tarnished plant bugs

Insect populations vary in the proportion of individuals exhibiting a particular ‘state’ (e.g., developmental stage, sex, egg load, or nutritional status). Because an insect's developmental state often determines both its size and its behavior, it is likely that this will also affect the probability of being sampled. We propose that a comprehensive approach to pest management must consider the interaction between the structure of a pest population (i.e., the relative number of individuals in each state) and any state‐dependent sampling bias. To illustrate the usefulness of this method we sampled populations of the western tarnished pest bug, Lygus hesperus Knight (Heteroptera: Miridae), in cotton fields. Our sampling technique utilized large cages to measure the absolute densities of each L. hesperus stage and adult sex within a population. This technique allowed us to document a wide range of absolute stage structures and sex ratios across 10 L. hesperus populations in California. Using a combination of cage samples and sweep net samples, we quantified the state‐dependent sampling bias by calculating the efficiency of sweep sampling as a function of L. hesperus developmental stage and sex. We found that the efficiency of sweep nets increased steadily with each successive developmental stage (i.e., nymphal instar) of L. hesperus. We also found that sweep nets are slightly more efficient in capturing male vs. female L. hesperus adults. Since other studies have documented that the stage and sex of L. hesperus can affect feeding impact on cotton flower buds, our results suggest that accurate predictions of Lygus damage will need to incorporate stage and sex‐dependent sampling biases.     

Escape of Lygus hesperus (Heteroptera: Miridae) Eggs from Parasitism by Anaphes iole (Hymenoptera: Mymaridae) in Strawberries: Plant Structure Effects

Herbivorous insects in natural and agricultural systems experience variation in parasitoid attack on different plant species due to direct and indirect plant influences on parasitoids. Lygus hesperus is a native polyphagous mirid that suffers up to 100% parasitism by the native egg parasitoid Anaphes iole in certain weed hosts, but with inundative releases in commercial strawberries, we achieve <65% L. hesperus suppression. We examined L. hesperus egg distribution in individual strawberry plants and parasitism by A. iole of eggs in different strawberry plant structures to determine whether plant-related factors affected parasitoid performance in strawberries. L. hesperus laid more eggs (46.5% of all eggs laid) in the fruit (between the achenes [seeds] in the fleshy receptacle) than in the petiole (23.3%), leaflet (20.3%), peduncle (6.2%), or calyx (3.7%). In a no-choice test, parasitism by A. iole was higher in the petiole (96.7%), calyx (91.9%), and leaflet (85.2%) than in the fruit (51.8%), in which the achenes appeared to hinder parasitoid access to host eggs. In addition, in young fruits in which the interachene distance was minimum, parasitism was considerably lower (25.4%) than in fruits in which receptacle swelling had resulted in interachene distances that were medium (65.7% parasitism) or large (77.1% parasitism). Our results suggest that strawberry fruits can provide refugia from parasitism by A. iole and that maximum protection occurs when the achenes are contiguous. The presence of refugia in strawberries limits the impact of augmentative biological control with A. iole, highlighting the need for its integration with other strategies to effectively suppress L. hesperus in strawberries.     

Estimating parasitism levels in Lygus spp. (Hemiptera: Miridae) field populations using standard and molecular techniques

Host dissection, host rearing and PCR analysis were used to estimate parasitism level and identify the parasitoid complex in Lygus spp. populations in alfalfa. Parasitism level estimates by PCR were higher than by other methods. The PCR results from all samples tested with available primers were consistent with Peristenus pallipes, although the parasitoid was identified as Peristenus near mellipes by morphological characters.     

Polygalacturonase causes lygus-like damage on plants: cloning and identification of western tarnished plant bug (Lygus hesperus) polygalacturonases secreted during feeding

Polygalacturonase (PG), an enzyme that degrades pectin within the plant tissue cell wall, has been postulated as the chemical cause of damage to plants by the mirid Lygus hesperus. Micro-injection of two pure recombinant Aspergillus niger PG II protein forms, the wild type enzymically active and the mutant inactive one, into alfalfa (Medicago sativa L.) florets, demonstrates that the enzymatic activity rather than the PG protein structure per se elicits damage symptoms. A PG gene family has been described for the tarnished plant bug, L. lineolaris. Here we report cloning members of the L. hesperus PG gene family, Lhpg2, obtained with L. lineolaris PG-specific primers and a novel Lhpg4, amplified with degenerate primers that were designed based, in part on the N-terminal sequence from an active, partially purified L. hesperus salivary gland PG protein. Proteomic analyses revealed that the salivary gland PGs encoded by Lhpg2 and Lhpg4 are detected in a diet into which L. hesperus has extruded its saliva when feeding. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: Henryk Czosnek     

Olfactory Responses of <Emphasis Type="Italic">Anaphes iole</Emphasis> (Hymenoptera: Mymaridae) to Volatile Signals Derived from Host Habitats

Anaphes iole Girault is a frequent parasitoid of Lygus spp. eggs in the United States, and has potential as a biological control agent against Lygus hesperus Knight in different crops. Feeding and oviposition by L. hesperus induce emission of plant volatiles, but studies to date do not address the role of plant volatiles in the host-searching behavior of A. iole. In this study, a four-arm olfactometer was used to test the responses of female parasitoids to odors emanating from cotton (Gossypium hirsutum L., Malvaceae) plants damaged by L. hesperus females, L. hesperus males, larvae of the nonhost Spodoptera exigua Hubner, or mechanically, or to odors from L. hesperus females alone. In addition, various plants damaged by L. hesperus females were evaluated in the olfactometer: cotton, alfalfa (Medicago sativa L., Fabaceae), common groundsel (Senecio vulgaris L., Asteraceae), annual ragweed (Ambrosia artemisifolia L., Asteraceae), and redroot pigweed (Amaranthus retroflexus L., Amaranthaceae). In all olfactometry bioassays, treatment odors were compared against three controls (humidified air). Results showed that A. iole females were consistently attracted to odors derived from different plant–L. hesperus complexes, while odors from plants subjected to nonhost (S. exigua) or mechanical damage and L. hesperus females alone were not attractive or only variably attractive. These findings suggest that while searching for hosts A. iole females use specific volatiles induced by L. hesperus feeding and oviposition to locate hosts inhabiting a wide variety of plants, including annual and perennial species from four plant families. It was suggested that future research should seek to identify the chemical elicitors involved in the release of plant volatiles attractive to A. iole females.     

Integrating pesticide effects with inundative biological control: interpretation of pesticide toxicity curves for Anaphes iole in strawberries

We examined pesticide residue effects on the egg parasitoid Anaphes iole Girault (Hymenoptera: Mymaridae), an inundative biological control agent for Lygus hesperus Knight (Heteroptera: Miridae) in strawberries (Fragaria × ananassa Duchesne). Our objectives were to identify compatible pesticides, determine appropriate parasitoid release timings for minimizing harmful effects, and develop an approach for interpreting pesticide toxicity curves. Six insecticides, 2 acaricides and 6 fungicides were tested, and survivorship of adult A. iole exposed to foliar residues for 48 h, at 4–6 different times after pesticide application, was examined. A logistic function was developed for incorporating control mortality at each test date. Values for LT₅₀ (Lethal Time for 50% mortality) and mortalities on day 1 (initial mortality) and day 13 (estimated maximum time parasitoid releases can be delayed under extreme summer conditions) were estimated. In the study, insecticide residues proved to be the most toxic, followed by those from acaricides while most fungicides were least toxic. Among insecticides, fenpropathrin, bifenthrin and carbaryl caused the greatest mortality (estimated mortality on day 13 >75%). Residues of naled resulted in the least mortality (LT₅₀=3.2 days) followed by methomyl (LT₅₀=8.3 days) and malathion (LT₅₀=13.2 days). Estimated mortality = 12.3% on day 13 for the acaricide propargite and <1% for abamectin. For the fungicides benomyl, captan, myclobutanil and thiram, estimated mortality on day 1 was <1%, and for iprodione it was <6%, indicating compatibility with A. iole releases. For sulfur, LT₅₀=0, but the mortality decay curve was relatively flat (estimated mortality on day 13=13.6%). These results suggest possibilities for integrating A. iole releases with certain pesticide programs by appropriate timing of pesticide applications to minimize negative impacts.     

Bioclimatic analyses of distributions of a parasitoid Peristenus digoneutis and its host species Lygus spp. in Europe and North America

• 1 Peristenus digoneutis Loan is a parasitoid of Lygus plant bugs, which was successfully introduced from Europe into North America in the 1980s for controlling native Lygus populations. Surveys confirmed that P. digoneutis populations have become established throughout eastern North America and that the spread of the parasitoid continues. For unknown reasons, previous releases of P. digoneutis in Western Canada were not successful.
• 2 A bioclimate (climex ®; Hearne Scientific Software Pty Ltd, Australia) model for P. digoneutis in North America was developed, based on climate and ecological parameters, and then validated with actual distribution records. The current distribution of P. digoneutis in eastern North America was consistent with the predicted distribution. The model suggests that P. digoneutis will probably continue its spread westwards throughout the U.S.A. along the Great Lakes.
• 3 The southern distribution of P. digoneutis is expected to be limited by hot summer temperatures, whereas its northern range is limited by the number of Lygus host generations rather than cold stress.
• 4 Peristenus digoneutis has the potential to occur in the southern parts of the prairie ecozone of western Canada; however, Ecoclimatic Index values in the prairies indicate mainly marginal or unfavourable conditions, which may explain why earlier releases of P. digoneutis in Western Canada failed.