Roger W. Fuester

Occurrence of Emerald Ash Borer (Coleoptera: Buprestidae) and Biotic Factors Affecting Its Immature Stages in the Russian Far East

ABSTRACT Field surveys were conducted from 2008 to 2011 in the Khabarovsk and Vladivostok regions of Russia to investigate the occurrence of emerald ash borer, Agrilus planipennis Fairmaire, and mortality factors affecting its immature stages. We found emerald ash borer infesting both introduced North American green ash (Fraxinus pennsylvanica Marshall) and native oriental ashes (F. mandshurica Rupr. and F. rhynchophylla Hance) in both regions. Emerald ash borer densities (larvae/m2 of phloem area) were markedly higher on green ash (11.3–76.7 in the Khabarovsk area and 77–245 in the Vladivostok area) than on artificially stressed Manchurian ash (2.2) or Oriental ash (10–59). Mortality of emerald ash borer larvae caused by different biotic factors (woodpecker predation, host plant resistance and/or undetermined diseases, and parasitism) varied with date, site, and ash species. In general, predation of emerald ash borer larvae by woodpeckers was low. While low rates (3–27%) of emerald ash borer larval mortality were caused by undetermined biotic factors on green ash between 2009 and 2011, higher rates (26–95%) of emerald ash borer larval mortality were caused by putative plant resistance in Oriental ash species in both regions. Little (<1%) parasitism of emerald ash borer larvae was observed in Khabarovsk; however, three hymenopteran parasitoids (Spathius sp., Atanycolus nigriventris Vojnovskaja-Krieger, and Tetrastichus planipennisi Yang) were observed attacking third - fourth instars of emerald ash borer in the Vladivostok area, parasitizing 0–8.3% of emerald ash borer larvae infesting Oriental ash trees and 7.3–62.7% of those on green ash trees (primarily by Spathius sp.) in two of the three study sites. Relevance of these findings to the classical biological control of emerald ash borer in newly invaded regions is discussed.

Parasitoids Attacking the Emerald Ash Borer (Coleoptera: Buprestidae) in Western Pennsylvania

ABSTRACT Field surveys of the emerald ash borer (EAB), Agrilus planipennis Fairmaire, and associated parasitoids were conducted in Cranberry Township, PA from 11 Mar to 23 Oct 2008. Several species of parasitic Hymenoptera were collected from EAB-infested green ash trees or reared from late-instar EAB larvae, prepupae, and/or pupae. These included Balcha indica (Mani & Kaul), Eupelmus pini Taylor (Eupelmidae), Dolichomitus vitticrus Townes (Ichneumonidae), and 2 additional unidentified ichneumonids, Orthizema sp. Townes and Cubocephalus sp. Townes. Together, these parasitoids caused about 3.6% parasitism of EAB in the field. The most abundant species was B. indica accounting for 82% of all parasitoids recovered during our survey. Subsequent laboratory assays confirmed that B. indica and E. pini are solitary ectoparasitoids of EAB larvae, prepupae, and/or pupae. In addition, both B. indica and E. pini reproduce through thelytokous parthenogenesis; i.e., virgin females produce daughters. These parasitoids may be complementary to current classical biological control programs against EAB in North America, which have been focusing primarily on the introduction of exotic larval and egg parasitoids from China.

Structure and evolution of a proviral locus of Glyptapanteles indiensis bracovirus

BackgroundBracoviruses (BVs), a group of double-stranded DNA viruses with segmented genomes, are mutualistic endosymbionts of parasitoid wasps. Virus particles are replication deficient and are produced only by female wasps from proviral sequences integrated into the wasp genome. Virus particles are injected along with eggs into caterpillar hosts, where viral gene expression facilitates parasitoid survival and therefore perpetuation of proviral DNA. Here we describe a 223 kbp region of Glyptapanteles indiensis genomic DNA which contains a part of the G. indiensis bracovirus (GiBV) proviral genome.ResultsEighteen of ~24 GiBV viral segment sequences are encoded by 7 non-overlapping sets of BAC clones, revealing that some proviral segment sequences are separated by long stretches of intervening DNA. Two overlapping BACs, which contain a locus of 8 tandemly arrayed proviral segments flanked on either side by ~35 kbp of non-packaged DNA, were sequenced and annotated. Structural and compositional analyses of this cluster revealed it exhibits a G+C and nucleotide composition distinct from the flanking DNA. By analyzing sequence polymorphisms in the 8 GiBV viral segment sequences, we found evidence for widespread selection acting on both protein-coding and non-coding DNA. Comparative analysis of viral and proviral segment sequences revealed a sequence motif involved in the excision of proviral genome segments which is highly conserved in two other bracoviruses.ConclusionContrary to current concepts of bracovirus proviral genome organization our results demonstrate that some but not all GiBV proviral segment sequences exist in a tandem array. Unexpectedly, non-coding DNA in the 8 proviral genome segments which typically occupies ~70% of BV viral genomes is under selection pressure suggesting it serves some function(s). We hypothesize that selection acting on GiBV proviral sequences maintains the genetic island-like nature of the cluster of proviral genome segments described herein. In contrast to large differences in the predicted gene composition of BV genomes, sequences that appear to mediate processes of viral segment formation, such as proviral segment excision and circularization, appear to be highly conserved, supporting the hypothesis of a single origin for BVs.

Parasitoid Guilds of Agrilus Woodborers (Coleoptera: Buprestidae): Their Diversity and Potential for Use in Biological Control

Literature studies in North America (US and Canada), Europe, and Asia (particularly Russia, China, Japan, and the Korean peninsula) were reviewed to identify parasitoid guilds associated with Agrilus woodborers. There are at least 12 species of hymenopteran parasitoids attacking eggs of Agrilus beetles and 56 species (36 genera), attacking Agrilus larvae infesting various host plants in North America, Asia, and Europe. While most of the egg parasitoids (9 species) belong to the family Encyrtidae, a majority of the larval parasitoids are members of five families: Braconidae (24 species/11 genera), Eulophidae (8 species/4 genera), Ichneumonidae (10 species/9 genera), and Eupelmidae (6 species/5 genera). The highest rate of Agrilus egg parasitism (>50%) was exerted by encyrtid wasps (4 species) in North America, Asia, and Europe. In contrast, the highest rate of Agrilus larval parasitism (>50%) was caused by species in two genera of braconids: Atanycolus (North America) and Spathius (Asia), and one eulophid genus, Tetrastichus (Asia and Europe). Reported rate of Agrilus larval parasitism ichneumonids was frequent in North America, but generally low (<1%). Potential for success in biological control of emerald ash borer (Agrilus planipennis Fairmaire) in the USA with North American native parasitoids and old-association Asian parasitoids is discussed.

Host Range of Aphantorhaphopsis samarensis (Diptera: Tachinidae), a Larval Parasite of the Gypsy Moth (Lepidoptera: Lymantriidae)

Abstract Aphantorhaphopsis samarensis (Villeneuve), a European tachinid, has been released in North America for classical biological control of the gypsy moth, Lymantria dispar (L.). This study examined the host range of A. samarensis. We used three approaches: (1) field collection and rearing of potential alternate or alternative hosts at European sites where A. samarensis was known to occur, (2) choice tests offering females of A. samarensis both gypsy moth and native North American species of Lepidoptera, and (3) host suitability tests in which we artificially inoculated European nontarget species with mature eggs of A. samarensis dissected from gravid females. In the field studies, we collected a total of 851 caterpillars, belonging to at least 54 species other than gypsy moth in 11 families, over several years, but none yielded A. samarensis, with the possible exception of a single larva of Lymantria monacha (L.) and the rusty tussock moth, Orgyia antiqua (L.), which yielded puparia resembling those of A. samarensis. In laboratory tests, we offered females of A. samarensis 11 native species of North American Lepidoptera in five families, but only the lymantriid Orgyia leucostigma (J. E. Smith), was successfully parasitized. In host suitability studies, we inoculated 10 species of Lepidoptera in eight families with mature eggs of A. samarensis, but parasitism was successful only in L. dispar. We conclude that A. samarensis has a high degree of host specificity.

Incidence and ecological relationships of parasitism in larval populations of Lymantria dispar (Lepidoptera: Lymantriidae)

Abstract Larval parasitism of gypsy moth, Lymantria dispar (L.), was monitored in 11 study plots in northern New Jersey from 1978 to 1988. Five parasitoid species were commonly found. Parasitism by Cotesia melanoscelus (Ratzeburg) was highest at the peak of egg mass density during a gypsy moth outbreak. Phobocampe unicincta (Gravenhorst) had low and relatively constant parasitism levels through the outbreak, but parasitism fell near zero after the host population crashed. Parasitism by Compsilura concinnata Meigen peaked during the decline of gypsy moth populations and probably was related primarily to the presence of alternate hosts. Parasetigena silvestris (Robineau-Desvoidy) had the highest levels of parasitism overall. Levels remained high throughout the outbreak and declined with the host populations. Parasitism by Blepharipa pratensis (Meigen) was highest in the first year of the study, when egg mass density was increasing, and declined steadily thereafter, following the trend of host larval density. Parasitism by all species except C. concinnata was correlated significantly and positively with the density of host larvae. Three species showed delayed density dependence. Direct density dependence, density independence, or indeterminate density relationships were observed for all species across study plots within seasons. The relationship of parasitism to ecological factors was investigated through stepwise multiple regression analysis. Parasitism by C. melanoscelus was correlated primarily with winter and spring temperatures and gypsy moth egg mass density. For P. unicincta parasitism, most variation was explained by parasitism by C. melanoscelus and stand density. Parasitism by C. concinnata was correlated most strongly with stand composition and percentage infection by gypsy moth nuclear polyhedrosis virus. Percentage defoliation of oaks explained most variation in parasitism by P. silvestris and B. pratensis .

Hymenopteran Parasitoids Attacking the Invasive Emerald Ash Borer (Coleoptera: Buprestidae) in Western and Central Pennsylvania

ABSTRACT We conducted field surveys of the emerald ash borer (EAB), Agrilus planipennis Fairmaire, and associated larval parasitoids in western and central Pennsylvania (Cranberry Township in Butler County and Granville in Mifflin County) in the spring and fall of 2009. The survey procedure involved destructively debarking sections of the main trunk (bole) of EAB-infested green ash (Fraxinus pennsylvanica Marsh.) trees from the ground to the height of 2 m. Three species of the hymenopteran parasitoids were consistently recovered from EAB larvae observed in both survey sites, including two indigenous species of braconids, Spathius laflammei Provancher (= Spathius benefactor Matthews) and Atanycolus nigropyga Shenefelt and the exotic (accidentally introduced) eupelmid Balcha indica (Mani & Kaul). In addition, there are three unidentified species of hymenopteran parasitoids including two braconids Atanycolus sp. [possibly Atanycolus disputabilis (Cresson)] and Spathius sp. (at the Butler Co. site) and one ichneumonid Dolichomitus sp. (at the Mifflin Co. site). These parasitoids together parasitized 0.5–4.6% and 0.5–1.5% of the sampled EAB hosts at the Butler and Mifflin Co. sites, respectively. Parasitism rate by each species or group of those hymenopteran parasitoids varied between the two survey sites—with parasitism rates being generally higher at the Butler Co. site than at the Mifflin Co. site. Studies are needed to determine if those new associations of North American indigenous braconid parasitoids with EAB may play a complementary role in controlling this invasive pest.

Male-Biased Sex Ratios in Glyptapanteles flavicoxis (Hymenoptera: Braconidae), a Parasitoid of the Gypsy Moth (Lepidoptera: Lymantriidae)

Abstract Male-biased sex ratios in populations of parasitic wasps used in biological control are undesirable, because a low proportion of females can prevent the establishment of introduced species or hinder commercial production of species used for augmentative control. Studies were conducted on potential factors contributing to male-biased sex ratios that have been encountered in laboratory rearings of the braconid endoparasitoid Glyptapanteles flavicoxis (Marsh) using the gypsy moth, Lymantria dispar (L.), as a host. Sex determination in this wasp is arrhenotokous (haplodiploid). In the first experiment, we stored adults at 13 or 16°C and allowed them to mate at 20 or 25°C and found that sex ratios (expressed as percentage females) did not differ among progeny of parents; many females produced all male progeny, suggesting that they had not been fertilized. In the second experiment, females were exposed to hosts soon (0–60 min) after mating or 23–25 h later. Sex ratios were higher (less male-biased) in progenies of females provided with the rest period than in those which were not. In a third experiment, females were allowed to mate from one to four times with a given male. Although differences between these groupings were not statistically significant, the data suggested that more than two matings might depress sex ratios of progeny. An alternative analysis with only two groupings (1–2 matings and 3–4 matings) suggested that more than two matings might increase male bias of progeny. Therefore, we suggest that matings of this species be monitored in sleeve cages so that paired females can be removed and separated after copulation to diminish the likelihood of excessive matings, then given a rest period before they are offered hosts for parasitization.

Deletion of v-chiA from a Baculovirus Reduces Horizontal Transmission in the Field

ABSTRACT Nucleopolyhedroviruses (NPVs) can initiate devastating disease outbreaks in populations of defoliating Lepidoptera, a fact that has been exploited for the purposes of biological control of some pest insects. A key part of the horizontal transmission process of NPVs is the degradation of the larval integument by virus-coded proteins called chitinases, such as V-CHIA produced by the v-chiA genes. We used recombinant and naturally occurring strains of the Lymantria dispar NPV (LdMNPV) to test horizontal transmission in the field, release of virus from dead larvae under laboratory conditions, and cell lysis and virus release in cell culture. In the field, strains of LdMNPV lacking functional v-chiA genes showed reduced horizontal transmission compared to wild-type or repaired strains. These findings were mirrored by a marked reduction in released virus in laboratory tests and cell culture when the same strains were used to infect larvae or cells. Thus, this study tests the pivotal role of liquefaction and the v-chiA gene in field transmission for the first time and uses complementary laboratory data to provide a likely explanation for our findings.

Interactions between an injected polydnavirus and per os baculovirus in gypsy moth larvae

Larval gypsy moths, Lymantria dispar (Lepidoptera:Lymantriidae) were co-infected with the L. dispar nucleopolyhedrovirus (LdMNPV) and the Cotesia melanoscela (Hymenoptera:Braconidae) polydnavirus (CmeBV). CmeBV was given along with a parasitoid egg and calyx products in a stinging event, or in the form of an injection of calyx-derived extract. LdMNPV was delivered per os, integrated into artificial diet. Mortality from all sources was recorded over the subsequent three-week period. Neither parasitism nor injections of purified CmeBV with toxin had any effect on the amount of mortality caused by concurrent challenges with LdMNPV.