Native braconid parasitism of the Tarnished plant bug (Hemiptera: Miridae) in Southern Ontario

Three agricultural regions in southern Ontario (London, Niagara and Guelph) were sampled weekly from May to September for Lygus spp. and their parasitoids in 1998, 1999 and only one region in 2000. Alfalfa was the primary crop sampled, including both “clean” and weedy alfalfa fields. Lygus lineolaris (Palisot de Beauvois) accounted for 99% of all Lygus spp. collected by sweepnet. Lygus lineolaris had two generations (mid-June and late July) on alfalfa with a partial third generation in early September which contributes to the over-wintering adults. In 1998 and 2000, an early first generation peak of Lygus nymphs was observed in mid-May on the weeds, chickweed and shepherd's purse. Overall rates of parasitism (from dissections) for native parasitoids were consistent from year to year and the means of the three regions in each growing season were below 11%. Both nymphs and adult Lygus were parasitized, with the highly mobile adults being a potential means of dispersing the parasitoids. In general weedy fields were more highly parasitized than fields of weed-free alfalfa. Six species of native braconid parasitoids were collected from L. lineolaris in southern Ontario (in decreasing order of occurrence): Peristenus pallipes (Curtis), Peristenus pseudopallipes (Loan), Leiophron lygivorus (Loan), L. solidaginis Loan, L. uniformis (Gahan), and Leiophron sp. near brevipetiolatus Loan. The large populations of Lygus and the low percent baseline parasitism in southern Ontario, particularly of second generation Lygus, support the need for introduction of a multivoltine parasitoid species in this region.     

A single-step multiplex PCR assay for the detection of European Peristenus spp., parasitoids of Lygus spp.

Lygus Hahn (Hemiptera: Miridae) are serious pests of agricultural and greenhouse crops throughout North America. In Europe, bivoltine Peristenus Förster (Hymenoptera: Braconidae) species have a significant impact on Lygus populations. Release and establishment of European P. digoneutis Loan in Lygus lineolaris (Palisot de Beauvois) populations in northeastern USA has renewed interest in the intended liberation of European parasitoids for Lygus control in Canada. Accurate identification of natural enemies is the cornerstone of biological control but conventional methods for identifying Peristenus species and estimating parasitism rates rely on tedious and time-consuming dissection and rearing methods. The present study describes species-specific PCR primers for three species of Peristenus, and the use of a multiplex PCR assay to detect P. digoneutis and P. stygicus Loan eggs and larvae from Lygus rugulipennis Poppius nymphs. Results indicate that the primers amplify uniquely sized, species-specific PCR products for the three species and are capable of detecting single eggs in parasitized nymphs within 3 days post-parasitism. Using a multiplex PCR assay, the primers maintain specificity and sensitivity, and allow detection of each of the three species in a single reaction. Although molecular diagnostics have previously been used in the identification of parasitoids and estimation of parasitism rates, this is the first time a single-step multiplex PCR protocol has been described.     

Parasitism activity of Peristenus spp. (Hymenoptera: Braconidae) on Lygus lineolaris (Hemiptera: Miridae) nymphs prior to the establishment of P. digoneutis in southwestern Quebec

Parasitism of tarnished plant bug nymphs, Lygus lineolaris (Palisot de Beauvois) was investigated on different weeds and on lettuce, celery and alfalfa-clover, in a muck soil area of southwestern Quebec. The phenology of parasitism, defined as the time during which female parasitoids are active in the field, was evaluated. Two nymphal parasitoid species were found: Peristenus pallipes (Curtis) and P. pseudopallipes (Loan). Lygus lineolaris was most abundant on stinging-nettle with levels of parasitism of 17% (P. pallipes) and 27% (P. pseudopallipes) and on alfalfa-clover with levels of parasitism of 25% (P. pallipes) and 8% (P. pseudopallipes). On lettuce, parasitism by P. pseudopallipes was below 4% while no parasitism was observed on celery. The dissection and rearing methods were used to estimate parasitism, and dissection usually yielded parasitism levels higher than rearing. Degree-days requirements of both host and parasitoids were used to calculate the period of activity of parasitoid adults. The estimates of adult activity were 47 days from late May to early July for P. pallipes, and 42 days from mid-July to late August for P. pseudopallipes.     

A protein‐based approach to mark arthropods for mark‐capture type research

A series of studies was conducted to test methods for marking a wide variety of arthropods with inexpensive proteins for mark‐capture dispersal research. The markers tested included egg albumin protein in chicken egg whites and casein protein in bovine milk. The first study qualified the effectiveness of the two marks on more than 50 arthropod species inhabiting cotton via two application procedures. The application methods included: (1) a topical plus residue protein application, and (2) a residue‐only protein application. Both protein marks, regardless of the method of application, were readily retained on the arthropod assemblage over the duration of the study. The second study determined how rapidly insects acquire chicken egg albumin protein after contact exposure to cotton tissue sprayed with an egg whites solution. Under laboratory conditions, the vast majority of adult Hippodamia convergens Guérin‐Méneville (Coleoptera: Coccinellidae) and Lygus hesperus Knight (Heteroptera: Miridae) acquired the mark after 5 min, and immature Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) acquired the marker after 40 min. The third study determined how rapidly H. convergens and L. hesperus acquire bovine casein protein after contact exposure to either alfalfa, Medicago sativa L. (Fabaceae), or lesquerella, Lesquerella fendleri (Watson) (Brassicaceae), plants sprayed with a bovine milk solution. These insects rapidly acquired the casein mark from the plant residue under field conditions. A final study determined how long H. convergens retain casein protein after 24‐h exposure to alfalfa and lesquerella plants containing a 7‐day‐old residue of bovine milk. Approximately 95% of the H. convergens maintained the casein mark for 2 days after removal from each type of plant.     

Post‐mating enhancement of fecundity in female Lygus hesperus

Although mated females of the western tarnished plant bug Lygus hesperus Knight are known to produce more eggs than virgins, the nature of the inducing stimuli and the specific changes occurring in the female require additional elucidation. Compared with virgin females isolated from males, those exposed to male precopulatory behaviours produce similar numbers of eggs, whereas inseminated females produce 50% more during the observation period. Although the quantity of seminal fluids received by a female does not influence egg number, mating twice within a 10‐day span causes a 16% increase in fecundity, on average. Females mating more than twice during the same period do not exhibit additional increases in egg number. Because virgin females contain more chorionated eggs than are laid, mating appears to enhance the rate of oviposition. However, to achieve a sustained increase in fecundity, an augmented rate of oocyte maturation would also be required. Male‐derived spermatophores lack substantive quantities of nutrients that might otherwise have enhanced female fecundity. The total amounts of carbohydrate, protein and lipid, as well as eight essential minerals transferred by the male, are insufficient for producing even a single egg, and the female has already produced a large number of chorionated oocytes before she mates. Collectively, the data suggest that seminal fluid contains one or more activational molecules, such as a peptide, which triggers an increase in egg deposition. A prolonged increase in oviposition rate may be achieved through multiple matings to ensure a supply of sperm or to offset the degradation of the putative activational factor.     

Application of hydrophilic–lipophilic balance (HLB) number to optimize a compatible non-ionic surfactant for dried aerial conidia of Beauveria bassiana

The hydrophilic–lipophilic balance (HLB) number system was used to optimize a compatible non-ionic surfactant, TDA (polyoxyethylene tridecyl ether) in formulations for two Beauveria bassiana strains, NI8 and GHA. The optimal HLB number for TDA was determined on the basis of wetting times for conidial powders. The results indicated that optimal HLB number of TDA for B. bassiana strain NI8 was 8, while the optimum HLB number for strain GHA was 10. The optimized TDA surfactants required significantly less wetting times than the commonly used laboratory surfactants, Triton X-100, Span 80, and Tween 80. These optimized TDA surfactants were further characterized on their ability to produce conidial suspensions of the two strains after 5 min of mixing, TDA HLB 8 and TDA HLB 10 produced suspensions of 1.8 × 10⁸ and 1.6 × 10⁸ conidia/ml for NI8 and GHA, respectively. These conidial levels were significantly higher than those in Triton X-100, Span 80, and Tween 80 suspensions after the same mixing time. Germination assays showed that TDA HLB 8 promoted significantly higher germination rates of strain NI8 than those observed in other commonly used laboratory surfactants. However, the germination rates of the GHA strain were unaffected by any of the surfactants tested. The efficacy of the conidial suspensions was confirmed with assays against Lygus lineolaris. Bioassay results indicated that there were no significant differences in mortalities because of surfactants. These results suggest optimization based upon HLB number will not negatively impact parameters associated with efficacy, while providing desirable physical properties.     

Development times and fecundity of three important arthropod pests of strawberry in the United Kingdom

The development rates and fecundity of three important pests of strawberry in the UK were determined over a range of temperatures. Development time of the strawberry tarsonemid mite, Phytonemus pallidus, from egg lay to adult, ranged from a mean of 28.4 days at 12.5°C to 8.8 days at 25°C. No nymphs developed to adult at 10°C. Females lived for up to 45 days and laid a mean of 24.3 and 28.5 eggs at 20°C and 25°C respectively. Total development time from egg lay to adult for the strawberry blossom weevil, Anthonomus rubi, ranged from a mean of 95.7 days at 10°C to 18.2 days at 25°C. Mean fecundity at 20°C was 157.6 eggs, and the oviposition period averaged 71.6 days. When nymphs were reared on strawberry, development of the European tarnished plant bug, Lygus rugulipennis, from egg lay to adult, ranged from 83.8 days at 15°C to 28.8 days at 25°C. Development times on groundsel were shorter and ranged from 65.6 to 22.2 days at 15°C and 25°C. Only two nymphs developed to adults at 10°C; no eggs hatched at that temperature. Mean fecundity at 20°C was 75.4 eggs, but ranged from 23 to 179. Under a fluctuating temperature regime of 10°C for 12 h:20°C for 12 h, nymphs of L. rugulipennis took 40.3 days to become adult on strawberry, and 33.4 days on groundsel. Simple linear models fitted the developmental rate ‐ constant temperature relationship well for all species, accounting for 95–98% of the total variation in observed developmental rates. Development under fluctuating temperatures illustrated the potential problem of extrapolating linear models beyond the conditions of the experiment.     

Development and validation of a model forecasting the phenology of European tarnished plant bug Lygus rugulipennis in the U.K

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