Electrophoretic analysis of the prey spectrum of Teretrius nigrescens (Lewis) (Col., Histeridae), a predator of Prostephanus truncatus (Horn) (Col., Bostrichidae), in Mexico, Honduras, and Benin

Abstract: Extensive collections of Teretrius nigrescens in Mexico, Honduras, and Benin, were electrophoretically analysed to elucidate the prey spectrum of the predator. Both polyacrylamide gel electrophoresis and cellulose acetate electrophoresis were used. Beetles were sampled with pheromone traps, using the synthetic aggregation pheromone of Prostephanus truncatus , and directly from farmers' maize stores. The proportion of electrophoretically detected prey protein from adult T. nigrescens in pheromone traps was low: of the 1108 specimens analysed, only in 34 cases, prey protein could be clearly identified. More frequently, prey protein was detected in adult T. nigrescens sampled in maize stores in Mexico, Honduras, and Benin, with 87 samples showing distinct prey bands of the total 1214 predators analysed. Of the 241 T. nigrescens larvae sampled in maize stores in Benin, 136 showed distinct bands of prey protein. In all samples, P. truncatus was the most frequently detected prey species. The second most often identified prey species was Sitophilus zeamais . The results are discussed with regard to various methods for prey spectrum analysis and specifically the biology of T. nigrescens .     

Optimal Xylocoris flavipes (Reuter) (Hemiptera: Anthocoridae) density and time of introduction for suppression of bruchid progeny in stored legumes

The influences of both predator density and elapsed time between initial infestation and introduction of predators were determined for suppression of bruchids infesting stored grain legumes by Xylocoris flavipes (Reuter) (Hemiptera: Anthocoridae). Predator density treatments consisted of zero, one, two, three, or five male:female pairs of adult X. flavipes added to experimental arenas 0, 24, or 120 h after bruchid introduction. Suppression of Acanthoscelides obtectus approached eradication with all predator treatments. For all other bruchid species evaluated (Callosobruchus analis, C. chinensis, C. maculatus, and Zabrotes subfasciatus), the most effective predator density and addition time (five predator pairs at 0 h) resulted in an approximately 50% reduction of emerging F1 bruchids compared with progeny produced in arenas without predators. The predator addition time of 0 h, when predators were added to experimental arenas simultaneously with the pest species, was determined to be the universally most efficacious treatment time. Predator density above one pair but lower than five pairs was less influential overall when X. flavipes was added 24 or 120 h after initial bruchid infestation; however, maximum suppression was achieved at approximately two predator pairs and not significantly improved on with increased predator density. Our results indicate that the most effective biological control of pest bruchids would occur when X. flavipes is added as soon as possible after legumes are stored.     

Studies on predation of Prostephanus truncatus (Horn) (Col., Bostrichidae) and Sitophilus zeamais Mots. (Col., Curculionidae) at different densities on maize by Teretriosoma nigrescens Lewis (Col., Histeridae)

Laboratory experiments using whole cobs were conducted to examine the effect of varying densities of the larger grain borer, Prostephanus truncatus and the maize weevil, Sitophilus zeamais on rate of population increase by the histerid beetle, Teretriosoma nigrescens , a predator primarily of P. truncatus . Densities of all species of insects were determined at the end of the experiment, and an electrophoretic analysis of gut content was conducted on larval and adult T. nigrescens sampled during the experiments. Results indicated that T. nigrescens has a strong preference for P. truncatus and densities of T. nigrescens were associated only with densities of P. truncatus . The maize weevil played little role as an alternative prey or in interfering with T. nigrescens reproduction.     

The Effects of an entomopathogenic fungus, Beauveria bassiana (balsamo) vuillemin (hyphomycetes), on Prostephanus truncatus (horn) (Col.: Bostrichidae), Sitophilus zeamais motschulsky (Col.: Curculionidae), and grain losses in stored maize in the Benin Republic

A fungal entomopathogen, Beauveria bassiana, was used to treat maize ears placed in traditional grain stores against Prostephanus truncatus in a field experiment conducted from September 1997 to March 1998 in the Benin Republic, West Africa. Treatments included oil-based spray with and without conidia, maize stored with and without the husk, and stores with and without artificial infestation. Additional treated ears kept in insect-proof cages under field conditions were sampled weekly and exposed to insects to estimate the virulence and persistence of the pathogen during the storage season. P. truncatus densities were significantly lower in treatments that included conidia, although densities were high in all artificially infested treatments and grain losses were severe. The effect of the pathogen was modeled with an exponential decay function and incorporated in a published P. truncatus simulation model. The effects of hypothetical pathogens with different virulence and persistence characteristics were evaluated in terms of insect density and percentage grain loss.     

Biological control of the larger grain borer Prostephanus truncatus (Coleoptera: Bostrichidae) in Kenya using a predatory beetle Teretrius nigrescens(Coleoptera: Histeridae)

The establishment of the predatory histerid beetle, Teretrius nigrescens Lewis, following its field release in south eastern Kenya in 1992, and its impact on populations of the larger grain borer, Prostephanus truncatus (Horn), in woodland habitats is evaluated. Pheromone trap catch data show a single strong peak of P. truncatus from November to January, coincident with the short rains. Comparisons of P. truncatus pheromone trap catches before and after predator establishment, and in areas with and without T. nigrescens, show a sustained decline of over 80% in P. truncatus abundance over a 5-year period, following the establishment T. nigrescens. Concurrent laboratory studies of the impact of T. nigrescens on populations of P. truncatus raised on a wood substrate showed a 77% reduction in the growth of the pest population. These results are compared with published findings of the impact of T. nigrescens as a biological control agent of P. truncatus in west Africa.     

Effects of kaolin on the composition of generalist predator assemblages and parasitism of Choristoneura rosaceana (Lep., Tortricidae) in apple orchards

Abstract:  In three apple orchards, we tested how the hydrophilic kaolin clay particle film Surround WP affected the diversity of generalist arthropod predator assemblages in orchard foliage and the parasitism of the pest species Choristoneura rosaceana (Harris) (obliquebanded leafroller) (Lep., Tortricidae). In two orchards, kaolin was applied to orchard foliage once a week for 4 weeks, between mid-June and mid-July in 2004 and 2005. In the third orchard kaolin was applied to foliage twice over 2 weeks in June 2004. We quantified the proportion of larvae C. rosaceana parasitized, larval populations, and the relative abundance and assemblage composition of generalist predators (spiders and insects) in the orchards. Kaolin altered the species composition of the generalist predator assemblages and reduced the relative abundances of certain generalist predators, most notably jumping and crab spiders (Salticidae and Philodromidae), assassin bugs (Reduviidae), ants (Formicidae) and coccinellids (Coccinellidae). In contrast, the relative abundances of web-spinning spiders (Araneidae, Dictynidae, Theridiidae) were not affected. Kaolin did not affect the proportion of parasitized C. rosaceana larvae, which ranged from 24% to 47% in control and kaolin treatments, or the relative proportions of parasitoid taxa. The kaolin formulation did not affect the abundance of C. rosaceana larvae, but in one orchard, kaolin did reduce the abundance of the combined numbers of C. rosaceana and another tortricid pest, Argyrotaenia velutiana . Although kaolin does not affect parasitism of C. rosaceana , it significantly changes the composition of generalist predator assemblages in orchard foliage.     

Survival of stored-product insect natural enemies in spinosad-treated wheat

The survival of stored product insect natural enemies in wheat treated with spinosad was investigated in laboratory and pilot scale experiments. The predator Xylocoris flavipes (Reuter), the warehouse pirate bug, and the parasitoids Habrobracon hebetor (Say), Theocolax elegans (Westwood), and Anisopteromalus calandrae (Howard) were exposed to wheat treated with aliquots of water or spinosad at 0.05-1 mg ([AI])/kg. X. flavipes was the only species that survived (92% survival) in spinosad-treated wheat at 1 mg/kg. X. flavipes suppressed populations of immature Tribolium castaneum (Herbst), the red flour beetle, by nearly 90% compared with a water-treated control, but 100% suppression of immatures was achieved in wheat receiving spinosad or spinosad + X. flavipes treatments. A 3-mo pilot scale experiment to evaluate T. castaneum suppression in drums holding 163.3 kg of wheat showed that the pest populations increased throughout the study in the control treatment, but peaked after 1 mo in the X. flavipes-treated drums. By comparison, better T. castaneum population suppression was achieved in spinosad or spinosad + X. flavipes treatments. Although X. flavipes can survive and reproduce in spinosad-treated wheat, under our test conditions spinosad alone provided adequate suppression of T. castaneum populations in stored wheat.     

Pest management in traditional maize stores in West Africa: a farmer's perspective

Farmers in the Republic of Benin have few resources to invest in protection of stored maize, and prophylactic pesticide application is often recommended by extension and development agencies. Neither the efficacy nor profitability of such an application in traditional maize storage facilities has been addressed quantitatively. In this study, existing management options for stored maize were evaluated monthly over 6 mo in central and southern Benin with respect to their effects on grain injury and on densities of Prostephanus truncatus (Horn) and Sitophilus zeamais Motschulsky. P. truncatus infested 54% of the experimental stores in the study even though Teretrius nigrescens (Lewis), a natural enemy introduced against P. truncatus, was well established in the region. S. zeamais was the most common pest, found in 85% of the experimental storage facilities. Prophylactically treated maize was, on average, worth more than untreated maize for month 1 through 5 in southern Benin, after taking into account market price, pesticide costs, percentage grain damage and weight loss, but maize storage was not profitable overall. No difference was observed between treatments in central Benin. After 6 mo treated storage facilities were not significantly different from untreated storage facilities in terms of either percentage damage or profit in either region. A rapid scouting plan intended to provide farmers with a means for identifying storage facilities at greatest risk of severe P. truncatus infestation was field validated. Given that unsafe pesticide use is prevalent in Benin, research and extension services should clearly state the limitations to prophylactic treatment and increase the effort to educate farmers on appropriate pesticide use, store monitoring and marketing.     

Multiple Parasitism by Cotesia sesamiae and Cotesia flavipes (Hymenoptera: Braconidae) on Busseola fusca (Lepidoptera: Noctuidae)

Busseola fusca (Fuller) is one of the most important pest of cereals in sub-Saharan Africa. Cotesia sesamiae (Cameron) is the predominant parasitoid attacking B. fusca larvae in many parts of Africa. An exotic parasitoid, Cotesia flavipes Cameron, was introduced into Kenya in 1993 for the control of Chilo partellus (Swinhoe). Laboratory studies indicated that although C. flavipes would search for, and attack B. fusca , it was not able to complete its development in this host. The aim of the present study was to investigate the outcome of multiple parasitism of B. fusca by the two Cotesia species. The study showed that when both parasitoid species stung a B. fusca larva at the same time, both parasitoids emerged from more than half of the host larvae, C. flavipes alone emerged from 17%, and C. sesamiae alone emerged from 9%. When the larvae were parasitized by C. sesamiae first, and then 2 h later by C. flavipes , and vice versa, most of the progeny were C. flavipes . However, when B. fusca larvae were stung by C. sesamiae three days before oviposition by C. flavipes , significantly more C. sesamiae emerged from the larvae. When C. flavipes oviposited first, no larvae produced C. flavipes only. The interaction of parasitoids and the host immune system, and the implications of these results for the biological control of stem borers in East Africa are discussed.     

Predation by Podisus maculiventris (Hemiptera: Pentatomidae) on Plutella xylostella (Lepidoptera: Plutellidae) larvae parasitized by Cotesia plutellae (Hymenoptera: Braconidae) and its impact on cabbage

Biological control offers potentially effective suppression of the diamondback moth (DBM), Plutella xylostella, a serious pest of Brassica crops. Little is known of whether multiple natural enemies have additive, antagonistic, or synergistic effects on DBM populations. No-choice and choice tests were conducted to assess predation by Podisus maculiventris on DBM larvae parasitized by Cotesia plutellae and unparasitized larvae. In no-choice tests, P. maculiventris preyed on greater numbers of parasitized than unparasitized larvae and greater numbers of young larvae than old larvae. In choice tests with early third instar DBM, there was no difference in predation between parasitized or unparasitized larvae. However, in choice tests with older prey, P. maculiventris preyed on more parasitized than unparasitized larvae. Two field studies were conducted to test if this predator and parasitoid have additive, antagonistic or synergistic effects on DBM populations and plant damage in cabbage (Brassica oleracea var. capitata). In 2002, DBM populations were significantly lower in the presence of C. plutellae but not in the presence of P. maculiventris. There was not a significant interaction between the natural enemies. Plant damage was reduced only with C. plutellae. In 2003, DBM populations were significantly lower in the presence of C. plutellae and P. maculiventris, although the combination of natural enemies did not lead to a non-additive interaction. Plant damage was unaffected by the presence of either natural enemy. Because of its greater predation on parasitized larvae, P. maculiventris could be an intraguild predator of C. plutellae. Yet, their overall combined effect in the field was additive rather than antagonistic.     

Predation by Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) on immature Rhagoletis mendax Curran (Diptera: Tephritidae) in semi-field and field conditions

Practices that enhance abundance and diversity of generalist predators are often employed with the objective of improving biological control of insect pests. Ground beetles and other predators can prey on blueberry maggot, an important pest of blueberries, when mature larvae pupate in the ground. We conducted mesocosm and field experiments to determine if Pterostichus melanarius, a common predatory ground beetle, lowers maggot numbers in compost mulch or when predator and alternative prey abundances are manipulated. At background (field) densities of alternative prey, increasing densities of P. melanarius did not significantly reduce pest numbers in mesocosms containing compost or soil. When alternative prey were removed from compost, beetles reduced pest numbers by up to 35%. In field experiments, maggot numbers were higher when beetles and other predators were excluded from soil plots, but beetle exclusion had no effect in compost plots where both predator and alternative prey numbers were high. Our results indicate that there can be some reduction of blueberry maggot by P. melanarius and other potential predators when there are few alternative prey. However, despite attracting large numbers of predators compost mulch did not lead to a significant reduction in blueberry maggot; in fact, the high abundance of alternative food associated with compost appeared to interfere with beetle predation on blueberry maggot.     

The effects of a winter cover crop on Diabrotica virgifera (Coleoptera: Chrysomelidae) populations and beneficial arthropod communities in no-till maize

The effects of an autumn-planted, spring-killed, grass cover crop (Elymus trachycaulus [Link] Gould ex Shinners) on populations of Diabrotica virgifera virgifera LeConte and its predator community were evaluated in South Dakota maize fields over two seasons. Abundance and size of D. virgifera larvae and adults and sex ratio of adults were measured in maize produced under two treatments (i.e., a winter cover crop or bare soil), as were maize root damage and the abundance and diversity of the predator communities collected on the soil surface and in the soil column. First and second instars and adults of D. virgifera were similarly abundant in the two treatments, but third instars were significantly fewer in maize planted after a winter cover crop. Larvae developed at different rates in the two treatments, and second instars were significantly smaller (head capsule width and body length) in the maize planted after a cover crop. First and third instars and adults were of similar size in the two treatments, and adult sex ratios were also similar. Although initially similar, predator populations increased steadily in the cover-cropped maize, which led to a significantly greater predator population by the time D. virgifera pupated. There was significantly less root damage in the cover-cropped maize. Predator communities were similarly diverse in both treatments. Predator abundance per plot was significantly and negatively correlated with the abundance of third instars per plot. Clearly, winter cover crops reduce D. virgifera performance and their damage to the crop, and we suspect that this reduction is caused by both environmental effects of the treatment on D. virgifera size and development, and of increased predation on the third instars of the pest. Additional data on the impact of cover crops on actual predation levels, grain yield and quality, and farmer profitability, and correlations among pest performance, crop characteristics, and predator populations and behaviors are key components of this system that remain to be addressed.     

Parasitus bituberosus (Acari: Parasitidae): An agent for control ofLycoriella solani (Diptera: Sciaridae) in mushroom crops

In trials conducted in a mushroom crop grown in commercial growing bags and inoculated with the dipteran pest,Lycoriella solani, and/or the predatory miteParasitus bituberosus, the mite reduced adult pest numbers ty 50–66%. It also reduced the numbers of larvalHeteropeza pygmaea, a second dipteran pest which occurred as a contaminant in one trial. Fewer mites were extracted towards the end of the cropping period. No evidence was found of an oscillating relationship between predator and prey over the trial period. Crop yield was increased by 18% and unsaleable yield was reduced by 50%. It is suggested that the mite can contribute to an integrated pest management system.     

Evaluation of sequential sampling plans for the larger grain borer (Coleoptera: Bostrichidae) and the maize weevil (Coleoptera: Curculionidae) and of visual grain assessment in West Africa

Repeated sampling of rural maize stores in Benin was conducted to evaluate published parameters of a sequential sampling plan for a negative binomial distribution to determine pest status for Prostephanus truncatus (Horn) and Sitophilus zeamais Motschulsky. A computer program was used to rerandomize the data and evaluate the effects, in terms of average sample number and error rates, of different sampling plan parameter values. With respect to P. truncatus, lower and upper thresholds of 0.2 and 1.0 insects per ear and parameter values of k = 0.2 and alpha = beta = 0.1 were found to be adequate. With respect to S. zeamais, lower and upper thresholds of 10 and 20 insects per ear and parameter values of k = 1.0 and i alpha = beta = 0.1 were found to be adequate. Simplified sampling rules were proposed in which 11 ears should be sampled and if no P. truncatus are found, the population is low; otherwise the Wald plan should be followed. Owing to the lower per capita rate of damage, effective simplified sampling rules for S. zeamais were difficult to construct. An evaluation of the visual assessment scale rising whole ears showed that a visual scale estimating percentage damage rather than percentage loss, might be easy to construct and preferable for traders. Further work is needed to improve the usefulness of the visual scale in pest management decision support.     

Infestation of maize by Prostephanus truncatus initiated by male-produced pheromone

Delta traps baited with maize cobs, which were infested each with one male Prostephanus truncatus (Horn) (Col.: Bostrichidae), were distributed in southern Benin and collected after one, two, three and four weeks. The numbers of P. truncatus caught during the different trapping periods were not significantly different. Sixty-four percent of the trapped P. truncatus were females. Females attracted during the one-week trapping period produced a mean of 6.9 progeny during the seven days. The sex ratio of the progeny was 1:1. Trap catches with the infested cobs were on average 13 times lower than catches with 2 mg of the artificial pheromone. Estimation of P. truncatus densities in a maize store at the beginning of the storage period (based on laboratory data) revealed that small initial numbers of P. truncatus, possibly attracted by a single male, sufficed to initiate high infestation rates later in the storage season.     

Phylogeographic structure of Teretrius nigrescens (Coleoptera: Histeridae) predator of the invasive post harvest pest Prostephanus truncatus (Coleoptera: Bostrichidae)

The invasive larger grain borer Prostephanus truncatus (Horn) is the most important pest of farm-stored maize in Africa. It was introduced into the continent from Mesoamerica in the late 1970s and by 2008 had spread to at least 18 countries. Classical biological control using two populations of the predator Teretrius nigrescens Lewis achieved long-term and cost effective control in warm-humid areas, but not in cool and hot-dry zones. The present study investigated the phylogenetic relationships between geographical populations of the predator. Ten populations of T. nigrescens were studied using randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR), sequence analysis of mitochondrial Cytochrme oxydase 1 (mtCOI) gene and ribosomal internally transcribed spacers (ITS) 1, 5.8S and ITS2. The mtCOI variation revealed two clades associated with geographical regions in Central America. It also reveals a significant isolation by distance between populations and considerable genetic shifts in laboratory rearing. RAPD-PCR did not reveal any potential SCAR diagnostic markers. The ITS variation mainly involved insertions and deletions of simple sequence repeats even within individuals. This study reveals the existence of two different mitochondrial lineages of the predator, associated with the geographical origin of populations distinguishable by fixed mutations on the mtCOI gene. The populations of T. nigrescens released in Africa belonged to two different clades from Meso America, namely south (released in West Africa) and north (released in eastern Africa). However, more polymorphic markers are required to clarify the observations in demographic time scales.     

Isolation and characterization of microsatellite markers from Teretrius nigrescens Lewis (Coleoptera: Histeridae), predator of the storage pest Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae)

Teretrius nigrescens is a predator of the larger grain borer (LGB) Prostephanus truncatus, an invasive post-harvest pest in Africa. We describe the isolation and characterization of 24 novel polymorphic microsatellite markers and their testing on a population from Honduras. Alleles per locus ranged between 2 and 12, and observed heterozygosity between 0.037 and 0.646. Six loci deviated significantly from Hardy-Weinberg equilibrium and showed evidence of null alleles. These markers will be useful for studies of the predator's population structure and characterizing populations for control of LGB.     

A novel 8.7 kDa protease inhibitor from chan seeds (Hyptis suaveolens L.) inhibits proteases from the larger grain borer Prostephanus truncatus (Coleoptera: Bostrichidae)

A novel trypsin inhibitor purified from chan seeds (Hyptis suaveolens, Lamiaceae) was purified and characterized. Its apparent molecular mass was 8700 Da with an isoelectric point of 3.4. Its N-terminal sequence showed a high content of acidic amino acids (seven out of 18 residues). Its inhibitory activity was potent toward all trypsin-like proteases extracted from the gut of the insect Prostephanus truncatus (Coleoptera: Bostrichidae), a very important pest of maize. This activity was highly specific, because among proteases from seven different insects, only those from P. truncatus and Manduca sexta (Lepidoptera: Sphingidae) were inhibited. This inhibitor has potential to enhance the defense mechanism of maize against the attack of P. truncatus.     

Effect of microsporidian infection in Lacanobia oleracea (Lep., Noctuidae) on prey selection and consumption by the spined soldier bug Podisus maculiventris (Het., Pentatomidae)

Abstract:  The predatory behaviour of Podisus maculiventris was investigated when this bug was presented with Lacanobia oleracea larvae infected with the microsporidian pathogen Vairimorpha necatrix . In choice tests, adult predatory bugs attacked V. necatrix -infected L. oleracea prey in similar numbers to uninfected larvae. Exposure to infected prey during nymphal development increased the rate at which adult bugs attacked diseased L. oleracea larvae. Fifth instar P. maculiventris nymphs, however, attacked infected prey in the majority of cases (>80% of occasions). Consumption of healthy and infected prey was measured for both adult and nymphal bugs. Over the course of 1 week, the mean number of V. necatrix -infected prey eaten by P. maculiventris adults (7.0 ± 0.82) was approximately twice the number of uninfected prey consumed (3.8 ± 0.42). Similarly, the number of prey larvae attacked by the bug over the course of the final nymphal stadium was also increased, with 2.9 ± 0.42 uninfected larvae eaten as opposed to 4.9 ± 0.27 V. necatrix -infected prey. However, small-scale investigations into the rate of P. maculiventris reduced small populations of L. oleracea indicated that the combination of the predator and pathogen would produce, at best, an additive effect.     

Notonomus gravis (Chaudoir) (Coleoptera: Carabidae) predation of Deroceras reticulatum Müller (Gastropoda: Agriolimacidae), an example of fortuitous biological control

The increasing use of pesticides in broad-acre cropping in South eastern Australia is suspected to have reduced native carabid beetle populations which fortuitously control potential pest populations. Slugs are increasingly becoming an establishment pest of canola, which is often attributed to stubble retention introduced to arable farming systems. Exclusion enclosures were employed to test the effect of the native carabid Notonomus gravis on the exotic pest slug Deroceras reticulatum. The native predatory species limited D. reticulatum populations and this was further supported by a negative field association between the predator and slug numbers. However, while N. gravis contributed to control of slug populations, enclosure experiments suggest that slug damage was not reduced below economic thresholds by this predator alone. Although N. gravis provides a “lying in wait” pest control option for slugs, multiple predators and environmental interactions need to be considered in developing robust integrated pest management guidelines.