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The local population dynamics of insect herbivores in ephemeral patches of short-lived plants are poorly known. We investigated whether a specialist and a generalist caterpillar exhibit contrasting temporal patterns of attack during plant development and also assessed bottom-up forces related to plant ontogeny that govern such population trends. Immature stages of the polyphagous Trichoplusia ni (Hübner) and the oligophagous Plutella xylostella (L.) were sampled throughout the development of cabbage (Brassica oleracea L. var. capitata L.) crops. We measured protein and glucosinolate contents and insect performance with regard to plant age and leaf strata. The populations of both caterpillar species changed in close parallel throughout plant development, and a nonlinear temporal pattern of egg laying was reproduced in sequential population patterns of the larval stages until pupation. Reduced protein availability and insect performance coincided with a decline in egg laying and subsequent larval abundance in mature plants. By standardizing the plant size, we found that young and nutritious plants support proportionately more insects than large and mature plants. In our models of the population oscillations, the interaction between plant size and quality provided a strong causal explanation for the densities of both oligophagous and polyphagous caterpillars. Patches of fast-growing herbaceous plants are very common worldwide in the form of crop fields, and a generalized temporal pattern of attack may be widespread among caterpillars, regardless of their feeding specialization. Our results highlight the role of bottom-up forces in shaping the population dynamics of caterpillars in such systems.
Commercial cucurbit production typically involves agriculturally intensive practices, with fields prepared using conventional tillage, plasticulture, and chemically based pestmanagement. Conservation-basedmanagement options are limited. In this study, we consider two alternative strategies, strip tillage and the use of row covers. We compare their impact on the beneficial carabid beetle (Coleoptera: Carabidae) community in melons and squash, following conventional or organic systems, over two years. Multivariate analysis demonstrated that soil management system (strip tillage versus plasticulture) was the primary variable influencing carabid distribution; row cover was a less important factor. The response to soilmanagement was species dependent. Some dominant species, such as Harpalus pensylvanicus DeGeer, demonstrated no preference for a particular soil treatment. For others, including the tiger beetle, Cicindela punctulata Olivier, and a slug predator, Chlaenius tricolor Dejean, activity–density was higher in strip-tillage production systems. Our analysis suggested that strip-tillage production systems support a richer, more diverse carabid community. These results demonstrate that even within intensive annual horticultural systems, production practices can play a critical role in shaping the beneficial arthropod community, potentially encouraging or limiting ecosystem services.
Substrates composed of hay residues, dung, and urine accumulate around winter hay feeding sites in cattle pastures, providing developmental habitats for stable flies. The objective of this study was to relate physiochemical and microbial properties of these substrates to the presence or absence of stable fly larvae. Properties included pH, temperature, moisture, ammonium concentration, electrical conductivity, and numbers of coliform, fecal coliform, Escherichia coli, and Enterococcus bacteria. Each physiochemical sample was classified as a function of belonging to one of the three 2-m concentric zones radiating from the feeder as well as presence or absence of larvae. In total, 538 samples were collected from 13 sites during 2005–2011. Stable fly larvae were most likely to be found in moist, slightly alkaline substrates with high levels of ammonium and low temperature. The probability of larvae being present in a sample was the highest when the moisture content was 347% relative to dry weight and the average pH was 8.4. Larvae were recovered within all zones, with a nonsignificant, but slightly higher, percentage of samples containing larvae taken 2–4m from the center. All methods used to enumerate bacteria, except total coliform, indicated decreasing concentrations in hay bale residue throughout the summer. In addition to the environmental parameters, cumulative degree day 10°C had a significant effect on the probability of observing stable fly larvae in a sample, indicating that unidentified seasonal effects also influenced immature stable fly populations.
Termites are a key functional group in the forest ecosystem, but they damage trees. To investigate the termite infestation pattern on the whole tree, we cut 108 blackboard trees, Alstonia scholaris (L.) R. Br., and 50 Japanese cedars, Cryptomeria japonica (L. f.) D. Don, into sections. The bark surface and cross sections of the tree trunk were examined along the axes. A high percentage of blackboard trees (92.6%) was infested by fungus-growing termites, Odontotermes formosanus (Shiraki), but damage was limited to the bark surface at a 2-m height. The infestation rate of dampwood termites, Neotermes koshunensis (Shiraki), was only 4.6% (5/108), and all infestations were associated with trunk wounds. N. koshunensis was found at significantly higher portion of a tree than O. formosanus. Among 50 Japanese cedars, 20 living trees were not infested by any termites, but 26 of the 30 dead trees were infested by subterranean termites, Reticulitermes flaviceps (Oshima), which excavated tunnels in the trunk. The infestation rate at basal sections was higher than that at distal sections. Only one Japanese cedar tree was infested by another dampwood termite, Glyptotermes satsumensis (Matsumura). The two dominant termite species, O. formosanus and R. flaviceps, had subterranean nests and infested trees from bottom up. The two primitive termites N. koshunensis and G. satsumensis had low infestation rates and are most likely to infest trees by alates from top down. The niche segregation in trees of three termite families, Kalotermitidae, Rhinotermitidae, and Termitidae, was distinct.
When related species coexist, selection pressure should favor evolution of species recognition mechanisms to prevent interspecific pairing and wasteful reproductive encounters. We investigated the potential role of pheromone and acoustic signals in species recognition between two species of tree-killing bark beetles, the southern pine beetle, Dendroctonus frontalis Zimmermann, and the western pine beetle, Dendroctonus brevicomis LeConte, in a narrow zone of sympatry, using reciprocal pairing experiments. Given the choice of adjacent con- or heterospecific female gallery entrance in a log, at least 85% of walking males chose the entrance of the conspecific, and half the males that initially entered heterospecific galleries re-emerged and entered the conspecific gallery within 15 min. Waveform analysis of female acoustic “chirps” indicated interspecific differences in chirp timing. Males may use information from female acoustic signals to decide whether to enter or remain in the gallery. Individuals in forced heterospecific pairings (produced by confinement of a heterospecific male within the female entrance) did not differ in pheromone production from individuals of conspecific pairs. However, due to the absence of the right species of male, galleries with heterospecific pairs released an abnormal pheromone blend that lacked at least one key component of the aggregation pheromone of either species. The complete aggregation pheromone (i.e., the pheromone blend from entrances with pairs) does not appear to deter interspecific encounters or confer premating reproductive isolation per se; however, it may confer selective pressure for the maintenance of other reproductive isolation mechanisms.
Urban gardens may preserve biodiversity as urban population densities increase, but this strongly depends on the characteristics of the gardens and the landscapes in which they are embedded. We investigated whether local and landscape characteristics are important correlates of bee (Hymenoptera: Apiformes) abundance and species richness in urban community gardens. We worked in 19 gardens in the California central coast and sampled bees with aerial nets and pan traps. We measured local characteristics (i.e., vegetation and ground cover) and used the USGS National Land Cover Database to classify the landscape surrounding our garden study sites at 2 km scales. We classified bees according to nesting type (i.e., cavity, ground) and body size and determined which local and landscape characteristics correlate with bee community characteristics. We found 55 bee species. One landscape and several local factors correlated with differences in bee abundance and richness for all bees, cavity-nesting bees, ground-nesting bees, and different sized bees. Generally, bees were more abundant and species rich in bigger gardens, in gardens with higher floral abundance, less mulch cover, more bare ground, and with more grass. Medium bees were less abundant in sites surrounded by more medium intensity developed land within 2 km. The fact that local factors were generally more important drivers of bee abundance and richness indicates a potential for gardeners to promote bee conservation by altering local management practices. In particular, increasing floral abundance, decreasing use of mulch, and providing bare ground may promote bees in urban gardens.
Anagrus erythroneurae S. Trjapitzin & Chiappini and Anagrus daanei Triapitsyn are the key parasitoids of the western grape leafhopper (Erythroneura elegantula Osborn) in northern California vineyards. Erythroneura elegantula overwinters as an adult in reproductive diapause. To successfully overwinter, Anagrus spp. must locate an alternate leafhopper host that overwinters in an egg stage that they can parasitize. These alternate leafhopper hosts are thought to be primarily located in the natural habitats surrounding vineyards. This study identifies the noncrop host plants utilized by Anagrus spp. not only during the overwintering period but throughout the entire year, as well as the leafhopper species associated with these host plants. Over a 2-yr period, Anagrus spp. and leafhoppers were sampled from numerous plants in natural and cultivated habitats surrounding vineyards. Results from this study confirm previously known Anagrus spp. host plants, but also identify new host plant species. Some of the host plants harbored Anagrus spp. year-round while others were utilized only during certain periods of the year. Leafhoppers associated with Anagrus spp. host plants may potentially serve as the alternate host utilized by Anagrus spp. on these plants, but this was not confirmed in the current study. Records of E. elegantula demonstrate their cyclical movement between the vineyard floor (winter), temporary noncrop hosts (spring/fall), and the grape vine canopy (summer).
Emerald ash borer (Agrilus planipennis Fairmaire), an invasive wood-boring beetle native to Asia, has killed hundreds of millions of ash trees since its accidental introduction into North America, resulting in widespread formation of canopy gaps and accumulations of coarse woody debris (CWD) in forests. The objective was to quantify effects of canopy gaps and CWD caused by early stages of emerald ash borer-induced ash mortality, and their interaction on ground beetle assemblages. The impact of canopy gaps and CWD varied, as gaps affected beetle assemblages in 2011, while effects of CWD were only observed in 2012. Gaps decreased beetle activity-abundance, and marginally decreased richness, driving changes in species composition, but evenness and diversity were unaffected. Effects of the CWD treatment alone were minimal, but CWD interacted with the canopy treatment, resulting in an increase in activity-abundance of ground beetles in canopy gaps without CWD, and a marginal increase in species richness in canopy gaps with CWD. Although there were some initial changes in species composition, these were ephemeral, suggesting that ground beetle assemblages may be resilient to disturbance caused by emerald ash borer. This study contributes to our understanding of the cascading ecological impacts of biological invasions on forest ecosystems.
Hypothenemus are some of the most common and diverse bark beetles in natural as well as urban habitats, particularly in tropical and subtropical regions. Despite their ecological success and ubiquitous presence, very little is known about the habits of this genus. This study aimed to understand species diversity and daily and seasonal trends in host-seeking flight patterns of Hypothenemus in a suburban environment by systematic collections with ethanol baiting over a 15-mo period in South Florida. A total of 481 specimens were collected and identified as eight species, most of them nonnative. Hypothenemus formed the overwhelming majority of bark beetles (Scolytinae) collected, confirming the dominance of the genus in urban environments. Hypothenemus brunneus (Hopkins) and Hypothenemus seriatus (Eichhoff) were most abundant, comprising 74% of the capture. Rarefaction showed that the sample was sufficient to characterize the local diversity and composition. The seasonal pattern in Hypothenemus capture was positively correlated to day-time temperature, not to season as in most temperate Scolytinae. Another significant observation in the community dynamics was the synchronized occurrence of two common species (H. birmanus and H. javanus), unrelated to season. Hypothenemus were predominantly diurnal with a broad flight window. Females flew as early as 11: 00 hours (EDST), with peak flight occurring at 15: 00 hours, significantly earlier than flight patterns of most other Scolytinae. Surprisingly, male Hypothenemus were frequently collected, despite their lack of functional wings. Several potential explanations are discussed. This is the first study into the ecology of an entire community of the twig-feeding Hypothenemus.
The Karner blue butterfly (Lycaeides melissa samuelis Nabokov) (Lepidoptera: Lycaenidae) is a federally listed, endangered species that has experienced dramatic decline over its historic range. In surviving populations, Karner blue butterflies have a facultative mutualism with ants that could be critically important to their survival where their populations are threatened by habitat loss or disturbance. In this study, we investigated the effects of ants, wild blue lupine population status (native or restored), and fire on adult Karner blue butterfly abundance at the Concord Pine Barrens, NH, USA. Ant frequency (the number of times we collected each ant species in our pitfall traps) was higher in restored than native lupine treatments regardless of burn status during both Karner blue butterfly broods, and the trend was statistically significant during the second brood. We observed a positive relationship between adult Karner blue butterfly abundance and ant frequency during the first brood, particularly on native lupine, regardless of burn treatment. During the second brood, adult Karner blue butterfly abundance and ant frequency were not significantly correlated in any treatments or their combinations. Our findings suggest that a combination of native and restored lupine is important for supporting both Karner blue butterflies and ants at the Concord Pine Barrens, and that burning does not affect the mutualism. Thus, scientists and managers at the site may wish to target their habitat management activities to best support both Karner blue butterflies and the particular ant species that provide the greatest benefit to their survival.
It is broadly known that the conservation of biological diversity in agricultural ecosystems contributes to pest control. This process was studied in a prickly pear plantation (Opuntia megacantha and Opuntia ficus-indica) located in central Mexico. No insecticides have been used on this plantation since 2000, and local farmers believe that the presence of different species of insects limits the growth of the wild cochineal (Dactylopius opuntiae Cockerell), which is one of the main pests in this crop. From August 2012 to November 2013, we estimated the number of cochineal per stem in the plantation and determined its spatial distribution pattern. In order to identify signs of population regulation, we obtained histograms of the frequency distribution of the size of the clusters and determined if distribution is adjusted to a power function (power law). We identified the cochineal predators and determined the correlation in their abundances. The greater abundance of cochineal occurred between summer and autumn while the minimum value was recorded in spring. The frequency distribution of the cochineal clusters had a high level of adjustment to a power function, suggesting the presence of population regulation processes. Six species that prey on cochineal were identified. Laetilia coccidivora and Hyperaspis trifurcata were the most active and their abundance was significantly correlated with the abundance of cochineal. We found that the probability of extinction of these insects in a cladode increases with its density, since the density and predator activity also increased. It is likely that, under these conditions, the cochineal have established an autonomous control.
Incorporating nonprey sugar resources into apple orchards is a potential means of enhancing biological control services, but little is known about the impacts of extrafloral nectars on aphidophagous coccinellids. We explored peach Prunus persica (L.) Batsch extrafloral nectar as a supplemental resource for Harmonia axyridis (Pallas), a key aphid predator in the mid-Atlantic United States. Extrafloral nectar quantity, temporal production, and carbohydrate profile were assessed for four peach cultivars in orchard and greenhouse culture. Seasonal densities of H. axyridis visiting extrafloral nectaries were estimated, and the propensity of beetles to feed upon extrafloral nectar was compared by cultivar in the laboratory. We also compared survival of newly eclosed adult pairs that were starved or fed aphids with or without extrafloral nectar. Peach extrafloral nectar contained six carbohydrates, with sucrose dominant for all cultivars, but extrafloral nectar production varied significantly by cultivar and collection date, with ‘Lovell’ yielding higher average seasonal volume than the other cultivars. Harmonia axyridis continuously foraged on peach trees lacking prey, and beetle abundance was positively correlated with the number of leaves actively producing extrafloral nectar. In laboratory assays, newly emerged adult beetles preferentially selected and consumed extrafloral nectar of Lovell peach shoots. Furthermore, when prey were initially unavailable to adult H. axyridis, the beetles were sustained by extrafloral nectar and experienced longer survival compared with beetles without the supplemental resource. Collectively, these results suggest that peach extrafloral nectar is a beneficial resource that could potentially sustain H. axyridis in orchards when prey are scarce.
Interactions among seed-feeding insects are well noted in the literature, with many of these interactions being asymmetrical and causing a disadvantage for one of the species involved. While often effective, the use of the cumulative stress approach to biological control (where multiple natural enemy species are released) may increase the risk of interaction, which may lead to less effective biological control programs. Spotted knapweed (Centaurea stoebe ssp. micranthos (Gugler) Hayek) is an invasive plant that causes damage in rangelands and pastures. In Arkansas, two biological control agents for spotted knapweed, Larinus minutus Gyllenhal and Urophora quadrifasciata Meigen, are established. Both species attack the capitula of spotted and diffuse knapweeds. There is potential for interactions between these species, and this could affect the efficacy of the biological control program. To evaluate these potential interactions, we collected spotted knapweed capitula weekly from three sites in Arkansas from 2010 to 2012. Capitula were monitored for emergence of L. minutus and U. quadrifasciata, and the effect on seed reduction was analyzed. Over all three years, L. minutus and U. quadrifasciata were present in 35.8% (492) and 22.8% (313) of the capitula, respectively. We determined that the occurrences of L. minutus and U. quadrifasciata were not independent of each other, and that L. minutus is more effective at reducing spotted knapweed seed production than U. quadrifasciata within individual capitula. Seed production in capitula with both natural enemies present was no different from capitula with L. minutus.
Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is a highly polyphagous invasive species and an important pest of orchard crops in the United States. In the Mid-Atlantic region, wild hosts of H. halys are common in woodlands that often border orchards, and H. halys movement from them into orchards poses ongoing management issues. To improve our understanding of host plant effects on H. halys populations at the orchard–woodland interface, nymphal survivorship, developmental duration, and adult fitness (size and fresh weight) on apple (Malus domestica Borkh.), peach (Prunus persica (L.) Batsch), Tree of Heaven (Ailanthus altissima (Mill.) Swingle), and northern catalpa (Catalpa speciosa (Warder)) were examined in laboratory studies. Specifically, we investigated nymphal performance on the foliage and fruiting structures of those hosts and on single- versus mixed-host diets, as well as the effects of host phenology on their suitability. Nymphal performance was poor on a diet of foliage alone, regardless of host. When fruiting structures were combined with foliage, peach was highly suitable for nymphal development and survivorship, whereas apple, Tree of Heaven, and catalpa were less so, although nymphal survival on Tree of Heaven was much greater later in the season than earlier. Mixed-host diets yielded increased nymphal survivorship and decreased developmental duration compared with diets of suboptimal single hosts. Adult size and weight were generally greater when they developed from nymphs reared on mixed diets. The implications of our results to the dispersal behavior, establishment, and management of H. halys are discussed.
In multivoltine insects that oviposit and develop on short-lived plants, different herbivore generations across a growing season often exploit different plant species. Here, we compare the development time, pupal mass, and survival of two closely related oligophagous herbivore species on two species of brassicaceous plants that grow in different habitats and which exhibit little overlap in temporal growth phenology. In central Europe, the green-veined white butterfly, Pieris napi L., is bivoltine, whereas the small cabbage white butterfly, Pieris rapae L., has two to three generations a year. Moreover, P. napi is primarily found in moist, open (e.g., meadow), and forest habitats, whereas P. rapae prefers drier, open habitats. Both butterflies were reared on Garlic mustard (Alliaria petiolata), which is shade-tolerant and grows early in spring in forest undergrowth, and Black mustard (Brassica nigra), which prefers open disturbed habitats and is most common in summer. Both host plant species differ in other traits such as secondary chemistry. We hypothesized that, owing to habitat preference, P. napi would develop equally well on both plants but that P. rapae would perform better on B. nigra. The results provide partial support for this hypothesis, as both herbivores performed equally well on A. petiolata and B. nigra. However, there were differences in these parameters that were species-specific: on both plants P. rapae developed faster and had larger pupae than P. napi. Our results show that specialized herbivores can exploit different species of related plants that grow at different times of the season, enabling them to have multiple generations.
Pickleworm, Diaphania nitidalis Cramer (Lepidoptera: Crambidae), is a major pest of cucurbits. The current management approach for this pest is weekly insecticide applications. A push–pull cropping approach may be an alternative management practice and could reduce reliance on pesticides. One potential push–pull scenario is the use of squash (Cucurbita pepo L.) as a trap crop and watermelon (Citrullus lanatus [Thunb.] Matsum. & Nakai) as a deterrent intercrop to manage pickleworm on cantaloupe (Cucumis melo L.). This study investigated if the underlying mechanism required for the success of this management approach (a female oviposition preference or nonpreference among squash, cantaloupe, and watermelon) is present. A series of oviposition preference experiments was conducted to see how individual females responded when presented with different host plants for oviposition. Under laboratory conditions, when females had the choice of a leaf from squash, cantaloupe, and watermelon, they laid a higher proportion of their eggs on the cantaloupe leaf. However, under greenhouse conditions, when females were presented with whole plants of the three different species, they laid a higher percent of their eggs on the squash plant. Females laid a similar number of eggs on watermelon as compared with cantaloupe under greenhouse conditions, and appeared to not be averse to laying their eggs on watermelon. However, when presented with a noncucurbit, such as bean, females laid a low number of total eggs. Overall, it appears that squash may be more preferred as an oviposition substrate than cantaloupe or watermelon and may be a useful trap crop or pull. Further study to determine a suitable deterrent intercrop or push and evaluation of the proposed system under field conditions are needed.
Lippia alba (Mill.) N.E. Br. ex Britton & P. Wilson (Verbenaceae) is a herbal aromatic shrub with medicinal properties. Natural populations of this species are allogamous and self-incompatible. Therefore, this plant species relies on pollinators to outcross and maintain the genetic variability. Here, we investigated the floral phenology, pollen morphology, the floral visitor entomofauna, and the influence of climatic factors on the frequency of visits in L. alba flowers. The study was conducted at Federal University of Juiz de Fora Plant Experimental Area, southeast Brazil. The flowering of L. alba occurred throughout the whole year. The anthesis is diurnal and lasts 5 d. The nectar guide was visible from the onset of flowering until the third day. Pollen grains were classified as isopolar, oblate spheroidal, three-colporate (rare, four-colporate), surface tectate-perforate, and endoaperture lalongate, with median constriction. Insects from the order Hymenoptera were the most frequent visitors observed, followed by Lepidoptera, Thysanoptera, Diptera, and Hemiptera–Heteroptera. The preference of insects for flowers with nectar guides shows that the color is likely to be an important visual trait to increase the frequency of visits. Moreover, the climate variables temperature, relative humidity, wind speed, and light were important to define the composition of the most frequent floral visitors.
Intercropping can reduce agricultural pest incidence, and represents an important sustainable alternative to conventional pest control methods. Understanding the ecological mechanisms for intercropping could help optimize its use, particularly in tropical systems which present a large number of intercropping possibilities. Citrus is threatened worldwide by greening disease (huanglongbing, HLB) vectored by the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae). Control of HLB and citrus psyllid can be partially achieved through intercropping with guava, Psidium guajava L., but the mechanisms remain unclear. We tested the hypothesis that guava olfactory cues affect psyllid behavior by altering the attractiveness of citrus through plant–plant interactions. In choice and no-choice cage experiments, psyllid settlement was reduced on citrus shoots that had been exposed to guava shoot odors for at least 2 h. In Y-tube olfactometer experiments, psyllids oriented to odors of unexposed, compared with guava-exposed, citrus shoots. These behavioral results indicate that a mechanism for the success of guava intercropping for sustainable, ecological disease management may be the indirect effect of guava on citrus attractiveness.
Low-density per ha “meso” dispensers loaded with pear ester, ethyl (E,Z)-2,4-decadienoate, kairomone and codlemone, (E,E)-8,10-dodecadien-1-ol, pheromone of codling moth, Cydia pomonella (L)., were evaluated versus meso dispensers loaded with pheromone alone for mating disruption control in walnut orchards receiving no insecticide sprays. Meso dispensers loaded with codlemone alone (Ph meso) were applied at 50 ha–1 and compared with mesos combining codlemone and pear ester (Ph + PE meso) at 25 and 50 ha–1. Various lures containing pear ester (PE), Ph–PE combo, and an experimental codlemone plus (E)-4,8-dimethyl-1,3,7-nonatriene lure were tested alone and with acetic acid (AA) lures for moth capture efficacy. Male moth capture in pheromone traps was significantly reduced by 88% in Ph meso plots and 96% in Ph + PE meso plots versus control plots. Moth capture in Ph–PE combo traps was significantly reduced for both sexes in all meso plots. Harvest damage by both the codling moth and the secondary pest, navel orangeworm, Amyelois transitella (Walker), was significantly lower in all meso treatment plots compared with damage in control plots. Nut injury level with the Ph + PE meso treatment (50 ha–1) was significantly lower than in Ph meso plots for both codling moth and combined pest injury. Regression analysis suggested that nut infestation levels by navel orangeworm were influenced by codling moth levels. In all meso plots, the most effective lures attracting both codling moth sexes were PE & AA or Ph–PE combo & AA. Demonstrated disruption and control efficacy of these pheromone plus PE-meso dispensers applied at low densities supports development of the meso dispenser tactic for practical pest management use in walnut orchards with inherent low planting densities.
Research on phytoseiid mites has been critical for developing an effective biocontrol strategy for suppressing Oligonchus perseae Tuttle, Baker, and Abatiello (Acari: Tetranychidae) in California avocado orchards. However, basic understanding of the spatial ecology of natural populations of phytoseiids in relation to O. perseae infestations and the validation of research-based strategies for assessing densities of these predators has been limited. To address these shortcomings, cross-sectional and longitudinal observations consisting of >3,000 phytoseiids and 500,000 O. perseae counted on 11,341 leaves were collected across 10 avocado orchards during a 10-yr period. Subsets of these data were analyzed statistically to characterize the spatial distribution of phytoseiids in avocado orchards and to evaluate the merits of developing binomial and enumerative sampling strategies for these predators. Spatial correlation of phytoseiids between trees was detected at one site, and a strong association of phytoseiids with elevated O. perseae densities was detected at four sites. Sampling simulations revealed that enumeration-based sampling performed better than binomial sampling for estimating phytoseiid densities. The ecological implications of these findings and potential for developing a custom sampling plan to estimate densities of phytoseiids inhabiting sampled trees in avocado orchards in California are discussed.
Aphelinus asychis Walker (Hymenoptera: Aphelinidae), a polyphagous parasitoid, has been widely used as a biological control agent against Myzus persicae (Sulzer) (Hemiptera: Aphididae) and other aphid species. In order to ensure the successful biological control of M. persicae, we evaluated the influence of brief heat stresses (32.5, 35.0, 37.5, 40.0, and 41.5°C for 1 h), which occur frequently during the summer or under greenhouse conditions, on survival, longevity, host feeding, and parasitism of A. asychis that were reared on chili pepper at 25°C in the laboratory. Our results showed several major consequences on the parasitoid adults after brief heat stress. First, the survival of briefly heat stress-treated A. asychis female and male adults decreased significantly at ≥37.5°C and their longevity decreased as well. Second, the number of M. persicae nymphs infesting chili pepper killed through host feeding by the treated A. asychis females decreased significantly. Third, the cumulative number of mummified aphids and female progeny produced by the treated A. asychis also decreased significantly at ≥37.5°C. Our results indicated that a brief heat stress on A. asychis adults caused severe effects on major life history traits and total numbers of hosts killed by host feeding and parasitism, suggesting that high temperatures should be avoided to ensure the success of biological control of M. persicae and other aphid species using this parasitoid species.
Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) is a solitary egg parasitoid of the invasive emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), and has been introduced to the United States for classical biological control. We characterized the weekly survivorship, fecundity, and diapause patterns of both diapaused and nondiapaused populations of O. agrili under four different temperature–photophase combinations: 30°C (warm) and 20°C (cold) temperatures with both long-day (16 h) and short-day (8 h) photophase. Results of this study showed that regardless of the length of photophase, parental parasitoids of both diapaused and nondiapaused O. agrili survived significantly longer at 20°C than at 30°C. Both populations also laid their eggs faster at 30°C compared with those at 20°C. Higher proportions of the progeny produced by both populations of O. agrili were induced into diapause by short-day (8 h) photophase, regardless of rearing temperature. In addition, the diapaused parasitoids in the short-day photophase treatment at both warm and cold temperatures produced increasing proportions of diapaused progeny over time, whereas no significant differences were observed in the proportions of diapaused progeny by the nondiapaused parasitoids over different sampling times. These findings suggest that O. agrili should be continuously reared under warm temperature and long-day photoperiod (to avoid diapause for increased reproduction). In addition, we recommend that diapaused adults be used for field releases in early summer when temperatures are still relatively low (∼20°C) and host eggs are available so that they can produce multiple generations prior to overwintering.
Degree-day models link ambient temperature to the development of insects, making such models valuable tools in integrated pest management. These models increase management efficacy by quantifying and predicting pest phenology. In Wisconsin, the top insect pest of cranberry production is the cranberry fruitworm, Acrobasis vaccinii Riley (Lepidoptera: Pyralidae). Control of this species is often complicated by the fact that the larvae feed entirely within the fruit. Timing of control tactics, therefore, is critical and generally targets the adult and egg stages. However, the commencement of oviposition and egg hatch are extremely difficult to track empirically, forcing pest management strategies to rely on proxy events that are more apparent but less informative as indicators of cranberry fruitworm egg presence. This research provides the upper and lower temperature-mediated growth thresholds of this pest, which represents the first steps toward the creation of a degree-day model. Using field-collected A. vaccinii, we reared the larvae within cranberry fruit and monitored larval growth at nine different constant temperatures. We determined the average growth rate at each temperature and modeled growth rates as a function of temperature. We then calculated the precise upper and lower developmental temperature thresholds of this species. Future work will be able to use these thresholds to generate degree-day accumulations that correspond to phenological events in the field, providing a powerful predictive tool for pest management in cranberry production.
The insect Uvarovites inflatus Uvarov is highly appreciated in China. It is known for its distinctive songs and horn-like forewings and is raised commercially for insect lovers. U. inflatus was previously categorized as part of the monotypic genus Uvarovites; however, there was little molecular evidence to support this taxonomic classification. This study obtained and investigated the mitogenome of U. inflatus, and its songs were characterized and compared with other Ensifera species whose mitogenomes are available. By performing the mitochondrial analysis, we were able to assess the phylogenetic relationships between these species and discuss the evolution of Ensifera calling songs. The mitogenome of U. inflatus is 15,956 bp in length and contains 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and 1 control region. The organization and orientation of the U. inflatus mitogenome are similar to those of other Tettigonioidea species. Phylogenetic analysis based on 13 protein-coding genes showed that the superfamily Tettigonioidea is monophyletic, as are the other six tested subfamilies from Tettigonioidea. Our results also indicated that Grylloidea is monophyletic. A Bayesian relaxed clock analysis showed that the differentiation of U. inflatus and Gampsocleis gratiosa Brunner occurred in the middle Miocene, suggesting that their speciation occurred over a long evolutionary period. The results provide significant support for the establishment of the monotypic genus Uvarovites. Calling song analysis showed that at least two discrete steps of independent evolution occurred during the change from pure tone to broadband noise, and that the ancestor of existing Ensifera was more likely to have emitted pure-tone songs than broadband signals. Together, the mitogenome, molecular clock, and acoustic data allowed us to clarify the taxonomic state of U. inflatus and propose a timeline for the evolution of Ensifera songs.
Recent detection of western corn rootworm resistance to Bt (Bacillus thuringiensis) corn prompted recommendations for the use of integrated pest management (IPM) with planting refuges to prolong the durability of Bt technologies. We conducted a simulation experiment exploring the effectiveness of various IPM tools at extending durability of pyramided Bt traits. Results indicate that some IPM practices have greater merits than others. Crop rotation was the most effective strategy, followed by increasing the non-Bt refuge size from 5 to 20%. Soilapplied insecticide use for Bt corn did not increase the durability compared with planting Bt with refuges alone, and both projected lower durabilities. When IPM participation with randomly selected management tools was increased at the time of Bt commercialization, durability of pyramided traits increased as well. When non-corn rootworm expressing corn was incorporated as an IPM option, the durability further increased.
For corn rootworm, a local resistance phenomenon appeared immediately surrounding the resistant field (hotspot) and spread throughout the local neighborhood in six generations in absence of mitigation. Hotspot mitigation with random selection of strategies was ineffective at slowing resistance, unless crop rotation occurred immediately; regional mitigation was superior to random mitigation in the hotspot and reduced observed resistance allele frequencies in the neighborhood. As resistance alleles of mobile pests can escape hotspots, the scope of mitigation should extend beyond resistant sites. In the case of widespread resistance, regional mitigation was less effective at prolonging the life of the pyramid than IPM with Bt deployment at the time of commercialization.
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