Laboratory method for testing side-effects of pesticides on the rove beetleAleochara bilineata — Adults

Tests were conducted in glass cells containing moistened sand sprayed with the concentration recommended for the pesticide or with demineralised water (controls). Adult females (1–2 weeks old) ofA. bilineata were placed on the fresh residue in the cells and provided daily with fresh fly eggs as food. The duration of the test was 5 days, mortality being recorded every day. The side effects of the pesticide were expressed as reduction in egg production ofA. bilineata during the whole test period. Results permitted classification of the pesticides according to the 4 categories of harmfulness used by the IOBC working group. 23 pesticides were tested, and the reproducibility of the test appeared to be satisfactory. Generally, insecticides/acaricides had a pronounced effect on the beetles whereas fungicides and herbicides were less detrimental. Exceptions were the insecticides Tedion V 18 and Kilval, classified as harmless, and the fungicides Morestan, Pomarsol forte and Afugan rated as moderately harmful. Among growth regulators Prosevor 85 was highly detrimental while Cycocel Extra and Rhodofix had no effects. Excepting Morestan, Pomarsol forte and Ustinex PA the pesticides did not affect the hatching of eggs. The work was financed by the Danish Environmental Protection Agency.     

Historical tests of the toxicity of pesticides to Typhlodromus pyri (Acari: Phytoseiidae) and their relevance to current pest management in New Zealand apple orchards 1. Laboratory tests with eggs and larvae

A two-part review is presented relating historical tests of the toxicity of pesticides to Typhlodromus pyri and their relevance to modern pest management in New Zealand pome-fruit orchards. Over the past thirty years, the initial need for T. pyri resistance to broad-spectrum pesticides has substantially declined as a growing array of new selective chemicals have come into use. In Part 1, a laboratory bioassay is described for determining the toxicity of pesticides to the eggs and larvae of an organophosphate (OP)-resistant strain of Typhlodromus pyri from New Zealand. Apple leaves bearing T. pyri and its prey Panonychus ulmi were collected from the field. Leaf discs with known numbers of eggs (no active stages) of T. pyri and prey were cut from the leaves and sprayed with selected pesticides at recommended field rates to simulate field application. The survival of eggs, and the larvae which hatched from them, were recorded for seven days. Thirteen acaricides, 16 fungicides and 15 insecticides were evaluated. Toxic chemicals were aminocarb, amitraz, benomyl, binapacryl, chlordimeform, ethion, omethoate, oxamyl, permethrin, pirimiphos-methyl and triazophos. Slight and variable toxicity was caused by azinphos-methyl, chlorpyrifos, dinocap, mancozeb + dinocap, metiram + nitrothal-isopropyl, and sulphur. No toxicity was detected with the other 24 pesticides. A comparison of the test results with those from field trials in New Zealand showed good agreement, except that the laboratory tests failed to detect the known field toxicity of dithiocarbamate fungicides and the insecticide vamidothion. Most of the chemicals tested are no longer used in commercial pome-fruit orchards in New Zealand, all of which now practise integrated (IFP) or organic (OFP) fruit production based on selective pest management methods. The tested pesticides of continuing importance are identified, and a summary is presented of the international literature describing the impact on T. pyri of the current pesticides used in New Zealand IFP and OFP. The changes in pesticide use in New Zealand are paralleled by similar changes in most pome-fruit growing areas of the world.     

Laboratory test method to evaluate the effect of 31 pesticides on the predatory bug,Orius laevigatus (Het: Anthocoridae)

A laboratory test method was developed to evaluate the pesticide toxicity on the predatory bugOrius laevigatus (Fieber). Newly hatched first-instar nymphs ofO. laevigatus were exposed to spray deposits of pesticides that were sprayed on the glass plates of a drum cell at the manufacturer’s recommended maximum dosage. Nymphal mortality and oviposition of surviving adults were recorded. Test results of various (31) commonly used pesticides (insecticides, insecticides/acaricides, acaricides and fungicides) are presented and discussed in accord with the classification of the IOBC/WPRS Working Group ”Pesticides and Beneficial Organisms”. Most fungicides had no toxic effect on nymphal development and egg-laying of surviving adults. The acaricides tested had variable toxicity on the predatory bug, while some insect growth regulators, such as the benzoylphenyl urea were very toxic. Otherwise, the ecdysone agonist tebufenozide and azadirachtin were not harmful for nymphal development and oviposition     

Effects of 37 fungicides on the rove beetleAleochara bilineata (Col.: Staphylinidae) in the laboratory

Effects of 37 fungicides — several of which were mixtures — on adult females of the rove beetle,Aleochara bilineata, were investigated in the laboratory. The pesticides were tested in concentrations equivalent to the highest recommended dosages for practical use. Mortality, egg production and hatch of the eggs were recorded. Most fungicides had no serious effect on any of the parameters measured. Among the morpholine and dithiocarbamate fungicides, several had adverse effects on egg production and/or hatch of the eggs laid. Furthermore, chinomethionate and pyrazophos were found to be toxic at the dosages used. Results are compared to results obtained with other species of beneficial arthropods in the laboratory. The importance of including several species in the assessment of pesticide side effects as well as the importance of measuring sublethal effects are stressed.

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Résumé Des expériences de laboratoire ont été faites pour étudier les effets de 37 fongicides (dont plusieurs étaient des mélanges) sur les femelles adultes d'Aleochara bilineata. Les pesticides ont été testés à des concentrations équivalant aux plus fortes doses recommandées pour l'usage agricole. La mortalité, la production et l'éclosion des œufs ont été étudiées. La plupart des fongicides n'ont pas d'effet important sur aucun des paramètres retenus. Parmi les fongicides à base de morpholine et de dithiocarbamate, plusieurs avaient un effet contraire sur la production et l'éclosion des œufs. En outre le chinométhionate et le pyrazophos se sont révélés toxiques aux doses utilisées. Les résultats ont été comparés à d'autres résultats obtenus avec d'autres espèces d'auxiliaires au laboratoire. L'importance d'inclure plusieurs espèces dans l'évaluation des effects secondaires des pestieides ainsi que l'importance de mesurer les effets sublétaux sont soulignées.

     

Susceptibility of the eggs of the field slug Deroceras reticulatum to contact with pesticides and substances of biological origin on artificial soil

The toxicity of 14 substances, including a number of pesticides, to the eggs of the pest slug Deroceras reticulatum was determined in laboratory experiments. Eggs were kept in contact with a precisely defined artificial soil to which a range of concentrations of the test substances had been applied. Mortality of the eggs was assessed every 24 h and the median lethal doses (LD₅₀) were determined. The herbicides bromoxynil, ioxynil and pyridate + bromoxynil, the insecticides thiocyclam, diflubenzuron and azadirachtin, the molluscicides metaldehyde and methiocarb, and other compounds such as carvone, iron‐EDDHA, saponin, and an extract of Pongamia pinnata, killed the eggs after periods of exposure ranging from 2 to 14 days, depending on the compound and the dose. Only two compounds, the insecticides imidacloprid and teflubenzuron, failed to kill the eggs of D. reticulatum at any of the doses tested. Values of LD₅₀ below 0.01 mg a.i. cm^?2 were obtained for the herbicides bromoxynil, ioxynil and pyridate + bromoxynil, and for the biological pesticide azadirachtin. The feasibility of slug egg control in different contexts is discussed.     

Toxicity of pesticides used in chrysanthemum crops to eggs and nymphs of Orius insidiosus (Say) (Hemiptera: Anthocoridae)

The objective of this study was to evaluate the toxicity of some pesticides used in chrysanthemum crops to eggs and nymphs of Orius insidiosus (Say). The bioassays were carried out at 25 +/- 2 degrees C, 70 +/- 10% RH and 12h photophase. For the tests with eggs, stems of Bidens pilosa L. previously exposed to predator oviposition were dipped for five seconds in aqueous dilution of the pesticides, using 40 eggs per treatment. The pesticides were applied on nymphs using a Potter's tower. Forty first-instar and twenty second-instar nymphs of O. insidiosus were used per treatment in the tests with nymphs. The adults from eggs and nymphs treated were grouped in couples to study the pesticides effects on its reproductive parameters. None tested pesticide affected the viability of treated eggs. Azoxystrobin, benomyl, imibenconazole, iprodione, metalaxyl + mancozeb and triforine were harmless to first- and second-instar nymphs of O. insidiosus, whereas abamectin, acephate and chlorfenapyr were shown to be harmful to nymphs of both first and second instars. The pre-oviposition period, the daily number of eggs, number of eggs in ten days, and egg viability were not affected by azoxystrobin, benomyl, imibenconazole, iprodione, metalaxyl + mancozeb and triforine. These pesticides, for showing low toxicity to the predator, can be recommended in disease management programs for chrysanthemum crops, in association with O. insidiosus.     

Effects of Some Pesticides on Development of Ascaris suum Eggs

To evaluate the effects of pesticides to parasite eggs, Ascaris suum eggs were incubated with 5 different pesticides (1:1,500-1:2,000 dilutions of 2% emamectin benzoate, 5% spinetoram, 5% indoxacarb, 1% deltamethrin, and 5% flufenoxuron; all v/v) at 20℃ for 6 weeks, and microscopically evaluated the egg survival and development on a weekly basis. The survival rate of A. suum eggs incubated in normal saline (control eggs) was 90±3% at 6 weeks. However, the survival rates of eggs treated with pesticides were 75-85% at this time, thus significantly lower than the control value. Larval development in control eggs commenced at 3 weeks, and 73±3% of eggs had internal larvae at 6 weeks. Larvae were evident in pesticide-treated eggs at 3-4 weeks, and the proportions of eggs carrying larvae at 6 weeks (36±3%-54±3%) were significantly lower than that of the control group. Thus, pesticides tested at levels similar to those used in agricultural practices exhibited low-level ovicidal activity and delayed embryogenesis of A. suum eggs, although some differences were evident among the tested pesticides.     

Toxicity of some insecticides and acaricides to the predatory bugDicyphus tamaninii (Het.: Miridae)

Several pesticides were tested in the laboratory for their side-effects upon the mirid bugDicyphus tamaninii, a polyphagous predator used for IPM programmes in some vegetable crops. Residual toxicity to 3rd -4th instar nymphs on tomato leaflets was checked 24, 48 hours and seven days after treatment. The acaricides bromopropylate, dicofol+tetradifon and fenpyroximate were harmless to the nymphs. The insect growth regulators azadirachtin, buprofezin, lufenuron and pyriproxyfen were also harmless to nymphs and teflubenzuron was slightly harmful seven days after treatment. Among the conventional insecticides tested, only pirimicarb and tau-fluvalinate were harmless toD. tamaninii nymphs     

Effects of Some Pesticides on the Growth of ARF18 and Its Pathogenicity to Heterodera glycines

The effects of 22 pesticides on the mycelial growth and pathogenicity of the biocontrol fungus ARFI8 to Heterodera glycines were tested in vitro. The chemicals were added to agar at 10, 100, and 1,000 ppm a.i.; a block of agar containing the fungus was added to each test concentration; and fungal growth was measured. Subsequently, a block of the fungus on the pesticide-containing agar was used to determine the ability of the fungus to parasitize eggs of H. glycines. Aldicarb, bentazone, and chlorothalonil had little or no effect on fungal growth, whereas benomyl and thiophanate methyl completely inhibited growth of the fungus at 10 ppm. The relative insensitivity of ARF18 to certain pesticides would permit selected use of those pesticides with ARF18 in an integrated control program if the effects on the fungus in the field are similar to results from petri dish studies.     

Flight activity assessment of the egg parasitoidTrichogramma brassicae (Hym.: Trichogrammatidae) in laboratory and field conditions

A laboratory and a field test for flight initiation ofTrichogramma brassicae Bezdenko (Hymenoptera, Trichogrammatidae) (synonymous toT. maidis Pintureau et Voegele) were developed with the aim to establish a simple, cheap and quick flight quality control method forTrichogramma producers. The flight quality of four strains ofT. brassicae reared onEphestia kuehniella Zeller eggs were compared. The material tested consisted of four strains: two strains reared for two (F2) and 39 to 42 (F39–42) generations onE. kuehniella eggs without storage treatment, a diapause strain reared six generations (F6) onE. kuehniella eggs and a commercial strain also reared onE. kuehniella eggs whose production and storage conditions were unknown. Clear differences in flight activity among strains were observed. Both, the F2 and commercial strain showed significantly better flight activity under laboratory conditions compared to the other strains. Flight field cage experiments were made for comparison between field and laboratory results. Similar differences among strains in field cage experiments were observed when compared to laboratory tests.     

Sequential testing scheme for the assessment of the side-effects of plant protection products on the predatory bug Orius laevigatus

This paper describes a number of test methods, to beused in a sequential scheme, for testing the side-effects ofplant protection products on anthocorid bugs. Orius laevigatuswas used as test species. A `worst case' laboratory method wasdeveloped for evaluating the effect on mortality of the nymphsand the reproduction of the adults. An extended laboratory methodgives information on the effect of pesticides on adults undermore natural conditions. A semi-field test is executed in smallplots under field (glasshouse) conditions. Finally a field testsimulates the conditions in a commercial crop. For harmfulchemicals, both a laboratory and a semi-field persistence testwas developed to determine the safety period after which thepredatory bugs can be re-introduced in the greenhouse withoutbeing adversely affected. The total result of this sequentialscheme should indicate whether, and with what restrictions, aparticular pesticide can be implemented in IPM programs in whichO. laevigatus is used for control of western flower thrips(Frankliniella occidentalis). Twenty-two pesticides were testedincluding five fungicides, twelve insecticides and fiveacaricides. The fungicides captan, carbendazim, sulphur, thiram,tolylfluanid and the insecticides or acaricides pymetrozine,pyriproxyfen, tebufenozide and hexythiazox were harmless in the`worst case' laboratory test and thus did not need furthertesting. Imidacloprid, diafenthiuron, lufenuron, tebufenpyrad,abamectin, pyridaben and bifenthrin were harmful in thesemi-field test and should, in the tested concentrations, betternot be used simultaneously with the predatory bug. Theinsecticide dichlorvos was found harmful but short-lived in thepersistence test; it should be used before the introduction ofthe predatory bug O. laevigatus only when a safety period of 7days is respected. Pirimicarb was slightly toxic in thesemi-field test but short-lived. In IPM programs this aphicideshould be used at a low application frequency.     

Effects of 67 herbicides and plant growth regulators on the rove beetleAleochara bilineata (Col.: Staphylinidae) in the laboratory

Effects of 67 herbicides — several of which were mixtures — and plant growth regulators on adult females of the rove beetle,Aleochara bilineata, were investigated in the laboratory. The pesticides were tested in concentrations equivalent to the highest recommended dosages for practical use. Mortality, egg production and hatch of the eggs were measured. Most herbicides had no serious effect on any of the parameters recorded. Among the urea herbicides, however, several showed adverse effects on egg production and/or hatch of the eggs laid. The strongest effect was exerted by methabenzthiazuron that impeded hatch of the eggs completely. Bromoxynil, pyridate and haloxyfod reduced survival, egg production and/or egg hatch to some degree, while carbaryl, which is also used as a plant growth regulator, killed all the beetles immediately. The usefulness of dose-response-studies and the importance of measuring sublethal effects are stressed, and the choice of herbicides showing no toxic effects is recommended.

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Résumé Des expériences ont été faites au laboratoire pour tester les effets de 67 herbicides — dont plusieurs étaient des mélanges — et régulateurs de croissance des plantes sur les femelles adultes d'Aleochara bilineata. Les pesticides ont été testés à des concentrations équivalant aux dosages les plus élevés recommandés pour l'usage agricole. La mortalité, la production et l'éclosion des oeufs ont été mesurés. La plupart des herbicides n'ont pas d'effet important sur aucun des paramètres retenus. Parmi les herbicides à base d'urée cependant, plusieurs montrent des effets négatifs sur la production d'oeufs et/ou l'éclosion des oeufs. L'effet le plus fort a été provoqué par le métabenzthiazuron qui empêchait complètement l'éclosion des oeufs. Le bromoxynil, le pyridate et l'haloxyfop réduisaient la survie, la production d'œufs et/ou, jusqu'à un certain point, l'éclosion des œufs. Le carbaryl par contre, qui est aussi employé comme régulateur de croissance des plantes, tuait immédiatement tous les staphylins. L'utilité des études dose-réponse et l'importance de mesurer les effets sublétaux sont soulignés; le choix des herbicides ne montrant pas d'effet toxiques est recommandé.

     

A method to assess the effects of pesticides on the predatory mite Phytoseiulus persimilis (Acari Phytoseiidae) in the laboratory

Phytoseiulus persimilis Athias-Henriot (Acari Phytoseiidae) is a major predator of Tetranychus urticae (Acari Tetranychidae). The performance of P. persimilis in controlling T. urticae may be altered by pesticides used to manage other pests. Therefore, knowledge of the side-effects of pesticides is essential for IPM. A number of laboratory methods were suggested to evaluate pesticide side-effects on predatory mites. Most methods assess residual effects only, and a number of them are characterised by high predator escape rates from experimental units. A method aimed at evaluating the topical and residual effects of pesticides on P. persimilis is herein described. Mites were treated by microimmersion and then reared in holding cells, on bean leaves previously dipped in a pesticide solution. Three insecticides (pyrethrins, spinosad and thiamethoxam), an insecticide-acaricide (abamectin), and two fungicides (azoxystrobin and tolylfluanide) were evaluated. The strain of P. persimilis used for evaluation was collected from unsprayed vegetable plants. All the pesticides affected the survival and fecundity of P. persimilis. Pesticides did not affect the egg-hatching of P. persimilis females exposed to pesticides. Pyrethrins and abamectin proved to be more toxic than other pesticides, and thiamethoxam was more toxic than spinosad, azoxystrobin and tolylfluanide. The escape rate from experimental units was lower than 5% in all trials. Additional experiments were performed on P. persimilis eggs by dipping leaves with eggs in the pesticide solution. None of the pesticides affected egg survival. Semi-field trials conducted on potted bean plants obtained results similar to those reported in laboratory trials.     

Synchrony in the hatching of eggs in the desert locust <Emphasis Type="Italic">Schistocerca gregaria</Emphasis> (Orthoptera: Acrididae): egg condition influences hatching time in the laboratory and under simulated field temperatures

This study examined the time of hatching of the desert locust Schistocerca gregaria Forskål (Orthoptera: Acrididae) in the laboratory to test the effect of eggs within a pod versus individualized eggs. The pod organization of eggs is thought to play a role in controlling hatching time and to facilitate synchronous hatching at constant temperatures. In the present study, we examined the hatching times of eggs in a pod and individualized eggs under 24-h thermocycles and simulated field temperatures. We tested two patterns of thermocycles consisting of a 12-h thermoperiod (35 or 30 °C) and 12-h cryoperiod (low temperature period; 30 or 25 °C), and two patterns of field temperatures observed in a natural habitat, Mauritania, in May and September. The majority of eggs hatched during low temperature periods in all patterns tested. In addition, the variances of hatching times for individualized eggs were significantly greater than for egg pods in which a clear peak of time of hatching was observed. We show that egg condition influences hatching time under thermocycles of constant and fluctuating temperatures in the laboratory, and may play a role in the adaptive time of hatching.     

Pesticide Susceptibility of Two Coccinellids (Stethorus punctum picipes and Harmonia axyridis) Important in Biological Control of Mites and Aphids in Washington Hops

The susceptibility of Stethorus punctum picipes (Casey) and Harmonia axyridis Pallas larvae to pesticides used or with potential for use in Washington hops, was examined in laboratory bioassays. All pesticides tested except the miticide, hexythiazox, the insecticides, chlorpyrifos and pirimicarb, and the fungicide, mycobutanil, produced 100% mortality in S. punctum picipes at concentrations equivalent to field rates. The insecticides, pirimicarb, endosulfan, and thiamethoxam were least toxic to H. axyridis. Bifenthrin, diazinon, dimethoate, methomyl, carbaryl, malathion, phosmet, imidacloprid, and chlorpyrifos were highly toxic. The miticides, abamectin and fenpyroximate were highly toxic, milbemectin was moderately toxic but all other miticides tested were non-toxic. All fungicides had low toxicity. Selection and use of pesticides compatible with natural enemies and conservation biological control in Washington hop production is discussed.     

A standardized method for testing the side effects of pesticides on the predacious mite,Amblyseius potentillae [Acarina: Phytoseiidae]

A method is described for testing adverse effects of pesticides on the predacious miteAmblyseius potentillae Garman in the laboratory. It complies with the terms of the W.P.R.S./I.O.B.C. Working Group “Pesticides and Beneficial Arthropods” with respect to such methods. Twenty commercial pesticides were tested on the predator as part of a joint pesticide test programme of the Working Group.     

Effects of pesticides commonly used in peach orchards in Brazil on predatory lacewing <Emphasis Type="Italic">Chrysoperla carnea</Emphasis> under laboratory conditions

Effects of the maximum field recommended concentration of five pesticides currently used on peaches in Brazil; abamectin, deltamethrin, methoxyfenozide, phosmet and trichlorfon were tested on the predator Chrysoperla carnea (Stephens) (Neuroptera, Chrysopidae). Dimethoate was used as positive standard. Three analytical laboratory tests, based on IOBC—working group pesticides and beneficial organisms guidelines were used: (1) exposure to fresh pesticide residue on glass plates of (a) larvae (susceptible life stage) and (b) adults (less susceptible life stage); (2) direct spraying of eggs and pupae; (3) exposure of larvae and adults to pesticide residues on plant leaves at different intervals after application (persistence). In tests 1, abamectin was slightly harmful to C. carnea larvae and phosmet and trichlorfon were slightly harmful and moderately harmful to C. carnea adults, respectively. After direct spraying of eggs and pupae, all the pesticides were harmless. In the persistence tests, abamectin and trichlorfon were classified as short lived and therefore they could be considered for use in Integrated Pest Management (IPM) programs under special conditions (i.e. reduced direct contact). Phosmet, however, caused between 56.3 and 75.0% mortality up to 30 days after treatment and it was rated as persistent. No sublethal effects were detected in the reproductive behaviour of adults (fecundity and fertility) compared with the control in any treatment. In conclusion, the insecticides with little or no toxicity to C. carnea such as abamectin, deltamethrin and methoxyfenozide could be considered as IPM-compatible, subject to further field studies.     

Historical tests of the toxicity of pesticides to Typhlodromus pyri (Acari: Phytoseiidae) and their relevance to current pest management in New Zealand apple orchards 2. Short-term field tests

A two-part review is presented relating historical tests of the toxicity of pesticides to Typhlodromus pyri and their relevance to modern pest management in New Zealand pome-fruit orchards. Over the past 30 years, the initial need for T. pyri to be resistant to broad-spectrum pesticides has substantially declined as a growing array of new selective chemicals have come into use. In Part 2, a short-term field test is described for determining the toxicity of single applications of pesticides at recommended rates to European red mite (ERM), Panonychus ulmi, and its predator, an organophosphate (OP)-resistant strain of T. pyri on apples in New Zealand. For each pesticide, changes in mite density were measured from pre-treatment to 2, 7 and up to 25 days post-treatment compared with a water-sprayed control. Density was recorded and analysed for live adult and immature ERM, and live and dead eggs, larvae, nymphs and adults of T. pyri. Fifteen acaricides, 17 fungicides and 17 insecticides were evaluated. Chemicals more toxic to T. pyri than ERM were aminocarb, amitraz, binapacryl, chlordimeform, etrimphos, fenvalerate + azinphos-methyl, mancozeb + dinocap, methidathion, methiocarb, omethoate, oxamyl, pirimiphos-methyl and pyrazophos. Chemicals equally or less toxic to T. pyri than to ERM were acequinocyl, azocyclotin, benzoximate, bromopropylate, chlorpyrifos, clofentezine, cycloprate, cyhexatin, dinocap, mineral oil, propargite, triazophos and vamidothion. The remaining 23 chemicals (primarily fungicides and OP insecticides) had slight or no toxicity to ERM and T.pyri. The short-term field tests provided a useful guide to the long-term effects on ERM and T. pyri populations of almost all the pesticides. However, the potential disruptive effect of pyrazophos was not found in long-term field trials, and conversely, the apparently harmless dithiocarbamate fungicides were later shown to be highly disruptive when repeatedly sprayed, as in commercial practice. Most of the chemicals tested are no longer used in commercial pome-fruit orchards in New Zealand, all of which now practise integrated fruit production or organic fruit production based on selective pest management methods. The tested pesticides of continuing importance are identified and discussed with special emphasis on the current need to retest for dithiocarbamate resistance in T. pyri, some populations of which have been exposed to these compounds for up to 40 years. This and the changes in pesticide use in New Zealand are paralleled by similar developments in most pome-fruit growing areas of the world.     

Fragmentation in the clouds? The population genetics of the native bee <Emphasis Type="Italic">Partamona bilineata</Emphasis> (Hymenoptera: Apidae: Meliponini) in the cloud forests of Guatemala

Habitat fragmentation and loss are important drivers of genetic differentiation, often leading to a decrease in genetic diversity. Yet, natural populations of tropical bees often show a lack of differentiation, even in fragmented landscapes, suggesting resilience to deal with unfavourable land use. It is not clear what leads to this lack of differentiation, but large population sizes, high rates of dispersal and stable demography likely play important roles. Here, we investigate the population genetic structure and infer the present and historic demography of the eusocial stingless bee Partamona bilineata from tropical montane cloud forests in Guatemala. We used microsatellites and mitochondrial DNA to test for genetic differentiation, to infer migration rates, and to evaluate the effects of landscape. We also used demographic modelling to trace population sizes over time. We found that six populations of P. bilineata exhibited only subtle differentiation, with the exception of one site at the edge of the cloud forest, which was clearly distinct from all others. Effective population sizes (number of colonies) appeared to be rather small (18?±?6 colonies) compared to the original sample size (N?=?51?±?9), but stable over time, and inferred rates of gene flow were low; yet, no genetic bottleneck was detected. A statistical model including elevation was the best in explaining the observed pattern of differentiation. We find that P. bilineata does not exhibit strong genetic structure, making it a resilient species for provision of pollination services. But, at the same time, our data point to the potential vulnerability of this and similar species, as effective population sizes appear to be low and hence populations may be easily affected by future environmental change. As such, P. bilineata may be representative of many other tropical stingless bees, for which lack of differentiation has been invoked.     

Responses of the parasitoids of Delia radicum (Diptera: Anthomyiidae) to the vegetational diversity of intercrops

Several natural enemies regulate populations of root maggots (Delia spp.) (Diptera: Anthomyiidae) in canola (Brassica napus L.) in western Canada, among them the rove beetles Aleochara bilineata Gyllenhal and Aleochara verna Say (Coleoptera: Staphylinidae) and the hymenopteran Trybliographa rapae Westwood (Hymenoptera: Figitidae). Intercrops of canola and wheat (Triticum aestivum L.) can be part of an integrated pest management strategy to reduce damage by Delia spp. to canola. We investigated several intercropping regimes of canola and wheat to determine effects on parasitism of Delia radicum (L.) and activity densities of adult A. bilineata and A. verna. Studies were conducted over four site-years in central Alberta, Canada in 2005 and 2006. Mean parasitism rates of D. radicum puparia by A. bilineata ranged from 7.27% to 81.69%. Increasing proportions of wheat in intercrops significantly reduced parasitism by A. bilineata in one site-year. Parasitism of D. radicum by T. rapae was not affected by intercropping; mean parasitism rates were between 2.17% and 14.55%. In one site-year combined parasitism by all parasitoids significantly increased with increasing canola as a proportion of total crop plant populations. Pitfall trap collections of adult A. bilineata increased with increasing proportions of canola in some site-years. Collections of A. verna adults were low relative to A. bilineata and were largely unaffected by intercropping. Although canola–wheat intercrops do not appear to favour parasitism of D. radicum, reductions in canola root damage by Delia larvae in intercrops, reported previously, suggest that canola–wheat intercrops may nevertheless be favourable as a crop protection strategy.