Predatory response of Xylocoris flavipes to bruchid pests of stored food legumes

Biological control may provide an affordable and sustainable option for reducing losses to pest Bruchidae in stored food legumes, a crucial source of human dietary protein. Previous investigations have focused primarily on the role of parasitism in bruchid biological control, while the potential of generalist predators has been comparatively unexplored. The true bug Xylocoris flavipes (Reuter) (Heteroptera: Anthocoridae) exhibited a Type II functional response to the majority of cosmopolitan bruchid species evaluated when data were fit to Holling's disc equation. A negative correlation was detected between mean pest species body weight and rate of predation. The rate of attack on adult prey was quite low but fairly consistent, with the larger‐sized female predators generally more effective. The eggs and neonate larvae of Acanthoscelides obtectus Say (Coleoptera: Bruchidae) were the only accessible immature stages among all prey species examined; predation on A. obtectus eggs and larvae was higher than on any adult bruchids. Mean predator kill of A. obtectus immature stages was 40 first instars or 10–20 eggs per 24‐h interval. Further investigation of the biological control potential of X. flavipes against pest Bruchidae is merited due to the predator's ability to kill adult stages of all prey species evaluated.     

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.     

Efficacy of Xylocoris flavipes (Reuter) (Het., Anthocoridae) to suppress Prostephanus truncatus (Horn) (Col., Bostrichidae) in traditional maize stores in southern Togo

In the course of three storage periods (1988–90) the predacious insects that occur in traditional maize stores in southern Togo were observed and their relationship to the introduced pest Prostephanus truncatus was investigated. The bug Xylocoris flavipes , a predator on a wide range of post-harvest pests, was the only one observed regularly and in higher numbers. Laboratory trials with P. truncatus showed that the larvae were preyed on, and no preference for any one of the three instars was detected. On average, 7.3 pest larvae were killed by larvae or adults of the predator. In glass jar trials on loose maize X. flavipes reduced the numbers of P. truncatus by 57.6% after 8 weeks. The losses and damage were reduced by 50 and 17.6%, respectively. Observations in traditional maize stores indicated a tendency to decreasing populations of X. flavipes when populations of P. truncatus increased, presumably due to the unfavourable environmental conditions created by the pest. Therefore, it is concluded that X. flavipes does not play an important role in the control of this pest.     

Use of micro-CAT scans to understand cowpea seed resistance to Callosobruchus maculatus

The cowpea bruchid, Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchini), is a worldwide pest of stored cowpea grain [ Vigna unguiculata (L.) Walp. (Leguminosae)], causing tens of millions of dollars' worth of damage annually. One method of managing this pest involves planting cultivars whose seeds are resistant to bruchids. Despite extensive research, we still do not know the mechanism by which TVu 2027, the original resistant cowpea line, resists C. maculatus . Using micro-CAT (computerized axial tomography) scan imaging, we visualized the feeding patterns of bruchids living and growing within cowpea seeds. We present evidence that an interior zone in TVu 2027 seeds is responsible for the high mortality and developmental delays experienced by avirulent larval bruchids. We observed that both virulent as well as avirulent bruchid strains have different feeding patterns in TVu 2027 seeds compared to susceptible seeds. It appears that the resistance factor is most concentrated in a zone in each cotyledon adjacent to the air space separating the two seed halves.     

Conservation of native fauna in highly invaded systems: managing mammalian predators in New Zealand

Programs to conserve native fauna in invaded ecosystems often aim to reduce the impacts of alien predators. This approach can lead to unexpected outcomes in the native and the remaining invasive components of restored ecosystems. In New Zealand, suppression and eradication of invasive mammalian predators are well‐established conservation strategies, particularly on offshore islands and in mainland ecosanctuaries. Predator control has achieved important conservation gains over increasingly large areas but these can be offset by the ecological release of other uncontrolled pest species. In addition, novel ecosystems created by selective predator control and reintroductions of locally extinct or depleted native species may have unexpected trajectories as they evolve. Effective conservation requires new techniques for controlling entire suites of invasive predators over large areas, routine monitoring of the conservation outcomes of predator control, and better understanding of how modified, and in some cases reconstructed, seminatural ecosystems change when invasive predators are removed.     

多物种共存系统中3种蜘蛛对褐飞虱的控制作用

选择稻田生态系统中天敌蜘蛛优势种食虫沟瘤蛛（Oedothorox insecticeps)、拟水狼蛛（Pirata subpiraticus)、粽管巢蛛（Clubiona japonicola)和水稻主要害虫飞虱（Nilaparvata lugenis)组成多物种共存系统,运用二次通用旋转组合设计统计方法探讨多种蜘蛛对1种稻虫的控制作用,分析天敌之间以及天敌与害虫之间的相互作用关系,得出了天敌对害虫的捕食量模型2个。对模型进行主次分析表明,害虫自身密度的大小对天敌的捕食量影响较大。天敌中对捕食量作用最大的是粽管巢蛛,其次是拟水狼蛛,食虫沟瘤蛛的作用稍小。分析天敌间的交互作用表明,天敌个体大、活动能力强、生态位窄及其重叠值高、捕食量大,它们的种内种间干扰程度也大,特别是粽管巢蛛的种内干扰、拟水狼蛛和粽管巢蛛的种间干扰作用十分明显。最后讨论了天敌蜘蛛能有效控制害虫的最大密度,以及在该害虫密度下各种天敌密度的最佳组合。     

Bruchid (Coleoptera: Bruchidae) ovicidal phenylbutanoid from Zingiber purpureum

The larvicidal activity of the dichloromethane extract of Zingiber purpureum Roscoe (Zingiberaceae) rhizome against the second instar of Aedes aegypti (L.) (Diptera: Culicidae) is shown to be due to 4-(3',4'-dimethoxyphenyl)buta-1,3-diene. The diene also showed ovicidal activity against the bruchid Callosobruchus maculatus (F.) (Coleoptera: Bruchidae). Most of the eggs laid by bruchids on treated cowpea seeds were transparent, and very few of them contained developing embryos. The few larvae produced from these embryos were unable to penetrate the seed coat and enter the seed. Similar effects were seen when adults were exposed to the compound and then placed on untreated cowpea seeds, suggesting that a new type of maternally mediated ovicidal effect was involved. Coated and impregnated granular formulations of the extract were evaluated for use in the control of bruchid infestation of stored cowpea seeds. Coated granules showed activity similar to that of the crude extract but were found to lose activity rapidly. Impregnated granules were found to be less active than the crude extract.     

Characterization of digestive enzymes of bruchid parasitoids-initial steps for environmental risk assessment of genetically modified legumes

Genetically modified (GM) legumes expressing the α-amylase inhibitor 1 (αAI-1) from Phaseolus vulgaris L. or cysteine protease inhibitors are resistant to several bruchid pests (Coleoptera: Chrysomelidae). In addition, the combination of plant resistance factors together with hymenopteran parasitoids can substantially increase the bruchid control provided by the resistance alone. If the strategy of combining a bruchid-resistant GM legume and biological control is to be effective, the insecticidal trait must not adversely affect bruchid antagonists. The environmental risk assessment of such GM legumes includes the characterization of the targeted enzymes in the beneficial species and the assessment of the in vitro susceptibility to the resistance factor. The digestive physiology of bruchid parasitoids remain relatively unknown, and their susceptibility to αAI-1 has never been investigated. We have detected α-amylase and serine protease activities in all five bruchid parasitoid species tested. Thus, the deployment of GM legumes expressing cysteine protease inhibitors to control bruchids should be compatible with the use of parasitoids. In vitro inhibition studies showed that sensitivity of α-amylase activity to αAI-1 in the parasitoids was comparable to that in the target species. Direct feeding assays revealed that harmful effects of α-amylase inhibitors on bruchid parasitoids cannot be discounted and need further evaluation.     

Field boundaries of Panicum maximum as a reservoir for predators and a sink for Chilo partellus

Abstract:  The biological-control function of field boundaries of Guinea grass, Panicum maximum Jacq. on the spotted stem borer, Chilo partellus Swinhoe was examined as a reservoir for arthropod predators and as a trap plant for the pest. Field border vegetation and predator density were manipulated to determine the effect of the grass border on the abundance of stem borers and their predators in maize fields, and the effect of predators on the stem borer population. The strip of Guinea grass supported an abundance of earwigs and spiders, the potential predators of stem borer eggs and larvae. Density of C. partellus larvae in the Guinea grass strips was low throughout the season and only young larvae were collected, suggesting the inferiority of the grass stand as a habitat for stem borer larvae. These results indicate that Guinea grass is a good agent of habitat management to selectively enhance arthropod predators of stem borers and act as a sink for the pest. Predator removal resulted in a higher density of C. partellus than control in maize-bordered plots. On the other hand, no difference was found in the stem borer density between predator treatments in grass-bordered plots, probably because of insufficient predator reduction in removal plots. These results suggest that the predator assemblage found in the study site has, if sufficiently abundant, potential to limit the C. partellus population in maize fields. Even though the Guinea grass stand harboured an abundant number of predators, the grass boundaries around maize fields did not enhance predator populations within the crop field. Furthermore, field boundaries of Guinea grass had no measurable effect on the within-field density of C. partellus as a trap crop. Creating a polyculture within the crop and early planting of the grass could further enhance the biological-control function of Guinea grass boundaries.     

Suppression of the stored-product insect Tribolium confusum by Xylocoris flavipes and Amphibolus venator

Abstract:  We evaluated the suppression of the confused flour beetle, Tribolium confusum , by the anthocorid bug Xylocoris flavipes and the reduviid bug Amphibolus venator . Four treatments were tested: X. flavipes adults, A. venator adults, X. flavipes adults and A. venator adults released, and control (no predators). After 25 days, X. flavipes alone showed 96.9% suppression of T. confusum , A. venator alone showed 76.2% suppression and both the predatory bugs together showed 95.6% suppression. The rates of loss of whole-wheat flour as an index of damage caused by T. confusum were 2.7%, 6.4%, 3.6% and 11.7% in X. flavipes adults, A. venator adults, X. flavipes adults and A. venator adults released, and control respectively. Furthermore, A. venator attacked X. flavipes adults but not X. flavipes nymphs. The possibility of using both X. flavipes and A. venator against T. confusum is discussed.     

No evidence of nonlinear effects of predator density,refuge availability,or body size of prey on prey mortality rates

Predator density, refuge availability, and body size of prey can all affect the mortality rate of prey. We assume that more predators will lead to an increase in prey mortality rate, but behavioral interactions between predators and prey, and availability of refuge, may lead to nonlinear effects of increased number of predators on prey mortality rates. We tested for nonlinear effects in prey mortality rates in a mesocosm experiment with different size classes of western mosquitofish (Gambusia affinis) as the prey, different numbers of green sunfish (Lepomis cyanellus) as the predators, and different levels of refuge. Predator number and size class of prey, but not refuge availability, had significant effects on the mortality rate of prey. Change in mortality rate of prey was linear and equal across the range of predator numbers. Each new predator increased the mortality rate by about 10% overall, and mortality rates were higher for smaller size classes. Predator–prey interactions at the individual level may not scale up to create nonlinearity in prey mortality rates with increasing predator density at the population level.     

Effects of alternative food on cannibalism and herbivore suppression by carabid larvae

1. Predator and alternative food density are important factors influencing herbivore suppression by generalist predators. Herbivore suppression can be reduced if predators forage preferentially on alternative foods. Cannibalism can increase at high predator densities, further reducing herbivore suppression. However, complex interactions are possible, as alternative food can increase predator abundance and survival restoring top‐down effects on herbivores. 2. In two species of carabid larvae (Poecilus chalcites and Anisodactylus ovularis), we studied how alternative foods (fly pupae and grass seeds) and predator density affect predation of black cutworm larvae and how alternative foods affect cannibalism among carabid larvae. 3. Adding alternative food to microcosms generally reduced total predation of cutworms. However, the strength of this effect was dependent on carabid species, larval density, and food type. 4. Increasing larval density from one to three per microcosm reduced per‐capita predation by both species irrespective of alternative food treatment. 5. Alternative food reduced cannibalism in both carabid species and increased survival of carabid larvae in field plots, such that twice as many were captured in plots subsidised with pupae than plots with no alternative food. 6. These results provide new insight into the complex interactions that influence predator survival and herbivore suppression in resource diverse habitats by demonstrating the primacy of intraguild interactions among carabid larvae.     

Testing prey DNA fingerprinting on Amblyseius largoensis (Acari: Phytoseiidae) predation of Raoiella indica (Acari: Tenuipalpidae)

Molecular detection of predation by identifying prey markers in the digestive tract of predators has developed into a powerful tool to assess predator-prey systems in which diet identification is too time consuming or impossible. Here we explore its utility for detecting predation of the pest mite Raoiella indica Hirst by the predatory mite Amblyseius largoensis Muma, taking advantage of the color the predator acquires after eating this mite to cross-reference our results. For this, a ~410?bp segment of the cytochrome c oxidase subunit I (COI) mitochondrial gene marker specific for the subfamily Tetranychoidea was used. Amblyseius largoensis that had recently eaten were collected from greenhouse colonies containing both mites, and isolated from any other food source. Predator mites were taken for fingerprinting at 24, 48, 72 and 96?h of starving after collection, and the same process was repeated a second time, offering pollen as an alternative food source to see whether detection changed. Lastly, a sampling trial was conducted in the greenhouse, in which mites were collected regardless of their color and frozen immediately for fingerprinting. Raoiella indica DNA was detected for 48 h on starving predators, and for 96 h on those who had eaten pollen. The segment was detected in 26?% of the samples collected on the trial. This technique needs refinement specific for this system, but the results obtained here confirm that it could turn into a very useful tool for assessing aspects of this predator-prey system.     

Relationships between insect predator populations and their prey,Thrips tabaci,in onion fields grown in large-scale and small-scale cropping systems

Onion thrips, Thrips tabaci Lindeman, is the primary pest of onion, which is grown in either large-scale, monoculture systems surrounded by other onion fields, or in small-scale systems surrounded by multiple vegetable crops. In 2011 and 2012, populations of insect predators and their prey, T. tabaci, were assessed weekly in onion fields in both cropping systems. Insect predator taxa (eight species representing five families) were similar in onions grown in both systems and the most commonly occurring predators were from the family Aeolothripidae. Seasonal population dynamics of predators and T. tabaci followed similar trends within both cropping systems and tended to peak in late July and early August. Predator abundance was low in both systems, but predator abundance was nearly 2.5 to 13 times greater in onion fields in the small-scale system. T. tabaci abundance often positively predicted predator abundance in both cropping systems.     

Interaction of the temperature with the parasite mite Acarophenax lacunatus (Cross & Krantz) (Prostigmata: Acarophenacidae) on the development of Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae)

The objective of this study was to evaluate the effect of different temperatures with the association of the mite Acarophenax lacunatus (Cross & Krantz) on the population suppression of Rhyzopertha dominica (Fabricius). The experimental units were petri dishes containing 40 g of whole wheat grains (13% moisture content) infested with 10 adults of R. dominica, under the temperatures of 20, 25, 30 and 35 masculineC, with or without A. lacunatus, in five replicates. Relative humidity of 60 +/- 5% and escotophase of 24h were used for all temperatures. Five days after the infestation, five mites were inoculated in each experimental unit. The evaluations were carried out at 20, 40, 60, 80, 100 and 120 days after R. dominica infestation. The interaction of the temperature with the parasite A. lacunatus was an important tool for the population suppression of R. dominica. In temperatures higher than 25 masculineC, however, despite the reduction of the immature stages of R. dominica, there was a high grain weight loss after 120 days. The maintenance of the temperature of the wheat grains stored at 20 masculineC can be used to complement the biological control of R. dominica with A. lacunatus.     

Bruchid pest management in pulses: past practices,present status and use of modern breeding tools for development of resistant varieties

Bruchids (Callosobruchus spp.) are recognised as the most detrimental storage pest of pulses, especially in the tropics and subtropics. They invade matured pods as well as seeds during storage and, to some extent, farming fields, in turn reducing the net yield of the crops. Several approaches including cultural, biological, physical and chemical control measures have been implemented with the aim of managing these pests, but none of these have been successful across time and space. Recently, transgenic‐ and marker‐assisted breeding approaches have appeared as promising tools for the successful management of these pests. Although some efforts have been made on the development of bruchid‐resistant transgenic crops, the cultivars developed are yet to be commercialised worldwide because of various limitations. In contrast, marker‐assisted breeding involving the identification of DNA‐based markers linked to host resistance against bruchids, have shown some success in the quest for the development of bruchid‐resistant cultivar(s). DNA markers linked to bruchid resistance have been identified in various grain legumes, particularly in the genus Vigna, and include mung bean (Vigna radiata), azuki bean (Vigna angularis), rice bean (Vigna umbellata), cowpea (Vigna unguiculata) and black gram (Vigna mungo). After their validation in different genetic backgrounds, these markers could be utilised for marker‐assisted selection and breeding ventures to protect pulse crops. The present study discusses the pros and cons of different approaches for the successful management of the bruchid pests in pulses. The review also highlights about the integrative approach aided with molecular interventions to improve productivity by avoiding losses incurred due to bruchids, and to attain sustainable yields for major pulse crops.     

Competitive interactions among two specialist predators and a generalist predator of hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae) in south-western Virginia

1 Competitive interactions among two specialist predators, Laricobius nigrinus and Sasajiscymnus (Pseudoscymnus) tsugae, and a generalist predator, Harmonia axyridis Pallas, of hemlock woolly adelgid, Adelges tsugae were evaluated in hemlock stands in south‐western Virginia. The two specialist predators are part of a biological control program for A. tsugae, and the potential for competition among these species and previously established generalist predators in the field is unknown. 2 Adult predators were evaluated in branch cages during spring and summer at two field sites infested with A. tsugae. Using females only in 2003 and sexual pairs in 2004, predator survival and net reproduction were examined, as well as their feeding and impact on A. tsugae when present alone and in conspecific and heterospecific groupings. 3 Predator survival was not affected by the presence of additional predators. Total feeding was greater for all species when placed in predator groupings, suggesting that interactions do not significantly interfere with feeding activity. Net reproduction per predator was negatively affected by conspecifics, but unaffected by heterospecifics, indicating that direct or indirect intraspecific interference may occur. In spring, L. nigrinus showed the greatest impact on A. tsugae, and H. axyridis had the greatest impact during summer. 4 These results suggest that it would be beneficial to utilize multiple predator species combinations over single species when implementing biological control for A. tsugae. Low‐density releases are also recommended to reduce intraspecific interference.     

Effect of tomato leaf hairiness on functional and numerical response of Neoseiulus californicus (Acari: Phytoseiidae)

The objective of this study was to determine whether differences in hairiness of tomato plants affect the functional and numerical response of the predator Neoseiulus californicus McGregor attacking the two-spotted spider mite, Tetranychus urticae Koch. Two tomato hybrids with different density of glandular hairs were used. The functional response was measured by offering eggs and adults of T urticae at densities ranging from 4 to 64 items per tomato leaflet (surface ca. 6.3 cm2); eggs were offered to predator protonymphs and deutonymphs, adult spider mites to adult predators. The number of spider mites eaten as a function of initial density was fitted to the disc equation. Predator densities were regressed against initial prey densities to analyze the numerical response. The number of eggs and adults of T. urticae eaten by N. californicus was extremely low in both hybrids. The nymphal stage of N. californicus and prey density had a significant effect on the number of T urticae eggs eaten by the predator, while hybrid had no effect. The functional response fitted reasonably well to the Holling model. The handling time (Th) and the attack rate (a) were very similar among the two hybrids. The numerical response indicated that the absolute density of predators increased with changes in spider mite densities but the relative predator/prey density decreased in both hybrids. Tomato hairiness prevented N. californicus from exhibiting a strong numerical response and the predator functional response was much lower than observed in other host plants and other phytoseiids. This result shows the need to consider plant attributes as an essential and interactive component of biological control practices.     

Mapping of quantitative trait loci for a new source of resistance to bruchids in the wild species Vigna nepalensis Tateishi & Maxted (Vigna subgenus Ceratotropis)

Azuki bean breeders have long been interested in producing azuki bean [Vigna angularis (Willd.) Ohwi & Ohashi] varieties with bruchid resistance. A new bruchid (Callosobruchus spp.) resistance source was found in V. nepalensis Tateishi & Maxted, a species that is cross compatible with azuki bean. Quantitative trait loci (QTLs) analysis for resistance to C. chinensis (L.) and C. maculatus (F.) was conducted using F(2) (V. nepalensis x V. angularis) and BC(1)F(1) [(V. nepalensis x V. angularis) x V. angularis] populations derived from crosses between the bruchid resistant species V. nepalensis and bruchid susceptible species V. angularis. Resistance was measured using two traits, percentage of seeds damaged by bruchids and the time taken for adult bruchids to emerge from seeds. Based on the results from both populations seven QTLs were detected for bruchid resistance; five QTLs for resistance to C. chinensis and two QTLs for resistance to C. maculatus. The different locations found for some resistance QTL to the two bruchid species suggests different resistance mechanisms. QTLs on linkage group (LG) 1 and LG2 for bruchid resistance to C. chinensis co-localized with seed size QTLs suggesting that incremental increase in seed size accompanied susceptibility to C. chinensis. Based on linked markers the QTL on these two linkage groups appear to be the same as previously reported in other Asian Vigna. However, several other QTLs were newly detected including one on LG4 that appears unrelated to seed size. Transfer of these new sources of bruchid resistance from V. nepalensis to azuki bean will be aided by the progress being made in azuki genome mapping.     

Dispersal and parasitizing abilities of Eupelmus vuilleti (Hymenoptera: Eupelmidae) within a column of cowpea seeds

Eupelmus vuilleti (Crawford) is an ectoparasitoid of the seed-eating beetle Bruchidius atrolineatus (Pic), which is an important pest of stored cowpea, Vigna unguiculata Walp, seeds in West Africa. Herein, we investigated the dispersal abilities of females within columns of seeds to assess the potential of E. vuilleti as a biological control agent of bruchids in cowpea granaries. The influence of host presence together with the 2 abiotic factors light and gravity on parasitoid movement and parasitization efficiency were analyzed. E. vuilleti females were able to travel through large seed masses and parasitize hosts located at the end of the seed column opposed to their introduction zone. Parasitoid movement was stimulated by light. E. vuilleti females exhibited a negative geotropism. Females introduced at the bottom of the seed column dispersed more and parasitized more hosts than females introduced at the top. Host presence had some influence on the dispersal of the parasitoids within the seed column at a host density of 10 infested seeds for 16,000-18,000 uninfested seeds. This depended on female introduction zone because gravity was the major factor influencing dispersal. The possible applications of these results for biological control of bruchids in cowpea granaries are discussed.