Matthew H. Greenstone

Tracking the role of alternative prey in soybean aphid predation by Orius insidiosus: a molecular approach

The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is a pest of soybeans in Asia, and in recent years has caused extensive damage to soybeans in North America. Within these agroecosystems, generalist predators form an important component of the assemblage of natural enemies, and can exert significant pressure on prey populations. These food webs are complex and molecular gut‐content analyses offer nondisruptive approaches for examining trophic linkages in the field. We describe the development of a molecular detection system to examine the feeding behaviour of Orius insidiosus (Hemiptera: Anthocoridae) upon soybean aphids, an alternative prey item, Neohydatothrips variabilis (Thysanoptera: Thripidae), and an intraguild prey species, Harmonia axyridis (Coleoptera: Coccinellidae). Specific primer pairs were designed to target prey and were used to examine key trophic connections within this soybean food web. In total, 32% of O. insidiosus were found to have preyed upon A. glycines, but disproportionately high consumption occurred early in the season, when aphid densities were low. The intensity of early season predation indicates that O. insidiosus are important biological control agents of A. glycines, although data suggest that N. variabilis constitute a significant proportion of the diet of these generalist predators. No Orius were found to contain DNA of H. axyridis, suggesting intraguild predation upon these important late‐season predators during 2005 was low. In their entirety, these results implicate O. insidiosus as a valuable natural enemy of A. glycines in this soybean agroecosystem.

Barcoding generalist predators by polymerase chain reaction: carabids and spiders

Identification of arthropod predators is challenging when closely related species are found at a given locality. Identification of the immature stages is especially problematic, because distinguishing morphological features are difficult to use or have not been described. We used polymerase chain reaction (PCR) to distinguish closely related carabids and spiders, and to match eggs and larvae (or nymphs) with identified adult parents. Within the Carabidae, we amplified species‐specific mitochondrial cytochrome oxidase I (COI) fragments for three species each in the genera Poecilus and Harpalus, and two each in Chlaenius and Bembidion. Within the Araneae, we amplified species‐specific COI fragments for two Hibana species (Anyphaenidae), Pardosa milvina and Rabidosa rabida (Lycosidae), Frontinella communis and Grammonota texana (Linyphiidae), and Cheiracanthium inclusum (Miturgidae). We are able to correctly identify all immature stages tested — eggs, larvae (or nymphs) and pupae — by comparison of the amplified fragments with those of the adults. Using COI markers as species identifiers is a tenet of the Barcode of Life initiative, an international consortium to provide a molecular identifier for every animal species.

Differential impact of adults and nymphs of a generalist predator on an exotic invasive pest demonstrated by molecular gut-content analysis

Generalist predators have the capacity to regulate herbivore populations through a variety of mechanisms, but food webs are complex and defining the strength of trophic linkages can be difficult. Molecular gut-content analysis has revolutionized our understanding of these systems. Utilizing this technology, we examined the structure of a soybean food web, identified the potential for adult and immature Orius insidiosus (Hemiptera: Anthocoridae) to suppress Aphis glycines (Hemiptera: Aphididae), and tested the hypotheses that foraging behaviour would vary between life stages, but that both adults and immatures would exert significant predation pressure upon this invasive pest. We also identified the strength of trophic pathways with two additional food items: an alternative prey item, Neohydatothrips variabilis (Thysanoptera: Thripidae), and an intraguild predator, Harmonia axyridis (Coleoptera: Coccinellidae). A. glycines constituted a greater proportion of the diet of immature O. insidiosus, but N. variabilis DNA was found in greater frequency in adults. However, both life stages were important early-season predators of this invasive pest, a phenomenon predicted as having the greatest impact on herbivore population dynamics and establishment success. No adult O. insidiosus screened positive for H. axyridis DNA, but a low proportion (2.5%) of immature individuals contained DNA of this intraguild predator, thus indicating the existence of this trophic pathway, albeit a relatively minor one in the context of biological control. Interestingly, approximately two-thirds of predators contained no detectable prey and fewer than 3% contained more than one prey item, suggesting the possibility for food limitation in the field. This research implicates O. insidiosus as a valuable natural enemy for the suppression of early-season A. glycines populations.

Determination of prey antigen half-life in Polistes metricus using a monoclonal antibody-based immunodot assay

In order to derive quantitative estimates of predation rate from serological gut analysis data, one must have an estimate of the interval during which a meal can be detected after feeding. In practice this has turned out to be ‘Dmax,’ defined as ‘…the time from finishing a meal until that meal could just no longer be detected in any individuals.’ However Dmax substitutes an absolute limit for what is really a continuous variable with significant variation. We examined this problem in a study of the detectability of Helicoverpa zea Boddie (Lepidoptera: Noctuidae) fifth instar remains in the guts of Polistes metricus Say (Hymenoptera: Vespidae). Wasps were maintained on Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) fifth instars before being fed a single H. zea fifth instar. They were killed and frozen at 0, 24, 48 and 96 h intervals, with those held for more than 24 h fed a single T. ni fifth instar at 24 h intervals in order to simulate continued feeding. Wasp abdomens were assayed by immunodot, using a monoclonal antibody to H. zea arylphorin. There was a logarithmic decay in the proportion of P. metricus positive over time, a single H. zea fifth instar meal having a detectability half‐life of 19.4 h at field temperatures. If prey antigen detectability decays exponentially, then a detectability half‐life is a more appropriate unit of detectability than an absolute detectability period.

The detectability half‐life in arthropod predator–prey research: what it is, why we need it, how to measure it, and how to use it

Molecular gut‐content analysis enables detection of arthropod predation with minimal disruption of ecosystem processes. Most assays produce only qualitative results, with each predator testing either positive or negative for target prey remains. Nevertheless, they have yielded important insights into community processes. For example, they have confirmed the long‐hypothesized role of generalist predators in retarding early‐season build‐up of pest populations prior to the arrival of more specialized predators and parasitoids and documented the ubiquity of secondary and intraguild predation. However, raw qualitative gut‐content data cannot be used to assess the relative impact of different predator taxa on prey population dynamics: they must first be weighted by the relative detectability periods for molecular prey remains for each predator–prey combination. If this is not carried out, interpretations of predator impact will be biased towards those with the longest detectabilities. We review the challenges in determining detectability half‐lives, including unstated assumptions that have often been ignored in the performance of feeding trials. We also show how detectability half‐lives can be used to properly weight assay data to rank predators by their importance in prey population suppression, and how sets of half‐lives can be used to test hypotheses concerning predator ecology and physiology. We use data from 32 publications, comprising 97 half‐lives, to generate and test hypotheses on taxonomic differences in detectability half‐lives and discuss the possible role of the detectability half‐life in interpreting qPCR and next‐generation sequencing data.

SPIDER PREDATION: SPECIES-SPECIFIC IDENTIFICATION OF GUT CONTENTS BY POLYMERASE CHAIN REACTION

Abstract We extend detection of arthropod predator gut contents by polymerase chain reaction (PCR), heretofore restricted to insect predators, to spiders. Single individuals of the corn lead aphid, Rhopalosiphum maidis, were detected in the guts of spiderlings of Oxyopes salticus up to 12 h after feeding; individuals of the congeneric bird cherry oat aphid, R. padi, were not detected. Unfed O. salticus and Misumenops sp. were also negative.

Molecular Evidence for a Species Complex in the Genus Aphelinus (Hymenoptera: Aphelinidae), with Additional Data on Aphidiine Phylogeny (Hymenoptera: Braconidae)

Abstract Mitochondrial 16s rDNA was sequenced from nine different populations of Aphelinidae and 10 of aphidiinae. Sequence divergences between populations within a species are low, ranging from 0 to 0.38%. Divergences among species within the same genus range from 0 to 8.71%. Aphelinus asychis Walker has a sequence divergence from the other Aphelinus spp. of 8.71%, which is even higher than the divergences among the aphidiine genera Lysiphlebus, Aphidius and Diaeretiella. Our 16s rDNA phylogeny for aphidiines is concordant with a previously published NADH1 dehydrogenase phylogeny. Our analysis identifies a complex comprising A. albipodus (Hayat & Fatima), A. varipes (Foerster), and A. hordei (Kurdjumov). The sequence divergences within this complex are low, ranging from 0 to 0.38% with an average of 0.19%, which suggests that the three species within the A. varipes complex diverged within the last ≈90,000 yr.

Specific ribosomal DNA marker for early polymerase chain reaction detection of Aphelinus hordei (Hymenoptera: Aphelinidae) and Aphidius colemani (Hymenoptera: Aphidiidae) from Diuraphis noxia (Homoptera: Aphididae).

Abstract To monitor aphid parasitism by Aphelinus hordei (Kurdjumov) and Aphidius colemani Viereck, we developed specific ribosomal DNA markers to distinguish them from several other cereal aphid parasitoid species and two important host species, the Russian wheat aphid, Diuraphis noxia (Mordvilko), and the greenbug, Schizaphis graminum (Rondani). Ribosomal DNA sequences for the internal transcribed spacer 2 (ITS2) were first cloned and sequenced from A. hordei, A. albipodus Hayat & Fatima, A. asychis Walker, A. varipes (Foerster), A. colemani, D. noxia, and S. graminum. We designed specific primers based on the ITS2 sequences. Polymerase chain reaction (PCR) amplification of wasp and aphid DNA using these primers, followed by agarose gel electrophoresis, successfully distinguishes A. hordei and A. colemani from all three other Aphelinus species and two aphid species. A 411-bp nucleotide fragment and a 571-bp fragment were amplified only from A. hordei and from A. colemani, respectively, and no such fragments were amplified from any other wasp species or aphids. DNA could be detected at a level as low as 10−3 adult wasp equivalent for A. hordei and 5 × 10−4 adult wasp equivalent for A. colemani. The DNA of both species was detectable in parasitized D. noxia 24 h after initial contact with adult parasitoid pairs.

Prey preference and host suitability of the predatory and parasitoid carabid beetle, Lebia grandis, for several species of Leptinotarsa beetles.

Abstract Lebia grandis (Coleoptera: Carabidae), recorded as a parasitoid only on Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae), is capable of parasitizing the false potato beetle, L. juncta, and also L. haldemani. Historical records show that L. decemlineata, while the only recorded host, was not present in much of the original range of L. grandis, and may not have been its host prior to its expansion into eastern North America, where L. juncta is endemic. Our laboratory comparisons suggest that L. juncta, the presumptive original host, best supports the development of the parasitoid larval L. grandis, based on 43.6% successful emergence of the adult carabid parasitoid, compared to 11.5% from the two other Leptinotarsa species. L. grandis adults accept eggs and larvae of all 3 Leptinotarsa species as adult food. Naive, newly-emerged adults show no preference when presented the 3 species of third-instar larvae, which they consume at a mean rate of 3.3 per day, a rate which does not differ significantly by sex, larval host, or weight at emergence. When presented with equal amounts by weight of the 3 species of Leptinotarsa eggs, such adults consume the equivalent of 23.0 L. decemlineata eggs per day, with consumption of L. juncta eggs 67% higher by weight than L. decemlineata consumption. Insight into the biotic and abiotic limitations on L. grandis should aid in determining its potential for suppression of Colorado potato beetle by biological control in diverse agroecosystems.

Predation of Stink Bugs (Hemiptera: Pentatomidae) by a Complex of Predators in Cotton and Adjoining Soybean Habitats in Georgia, USA

Abstract Stink bugs (Hemiptera: Pentatomidae) are economic pests of cotton and soybean. This study was conducted to examine predation on stink bugs by arthropod predators in cotton and adjoining soybean habitats. Gut-content analysis based on polymerase chain reaction (PCR) was used to detect stink bug deoxyribonucleic acid (DNA) in predators collected from both crops over a 5 wk period. Nezara viridula (L.), Euschistus servus (Say), Chinavia hilaris (Say), and Euschistus quadrator Rolston were detected on soybean and cotton. Piezodorus guildinii (Westwood) and Thyanta custator custator (F.) were detected only on soybean whereas Euschistus tristigmus (Say) was detected only on cotton. Over both crops, 13 predators screened positive for a variety of stink bug species DNA by PCR analysis: Geocoris punctipes (Say) and Geocoris uliginosus (Say) (Hemiptera: Geocoridae), Orius insidiosus (Say) (Hemiptera: Anthocoridae), Hippodamia convergens Guérin-Méneville, Harmonia axyridis (Pallas) (cotton), and Scymnus sp. (cotton) (Coleoptera: Coccinellidae), Oxyopes salticus Hentz and Peucetia viridans (Hentz) (cotton) (Araneae: Oxyopidae), Solenopsis invicta Buren (Hymenoptera: Formicidae), Podisus maculiventris (Say) (Hemiptera: Pentatomidae), Mecaphesa asperata (Hentz) (Araneae: Thomisidae), Zelus renardii Kolenati (Hemiptera: Reduviidae), and Notoxus monodon (F.) (cotton) (Coleoptera: Anthicidae). In soybean, the percentage of G. punctipes and G. uliginosus screening positive for N. viridula was high, 87.3%, whereas the percentage screening positive for E. servus was moderately high, 60.3%. In cotton, the percentage of N. viridula DNA in gut-contents of O. insidiosus was high, 91.6%. Detection of P. guildinii and/or T. c. custator DNA in predators in cotton and of E. tristigmus DNA in predators in soybean demonstrated predator dispersal between soybean and cotton. In soybean, the percentage of P. guildinii DNA in gut contents of G. punctipes, G. uliginosus, and O. insidiosus, including those individuals in cotton that dispersed from soybean, was high. We conclude that a complex of arthropod predators prey on a complex of stink bugs in both cotton and adjoining soybean while foraging in and between these crops.