Filter Paper Bioassay Research Articles

Physical and chemical plant characters inhibiting the searching behaviour of Trichogramma chilonis

AbstractSeveral plant characters are known to affect the searching behaviour and parasitization efficiency of Trichogramma spp. (Hymenoptera: Trichogrammatidae). In this study, plant characters contributing to the low Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) egg parasitism levels on pigeonpea (Cajanus cajan (L.) Millspaugh) were investigated. The efficiency of T. chilonis on pigeonpea was dependent on the plant structure on which the host eggs were found. In a cage experiment, more than 55% of eggs placed on leaves were parasitized, while 1% of eggs on calyxes and no eggs on pods were parasitized. In a filter paper bioassay, parasitoids were deterred by acetone and hexane surface extracts from pigeonpea pods but showed no response to water extract. The searching behaviour of the parasitoids was not affected by different solvent extracts from the surface of pigeonpea leaves. In a four‐armed airflow olfactometer, T. chilonis was repelled by volatiles from pigeonpea pods but showed no response to volatiles derived from hexane extract of pod surfaces. Volatile infochemicals and hexane surface extracts from pods of two wild Cajanus species, C. scarabaeoides (L.) Thours and C. platycarpus (Bentham) van der Maesen, were similarly deterrent to T. chilonis. The movement of the parasitoids on pigeonpea pods and calyxes was inhibited by long trichomes and wasps were trapped by sticky trichome exudates. Parasitoids walked significantly faster on leaves than on pods. The walking speed on both pods and leaves increased significantly after washing with hexane. The results presented in this paper show that the plant growth stage and the plant structures preferred by H. armigera for oviposition are the least suitable for T. chilonis, contributing to the low parasitoid efficiency on pigeonpea.

Isolates of Soil Actinomycetes with Potential for Phytotoxin Production

Agar plate screening of 220 isolates of soil actinomycetes for phytotoxin production resulted in selection of six isolates that inhibited (≥70%) one or both indicator plants for further studies. Cell-free broth of the two isolates, diluted in a 1:1 ratio, significantly reduced seed germination and radicle growth of six plants species on filter paper bioassay. Both isolates were inhibitory to velvetleaf (Abutilon theophrasti), a difficult weed to control. Phytotoxin from cell-free fermentation broth of one of the isolates (no. 48), sequestered by solvent extraction, was bioassayed on filter paper. Seed germination and growth of cress (Lepidium sativum) and barnyard-grass (Echinochloa crusgalli) were severely reduced at 1.5 and 3.0 mg/ml concentration, respectively. Solvent extract of mycelia was marginally inhibitory indicating that the phytotoxin was largely extracellular.

The influence of neuroactive pesticides on the behaviour of entomopathogenic nematodes

AbstractThe behaviour and infectivity of the infective juveniles (IJs) of two species of entomopathogenic nematodes, Steinernema carpocapsae Weiser and Steinernema feltiae Filipjev (Rhabditida: Steinernematidae), were determined after exposure to two neuroactive pesticides, oxamyl and fenamiphos, widely used against plant parasitic nematodes. Oxamyl (50 μg ml−1) initially stimulated non-sinusoidal movement in S. feltiae but had no appreciable effect on IJs of S. carpocapsae, while fenamiphos (10 and 50 μg ml−1) increased and sustained non-sinusoidal movement in both species over an observation period of 48 h. The two pesticides reduced the infectivity of both nematode species against late instar larvae of the wax moth, Galleria mellonella L. in a sand-tube bioassay when compared with controls. Infective juveniles of S. feltiae showed limited body waving behaviour on the sand surface whereas S. carpocapsae showed the full range of nictation movements, including body waving, stationary straight postures and leaping. Oxamyl had no significant (P>0.05) effect on the number of IJs of S. carpocapsae which nictated except when the IJs were pre-incubated with this compound for 24 h (P<0.05). In contrast, fenamiphos completely suppressed all nictation and body waving behaviour in both species. Nictating IJs of S. carpocapsae exposed to late instar G. mellonella for 12 h in a filter-paper bioassay were found to be more infective compared with non-nictating IJs. Treating IJs of S. carpocapsae with oxamyl (50 μg ml−1) increased the infectivity of non-nictating IJs compared with controls but reduced infectivity of nictating IJs when exposed to G. mellonella for 12 h. The work is discussed in relation to proposals to use these or other pesticides to enhance the activity and infectivity of IJs of entomopathogenic nematodes.

Malathion Resistance in Field Strains of the Warehouse Pirate Bug (Heteroptera: Anthocoridae) and a Prey Species Tribolium castaneum (Coleoptera: Tenebrionidae)

A filter paper bioassay was used to determine sensitivity of laboratory strains of the warehouse pirate bug, Hylocoris flavipes (Reuter), and one of its prey, larvae of the red flour beetle, Tribolium castaneum (Herbst), to malathion. LD 50 for adult X. flavipes were estimated to be 51.4 μm (AI) per filter for males and 45.9 μm (AI) per filter for females. Larvae from a laboratory strain of T. castaneum with a mean weight of 0.42 ± 0.01 mg, similar to the weight of adult X. flavipes, had an LD 50 of 15.0 μg (AI) per filter. The predator X. flavipes was 4.3- and 10.2-fold more tolerant of malathion than laboratory strains of the parasitoids Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae) and Bracon hebetor (Say) (Hymenoptera: Braconidae), respectively. F 3 -F 5 progeny of a field strain of X. flavipes collected from a bin of corn on a farm near blackville, SC, in May and June 1993 were 33-fold (males) and 31-fold (females) resistant to malathion, relative to the laboratory strain, at the LD 50 . Triphenyl phosphate, a carboxylesterase inhibitor, in combination with the LD 99 of malathion for the susceptible laboratory strain, abolished the resistance in both males and females. Larvae of T. castaneum with a mean weight of 0.37 ± 0.01 mg collected from the Blackville farm (F 2 progeny) were estimated to be 740-fold resistant to malathion. We discuss development of the naturally occurring malathion resistance in X. flavipes, a generalist predator in the stored-product ecosystem, in terms of the preadaptation and food limitation hypotheses

Toxicity of Carbaryl toward the Southern Pine Beetle in Filter Paper, Bark and Cut Bolt Bioassays

Loblolly pine bolts sprayed with 2% carbaryl (Sevimol® 40% A. I. Flowable) and 1% chlorpyrifos were exposed to southern pine beetle, Dendroctonus frontalis Zimmermann. Chlorpyrifos treatment effectively prevented attack by southern pine beetle; however, the bolts were not protected by 2% carbaryl. For the carbaryl-treated bolts, the number of egg niches and larval mines were significantly reduced. However, the number of adult beetles entering the host, the length of the parent galleries, the number of pupal chambers, brood adults, and emergence holes were not significantly (P = 0.05) different from untreated control bolts. A bark surface assay indicated that 2% carbaryl killed < 50% of the beetles at 24 h. Filter paper assay showed that the LC50 value was 0.07% and 0.01% at 24 and 48 h, respectively.

Sample Size and Temporal Variation Effects on Mortality of Colorado Potato Beetle (Coleoptera: Chrysomelidae) in a Filter-Paper Bioassay

Filter-paper bioassays were performed on Colorado potato beetles, Leptinotarsa Decemlineata (Say), collected from three commercial potato fields to determine the most cost-effective number of sample units (filter-paper disks, 10 larvae per disk). Relative net precision values from three different insecticide bioassays were used as an indication of sample-size efficiency and were based on variation in larval mortality and sample cost. Greatest sample-size efficiency in all insecticide bioassays was achieved from a sample of two to five filter-paper disk sample units (20-50 total larvae). Additional insecticide bioassays were done with Colorado potato beetle larvae collected at different times during the season (from a commercial potato field and from experiment-station plots) to determine whether the larval generation sampled or previous insecticide application affected results of the bioassay. Although trends in mortality were not always consistent among first generation larvae sampled on different dates (from insecticide-treated and untreated plots), first-generation larvae exhibited significantly greater mortality in the bioassay compared with second-generation larvae. Based on these results, it is recommended that bioassays to estimate the effectiveness of a particular insecticide against Colorado potato beetle be performed on the target generation immediately before the planned insecticide treatment.

The efficacy of linalool, a major component of freshly-milled Ocimum canum Sims (Lamiaceae), for protection against postharvest damage by certain stored product Coleoptera

Linalool was present at 8.6 ± 0.9 mg/g in the dried leaves of Ocimum canum Sims, an annual mint used in Rwanda to protect against postharvest insect damage. Direct exposure of adults of Zabrotes subfasciatus (Bohem.) to milled, dried O. canum leaves resulted in 100% mortality of males and 50% mortality of females after 48 hr. Dose-response curves for linalool were completed with adult Z. subfasciatus, Acanthoscelides obtectus (Say), Rhyzopertha dominica (F.), and Sitophilus oryzae (L.) using a filter paper bioassay. The LC 50 values were: 428 μg/cm 2 for Z. subfasciatus; 405 μg/cm 2 for A. obtectus; 428 μg/cm 2 for R. dominica; 427 μg/cm 2 for S. oryzae. Knockdown was occasionally followed by recovery at doses less than the LC 50 for all species. There are significant differences in the LC 50 and LT 50 values for male and female Z. subfasciatus. At the lower dosages hyperactivity rarely preceded moribundity and mortality where these occurred, while at higher dosages hyperactivity occurred soon after initial exposure and preceded imminent death. A concentration increase from 250 to 750 μg/cm 2, representing a tripling of dosage, spanned th 10–100% response mortality for all species at 24 hr. Air-exposure of linalool-treated papers (500 μg/cm 2) for up to 24 hr significantly decreased toxicity to both sexes of Z. subfasciatus. Quantitative analysis showed the only significant decrease in the amount of linalool to occur after 0.25 hr, and this did not fully correlate with the resulting decrease in efficacy against both sexes of Z. subfasciatus. The results are discussed in terms of the efficacy of using O. canum for the protection against loss due to insects in the traditional food storage systems of Rwanda.

Bioassay for Detecting Active Site Insensitivity in Horn Fly (Diptera: Muscidae) Larvae

A bioassay was used to detect active site insensitivity (knock-down resistance [kdr]) in pyrethroid resistant larvae of the horn fly, Haematobia irritans (L.). The larvae of the resistant population had KD50's 42.0-, 28.1- and 29.2-fold greater to permethrin, fenvalerate and lambda-cyhalothrin, respectively, compared with the susceptible population. In filter paper bioassays, resistant adult horn flies were 17 to 39.1 times less susceptible to the pyrethroids than susceptible adults at LC50. These results further document active site insensitivity as the major mechanism of pyrethroid resistance in the horn fly.

Development of a standard bioassay technique for the adults of Bemisia tabaci Gennadius (Homoptera, Aleyrodidae)

SummaryA standardized impregnated filter-paper bioassay technique was specially developed for screening insecticides against adults of the whitefly Bemisia tabaci Genn. (Homoptera, Aleyrodidae). It was found that the most suitable exposure period, after which mortality counts should be made, was 11·7 ± 2·1 h. Two different techniques for applying the insecticide solutions to the filter paper disks were tested and verified.