Laboratory and Field Observations of the Behavior of <Emphasis Type="Italic">Eustenopus villosus</Emphasis> while Feeding and Ovipositing on Yellow Starthistle

The feeding and oviposition behavior of postdiapausal Eustenopus villosus (Boheman) on young and late stage buds, respectively of yellow starthistle, Centaurea solstitialis L., was documented in the laboratory and field. Postdiapausal adult feeding on young buds took over an hour to complete in most cases and was conducted by both sexes. Feeding bouts generally occurred in the sequence of explore, feeding, and budwalk. Oviposition included a feeding phase to prepare an oviposition cavity within the bud; thus, oviposition bouts included some of the same behavioral elements as postdiapausal feeding. The standard sequence of behavioral elements involved with oviposition included exploring, feeding, turning, ovipositing, and budwalking. The feeding element during the oviposition bout often lasted 2 h and was similar in the field and in the lab. Postdiapausal adult feeding on young capitula and stems, and larval feeding on developing ovaries and achenes, makes this weevil especially destructive on a per insect basis.     

Biology of Larinus curtus Hochhut (Coleoptera: Curculionidae), a European Weevil for Biological Control of Yellow Starthistle Centaurea solstitialis L (Asteraceae), in the United States

The biology of the weevil Larinus curtus Hochhut was studied in the field in northern Greece and in the laboratory in Rome, Italy, and in Thermi, near Thessaloniki, Greece. The species is univoltine, and adults overwinter in ground litter. Eggs are inserted into the flowers of yellow starthistle (Centaurea solstitialis L.) where the larvae feed mainly on developing achenes, destroying on average over 96% of the seeds in infested flowerheads. Overwintered adults lived up to 84 days, females laid up to 70 eggs each, eggs hatched 4.2 ± 0.6 days after being laid, larvae required 17 to 20 days to develop through the four instars, and pupal development required 4 to 5 days under laboratory conditions. Six percent of 360 seedheads collected on July 13 and 28, 1988 were infested with L. curtus larvae and up to 89% of the larvae were parasitized. The species is recommended for the biological control of C. solstitialis in the United States.     

A Histological Study of the Effect of Feeding bySmicronyxspp. (Coleoptera: Curculionidae) Larvae on Seed Production byStriga hermonthica(Scrophulariaceae)

Experiments were conducted in Burkina Faso to determine the effect of feeding bySmicronyxspp. (Coleoptera: Curculionidae) larvae on the development of fruit capsule and seed production inStriga hermonthica(Scrophulariaceae). In treated plotsSmicronyxadults were released in the cages while in untreated plots (= control) noSmicronyxwere released. TheStrigacapsules were collected, fixed, and prepared for histological examination. UninfestedStrigacapsules developed normally. In infested capsules, three types of galls were distinguished: they reflected the development of capsule and the seeds. There was a synchrony between seed development and larval development in the same capsule. In most instances, one egg or larva was found per gall.Smicronyxlarvae completely destroyedStrigaseeds in the developing capsule by two mechanisms: (1) by directly eating most of the seeds and (2) by eating the placenta that normally feed the seeds.     

Successful oviposition and reproductive biology of Aprostocetus vaquitarum (Hymenoptera: Eulophidae): A predator of Diaprepes abbreviatus (Coleoptera: Curculionidae)

Aprostocetus vaquitarum (Wolcott) causes 78–91 percent mortality to eggs of Diaprepes abbreviatus (L.), under field conditions in southern Florida. In the laboratory, A. vaquitarum was reared on D. abbreviatus eggs at 25 °C, a photoperiod of 12:12 (L:D) and with abundant hosts, A. vaquitarum adult females lived around 15 days. Oviposition was significantly affected by the age of the host egg mass. Egg masses aged 0- to 3-day-old were accepted significantly better than those aged 4–6 days. The mean number of eggs deposited per female was around 53, with extreme values of 124 and 19 eggs per female. Using these data in combination with the sex ratio observed in the field (0.16) and the duration of the preimaginal stages, r_m (0.168–0142 day⁻¹), T (22.39–22.89 days), and R₀ (43.03–25.81 females per female) were calculated.     

Biology of Heilipodus ventralis (Coleoptera: Curculionidae), an Argentine Weevil for Biological Control of Snakeweeds (Gutierrezia spp.) in the United States

The Argentine root-boring weevil Heilipodus ventralis (Hustache) is a candidate for biological control of the perennial snakeweeds Gutierrezia sarothrae (Pursh) Britton and Rusby and G. microcephala (DeCandolle) A. Gray, poisonous native weeds of rangelands of the southwestern United States. In Argentina, the weevil occurs in semiarid regions from Tucumán south to Chubut, which are climatically similar to broad areas of the southwestern United States. Laboratory-reared females lived ca. 112 days and laid ca. 117 eggs. The eggs hatched in ca. 15 days. The larvae had eight instars; they required ca. 151 days and pupae ca. 27 days to develop. Adult weevils emerged from the taproots in early summer, fed on the leaves and terminals, and oviposited mostly in the crown near the soil line. The feeding of one or more pairs of caged adults killed medium-sized plants. The larvae tunneled downward to the taproot where they pupated. They overwintered in the taproots of these perennial host plants and pupated in the spring. A generation required 1 year but some individuals probably required two growing seasons. At Peninsula Valdés, Chubut, H. ventralis preferred Gutierrezia solbrigii Cabrera to Grindelia chiloensis (Corn.) Cabrera by a ratio of 1.9 to 1.0. In the field there, crowns of large Gu. solbrigii (average 60 cm canopy diameter) contained an average 5.0 larvae per plant, those of small plants (23 cm diameter) contained 1.1 larvae, and plants smaller than 10 cm rarely contained larvae. No insect parasitoids or predators were found attacking any stage. H. ventralis probably evolved on xerophytic, temperate Astereae, from ancestors of the genus Heilipus that fed on species of ancient, hygrophytic, tropical plant families.     

Host Specificity of the Argentine Root-Boring Weevil, Heilipodus ventralis (Coleoptera: Curculionidae), a Potential Biocontrol Agent for Snakeweeds (Gutierrezia: Asteraceae) in Western North American Rangelands—U.S. Quarantine Tests

Native snakeweeds, especially Gutierrezia sarothrae (Pursh) Britton and Rusby and Gutierrezia microcephala (DC.) A. Gray, are among the most widespread and damaging weeds of rangelands in the western United States and northern Mexico. The genus long ago spread to southern South America, where further speciation occurred. We have found several species of insects in Argentina that damage other species of snakeweeds there and are possible candidates for biological control in North America. The first of these, the root-boring weevil, Heilipodus ventralis (Hustache), was tested in Argentina and then sent to the USDA-ARS Insect Quarantine Facility at Temple, Texas, for host specificity testing on North American plants. We tested H. ventralis on 40 species of the family Asteraceae, in 19 tests of five types, using 686 adults and 365 larvae. Host specificity increased from adult feeding, to ovipositional selection, to larval development. At Temple, adults fed mostly on 6 species of the closely related genera Grindelia, Gutierrezia, and Gymnosperma, but with substantial feeding on four other genera of the two preferred subtribes Solidagininae and Machaerantherinae and on Baccharis in the tribe Baccharidinae, with lesser feeding on the subtribe Asterinae, all in the tribe Astereae, and on 1 species in the tribe Anthemideae. Females oviposited primarily on the same 6 species but very little on plants outside the 2 preferred subtribes. Larvae developed only on 9 of the 29 U.S. plant species tested, 6 within the two preferred subtribes and on Brickellia and Aster in other tribes. Only 5 species of three genera appear to be potential true hosts of H. ventralis in North America, on which all stages of the life cycle, adult feeding, oviposition, and larval development, can take place; these are Gymnosperma glutinosum (Spreng.) Less., Gutierrezia grandis Blake, Gut. microcephala, Gut. sarothrae, and Grindelia lanceolata Nutt. None of these genera contain species of economic or notable ecological value; the few rare species appear to be protected by habitat isolation from attack by H. ventralis. H. ventralis, therefore, appears sufficiently host specific for field release in North America. This is the first introduced biocontrol agent to be approved for release in a continental area to control a native weed.     

Distribution of Insect Attacks in Biological Control of Weeds: Infestation of Centaurea virgata Flowerheads by a Gall Fly

The success of biological control efforts to reduce weed density through release of insects may depend as much on the distribution of insect attacks among individual plants or plant parts as on the mean level of infestation. We used an index of dispersion to describe the distribution of Urophora quadrifasciata (Diptera: Tephritidae) galls among squarrose knapweed (Centaurea virgata) flowerheads at 18 west central Utah sites in the first 5 years following introduction of the biological control agent. Two thirds of the samples showed a significantly aggregated distribution of galls among flowerheads. Statistical analysis showed that site and year accounted for relatively small proportions of the variance in the index of dispersion. The degree of gall aggregation among flowerheads was positively correlated with the mean flowerhead quality (mean number of seeds per flowerhead; P = 0.013) and tended to be negatively correlated with the mean fly density per flowerhead at a site in a given year (P = 0.097). Our data suggest that higher quality flowerheads, and possibly higher quality plants, are preferentially attacked by U. quadrifasciata and therefore are more heavily subject to reduced reproductive potential through biological control. However, an aggregated distribution of fly attacks may undercut the potential of the fly to reduce seed production by the weed population as a whole. Understanding both the distribution of insect attacks among individual plants and the behavioral mechanisms producing such distribution patterns is important to the biological control of weeds.     

The Effect of Variability in the Phenology of the Reproductive Stages of Scotch Broom (Cytisus scoparius) on the Synchronization of the Life Stages of Broom Seed Beetle (Bruchidius villosus) in New Zealand

Variability in timing of the reproductive stages of Scotch broom (Cytisus scoparius) may influence synchronization and establishment of the broom seed beetle (Bruchidius villosus), a biological control agent. A sampling scheme was devised to compare the phenologies of Scotch broom at different sites in the same season and in different seasons at the same site. The synchrony of the broom seed beetle's life stages with those of the host plant was also determined. The phenology of Scotch broom varied only slightly from season to season at Lincoln, but could vary considerably between sites in the same season. At both sites where it is established, the broom seed beetle was synchronized with its host; adult beetles were present throughout the flowering period. Eggs were found on suitable green pods. The broom seed beetle appears capable of adapting to the phenology of its host and has the potential to be an effective agent for Scotch broom. Variability in phenology of the reproductive stages of Scotch broom, even at nearby sites, must be taken into account by practitioners of biological control when releasing broom seed beetles and later when sampling beetles to determine establishment.     

Assessment of risk of attack to safflower by Ceratapion basicorne (Coleoptera: Apionidae), a prospective biological control agent of Centaurea solstitialis (Asteraceae)

Ceratapion basicorne (Coleoptera: Apionidae) is a prospective biological control agent of yellow starthistle (Centaurea solstitialis, Asteraceae: Cardueae), which is an important invasive alien weed in the western United States. Previous studies have shown that it is possible for this insect to oviposit on and complete development on safflower (Carthamus tinctorius) under no-choice laboratory conditions; however, it has never been reported as a pest of safflower. Field experiments were conducted at three sites in eastern Turkey during 3 years to evaluate the risk of attack on safflower by this insect in its native range. At two sites where C. basicorne was the only apionid observed, no safflower plants were attacked despite high attack rates on yellow starthistle test plants (48–98% of plants infested). At a third site, where C. basicorne and three other species in the same genus; C. scalptum, C. orientale, and C. onopordi were present, 8–26% of safflower plants were infested, but none of the insects reared from safflower during 3 years were C. basicorne. Other authors have reported rearing C. basicorne from field-collected plants of only Ce. solstitialis, Ce. cyanus, Ce. depressa, and Cnicus benedictus. Our results indicate that C. basicorne does not attack safflower under field conditions and that its introduction would not pose a risk to this crop.     

Insecticidal effect of Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreaes) in combination with three diatomaceous earth formulations against Sitophilus granarius (L.) (Coleoptera: Curculionidae)

The insecticidal effect of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreaes) in combination with three diatomaceous earth (DE) formulations against adults of the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae) was tested in the laboratory. The three DEs were Insecto™, SilicoSec^® and PyriSec^®. The fungus was applied at 400 ppm alone, or in combination with 200 ppm of each of the three DEs. Mortality was measured after 7 d of exposure. Bioassays were conducted at three temperatures 20, 25 and 30 °C and two relative humidities (rh) 55% and 75%. On wheat treated with B. bassiana alone, mortality was higher at 55% than at 75% rh. Also, the fungus alone was less effective at 20 °C than at the other two temperatures tested, but mortality did not exceed 52% for any of the conditions tested. Similar mortality levels were also noted on wheat treated with each of the three DEs alone. The simultaneous presence of B. bassiana and DE increased weevil mortality. In this combination, mortality was higher at high temperatures and low rh, and this effect was similar for all DEs tested. Progeny production on wheat treated with B. bassiana was higher that the respective progeny counts in the DE-treated wheat. The results indicate that a combination of B. bassiana and DEs is effective against S. granarius, under a broad range of temperature and rh levels in stored wheat.     

Host range of Ceutorhynchus assimilis (Coleoptera: Curculionidae), a candidate for biological control of Lepidium draba (Brassicaceae) in the USA

Ceutorhynchus assimilis has been selected as a potential biological control agent of Lepidium draba, which is a Eurasian invasive weed in North America. Preliminary studies indicated specificity of this weevil collected in southern France on L. draba. This result was in discord with the pest status of C. assimilis found in the literature. Host-specificity tests based both on field and laboratory experiments showed heterogeneity in the host spectrum of the weevils reared from different host-plants as determined by larval development. However, no distinguishable morphological differences could be visually detected between the populations feeding on different host-plants. All sampled populations of weevils were polyphagous as adults. Weevils reared from L. draba were specific to this plant for their complete larval development. Conversely, populations living on other wild and cultivated Brassicaceae species were not able to use L. draba as a host plant. Such differentiation is further highlighted by other biological aspects such as plant infestation rates, sex-ratio, duration of larval development, and differences in the timing of their life cycles. These results demonstrate that C. assimilis, an insect species formerly considered as a pest of Brassicaceae, is characterized by its host-range variability, with one population being potentially useful in the biological control of L. draba. Moreover, this example points to the need to test multiple populations of biological control agents in assessing risk.     

Association and Synchrony ofSmicronyx guineanusVoss,S. umbrinusHustache (Coleoptera: Curculionidae), and the Parasitic WeedStriga hermonthica(Del.) Benth. (Scrophulariaceae)

Field experiments were conducted in 1992 and 1993 at Kaya, Burkina Faso, West Africa, in fields of sorghum (Sorghum bicolor) and pearl millet (Pennisetum americanum).Striga hermonthica(witchweed) was sampled weekly using a square-meter metal frame. Concurrently, adult populations of the weevilsSmicronyx guineanusVoss andS. umbrinusHustache were sampled weekly using a Univac portable suction sampler to assess the synchrony ofSmicronyxwithStriga.χ²tests for independence of the populations ofSmicronyxandStrigaindicated a good synchrony of the active stages of the life cycle of the weevils with the period of occurrence of the witchweed. The Univac portable suction sampler method was also used to determine the degree of association betweenSmicronyxandStriga.There was a positive association between the weevil and the witchweed. The percentage ofStrigaplants bearing galls caused bySmicronyxwas determined on 39 occasions and galls were found in every field visited (n = 50). The mean galling percentage ranged from 1 to 84%. A search for alternate hosts was done by sampling weevil adults on weeds surrounding the farmers' fields. NoSmicronyxadult was caught on these weeds before the emergence of volunteerStrigaplants.     

Suppression of Boll Weevil Infestations (Coleoptera: Curculionidae) Occurring on Fallow-Season Cotton in Southern Texas by Augmentative Releases ofCatolaccus grandis(Hymenoptera: Pteromalidae)

Augmentative releases ofCatolaccus grandis(Burks) were conducted in the Lower Rio Grande Valley of Texas in an attempt to suppress infestations of boll weevil,Anthonomus grandisBoheman, occurring in stands of “fallow-season” cotton (i.e., fields in violation of the 1 September stalk destruction deadline mandated by Texas law). In each of five release sites monitored during the study period (October, 1994–March 1995), augmentative releases ofC. grandiswere accompanied by an appreciable increase in the incidence of parasitized boll weevils (primarily third-stage larvae and pupae infesting abcised cotton squares) within a relatively brief time period. The relatively high incidence of host mortality caused byC. grandisin each release site was largely indispensible (i.e., would not have occurred in the absence of the parasite) and served to destroy significant numbers of immature boll weevils that appear to have been predisposed to successfully overwinter. The potential role of parasite augmentation in the management of the overwintering boll weevil population in southern Texas is discussed.     

Establishment and Dispersal ofUrophora affinis(Diptera: Tephritidae) andMetzneria paucipunctella(Lepidoptera: Gelechiidae) in Southwestern Virginia

Two European gall-producing insects,Urophora affinisFrfld. (Diptera: Tephritidae) andMetzneria paucipunctella(Zeller) (Lepidoptera: Gelechiidae) were introduced into Virginia in 1986 for biological control of spotted knapweed (Centaurea maculosaLam.). Adults ofU. affinis(n = 2625) andM. paucipunctella(n = 450) were released at two sites in Montgomery County, Virginia, and their populations were monitored yearly by dissecting spotted knapweed flower heads. Beginning in 1992, knapweed samples collected at various distances from the release sites were checked for dispersal.U. affinisis well established and is spreading slowly. The number of larvae per flower head and the seed numbers are inversely related as plants with the greatest number of larvae per spotted knapweed head had the lowest number of seeds. Knapweed density has declined at one of the release sites which had the highest rate of infestation byU. affinis.Establishment of the moth,M. paucipunctella,is less certain as it has been recovered at a very low level from only one site.     

Monitored releases of Rhinoncomimus latipes (Coleoptera: Curculionidae), a biological control agent of mile-a-minute weed (Persicaria perfoliata), 2004–2008

Mile-a-minute weed, Persicaria perfoliata (L.) H. Gross, is an invasive annual vine of Asian origin that has developed extensive monocultures, especially in disturbed open areas in the Mid-Atlantic region of the United States. A host-specific Asian weevil, Rhinoncomimus latipes Korotyaev, was approved for release in North America in 2004, and weevils have been reared at the New Jersey Department of Agriculture Beneficial Insect Laboratory since then. By the end of 2007 more than 53,000 weevils had been reared and released, mostly in New Jersey, but also in Delaware, Maryland, Pennsylvania, and West Virginia. The beetles established at 63 out of 65 sites (96.9%) where they were released between 2004 and 2007, with successful releases consisting of as few as 200 weevils. Weevils were recorded at 30 additional non-release sites in New Jersey, where they had dispersed at an average rate of 4.3 km/year. Standardized monitoring of fixed quadrats was conducted in paired release and control sites at eight locations. Significant differences in mile-a-minute weed populations in the presence and absence of weevils were found at three locations, with reduction in spring densities to 25% or less of what they had been at the start within 2–3 years at release sites, while weed densities at control sites were largely unchanged. Mile-a-minute weed populations at a fourth site were similarly reduced at the release site, but without control data for comparison due to rapid colonization of the paired control site. At the other four locations, all on islands, mile-a-minute weed populations were reduced at both release and control sites without large weevil populations developing, apparently due to environmental conditions such as late frost and extreme drought.     

Using molecular genetics to identify immature specimens of the weevil Ceratapion basicorne (Coleoptera: Apionidae)

Molecular analyses can play a primary role in the process of host specificity evaluation at species and population levels. Here we present an example of their application with a promising candidate biological control agent for yellow starthistle, Centaurea solstitialis L. Although it is highly host specific, Ceratapion basicorne (Coleoptera: Apionidae) can develop on safflower in laboratory tests. A field experiment was conducted to further evaluate host plant specificity; however, it was not possible to rear all larvae to the adult stage, which was necessary for species determination. Therefore molecular genetic methods were used to identify immature specimens. A 731 bp fragment of mtDNA cytochrome C oxidase I gene (COI) was sequenced from 41 individuals of C. basicorne and four congeners: Ceratapion orientale, Ceratapion onopordi, Ceratapion penetrans and Ceratapion scalptum. Intraspecific variability ranged from 0.0% to 0.2%, and interspecific divergences ranged from 1.7% to 17.6%. All larvae that were sequenced from the field study, clearly matched one of the five species, enabling us to unambiguously identify them. Use of molecular genetics to identify larvae should also help the process of foreign exploration, enabling the identification of field-collected larvae, which often provide more reliable host plant associations than field collected adults.     

Open field host selection and behavior by tamarisk beetles (Diorhabda spp.) (Coleoptera: Chrysomelidae) in biological control of exotic saltcedars (Tamarix spp.) and risks to non-target athel (T. aphylla) and native Frankenia spp.

Biological control of invasive saltcedars (Tamarix spp.) in the western U.S. by exotic tamarisk leaf beetles, Diorhabda spp., first released in 2001 after 15 years of development, has been successful. In Texas, beetles from Crete, Greece were first released in 2004 and are providing control. However, adults alight, feed and oviposit on athel (Tamarix aphylla), an evergreen tree used for shade and as a windbreak in the southwestern U.S. and México, and occasionally feed on native Frankenia spp. plants. The ability of tamarisk beetles to establish on these potential field hosts was investigated in the field. In no-choice tests in bagged branches, beetle species from Crete and Sfax, Tunisia produced 30–45% as many egg masses and 40–60% as many larvae on athel as on saltcedar. In uncaged choice tests in south Texas, adult, egg mass and larval densities were 10-fold higher on saltcedar than on adjacent athel trees after 2 weeks, and damage by the beetles was 2- to 10-fold greater on saltcedar. At a site near Big Spring, in west-central Texas, adults, egg masses and 1st and 2nd instar larvae were 2- to 8-fold more abundant on saltcedar than on athel planted within a mature saltcedar stand being defoliated by Crete beetles, and beetles were 200-fold or less abundant or not found at all on Frankenia. At a site near Lovelock, Nevada, damage by beetles of a species collected from Fukang, China was 12–78% higher on saltcedar than on athel planted among mature saltcedar trees undergoing defoliation. The results demonstrate that 50–90% reduced oviposition on athel and beetle dispersal patterns within resident saltcedar limit the ability of Diorhabda spp. to establish populations and have impact on athel in the field.     

Essential oils from the aerial parts of Centaurea cuneifolia Sibth. & Sm. and C. euxina Velen., two species growing wild in Bulgaria

The volatile constituents of the aerial parts of Centaurea cuneifolia Sibth. & Sm. and Centaurea euxina Velen. from Bulgaria were extracted by hydrodistillation and were analyzed. The main components in C. cuneifolia were β-eudesmol (26.5%) and hexadecanoic acid (17.6%). The main components in C. euxina were hexadecanoic acid (20.3%), spathulenol (10.8%) and caryophyllene oxide (6.2%). The chemotaxonomic significances with respect to other previously studied species of the same sections (Achrolopus and Phalolepis, respectively) are discussed.