Tissue distribution and characterization of predominant hemolymph carrier proteins from Dermacentor variabilis and Ornithodoros parkeri

The tissue distribution of the predominant hemolymph protein found throughout tick development was examined in the hard tick, Dermacentor variabilis, and in the soft tick, Ornithodoros parkeri. In D. variabilis, the predominant (purified) hemolymph protein was a lipoglycoheme-carrier protein (DvCP) with a molecular weight of 200 K. A protein with a similar mobility on native-PAGE was found in fat body, salivary gland, muscle and ovary from partially fed females which was most abundant in the plasma and salivary gland. DvCP from plasma, salivary gland and fat body of partially fed females consisted of two subunits on SDS-PAGE (98 and 92 K). In replete females, only salivary gland exhibited protein subunits equivalent to hemolymph CP. CP in salivary gland and fat body stained positive for lipids. The concentration of CP in tissues varied between partially fed and replete females, indicating a difference in the expression and/or sequestration of CP during adult development. The predominant hemolymph carrier protein from O. parkeri (OpCP) was purified to homogeneity for the first time and is presumed to have similar functions to CP from D. variabilis. Purified OpCP exhibited a molecular weight of 668 K by native-PAGE. Unlike CP from D. variabilis, OpCP was not detected in fat body or salivary gland tissues but occurred abundantly in coxal fluid. By SDS-PAGE, purified hemolymph OpCP consisted of two major subunits (114 and 93 K) and a less abundant protein with an apparent molecular weight of 48 K. Purified native OpCP was a lipoprotein like DvCP. A spectral analysis of purified OpCP failed to demonstrate the presence of heme like that found for CP from D. variabilis, purified by the same methods. However, plasma from O. parkeri contained heme with a λ_max of 410 nm.     

Histamine release factor from Dermanyssus gallinae (De Geer): characterization and in vitro assessment as a protective antigen

A cDNA encoding a 174-amino-acid orthologue of a tick histamine release factor (HRF) was identified from the haematophagous poultry red mite Dermanyssus gallinae. The predicted D. gallinae HRF protein (Dg-HRF-1) sequence is highly conserved with the tick HRFs (identity 52-54%) and to a lesser degree with translationally controlled tumour proteins (TCTP) from mammals and other invertebrates (range 38-47%). Phylogenetically, Dg-HRF-1 partitions with the tick HRF clade suggesting a shared linage and potentially similar function(s). A recombinant Dg-HRF-1 protein (rDg-HRF-1) was produced and shown to induce degranulation of rat peritoneal mast cells in vitro, confirming conservation of the histamine-releasing function in D. gallinae. Polyclonal antibodies were generated in rabbits and hens to rDg-HRF-1. Western blotting demonstrated that native Dg-HRF is a soluble protein and immunohistochemical staining of mite sections revealed that the distribution of Dg-HRF, although ubiquitous, is more common in mite reproductive, digestive and synganglion tissues. A survey of hens housed continuously in a mite-infested commercial poultry unit failed to identify IgY specific for recombinant or native Dg-HRF, indicating that Dg-HRF is not exposed to the host during infestation/feeding and may therefore have potential as a vaccine using the concealed antigen approach. To test the protective capability of rDg-HRF-1, fresh heparinised chicken blood was enriched with yolk-derived anti-Dg-HRF IgY antibodies and fed to semi-starved mites using an in vitro feeding system. A statistically significant increase in mortality was shown (P = 0.004) in mites fed with anti-Dg-HRF IgY after just one blood meal. The work presented here demonstrates, to our knowledge for the first time, the feasibility of vaccinating hens with recombinant D. gallinae antigens to control mite infestation and the potential of rDg-HRF-1 as a vaccine antigen.     

Overwintering Mite Diversity and Their Habitats in Apple and Pear Orchards of Korea with Emphasis on Phytoseiidae and Tetranychidae

Overwintering mite diversity and their habitats were studied in apple and pear orchards during 2002-2003 winter season. Twospotted spider mite was mostly found under the tree barks and fabric strips. European red mites were from crevices of twigs. Tydeid, tarsonemid and oribatid mites were mostly from soil and ground vegetation. Even in the protected overwintering habitat such as artificial fabric strip, twospotted spider mite suffered 81-91% mortality during winter. Predaceous phytoseiid mites found were Amblyseius womersleyi, A. makuwa, A. orientalis, A. rademacheri A. obtuserellus, and A. eharai. Amblyseius womersleyi was the most dominant species in both apple and pear orchards, followed by A. obtuserrellus in apple orchards and A. makuwa in pear orchards. Most phytoseiid mites were found on ground vegetation while their potential prey items were remained on the tree. Implication of the findings for conservation of beneficial mites and biological control of spider mite during season was further discussed.     

Evaluation of predatory mites and Acramite for control of twospotted spider mites in strawberries in north central Florida

Greenhouse and field experiments were conducted from 2003 to 2005 to determine the effectiveness of two predatory mite species, Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus (McGregor), and a reduced-risk miticide, Acramite 50 WP (bifenazate), for control of twospotted spider mite, Tetranychus urticae Koch, in strawberries (Fragaria x ananassa Duchesne). In greenhouse tests, three treatments consisting of releases of P. persimilis, N. californicus, and an untreated control were evaluated. Both species of predatory mites significantly reduced twospotted spider mite numbers below those found in the control during the first 3 wk of evaluation. However, during week 4, twospotted spider mite numbers on the plants treated with P. persimilis increased and did not differ significantly from the control. Field studies used releases of P. persimilis and N. californicus, applications of Acramite, and untreated control plots. Both N. californicus and P. persimilis significantly reduced populations of twospotted spider mite below numbers recorded in the control plots. During the 2003-2004 field season P. persimilis took longer than N. californicus to bring the twospotted spider mite population under control (< 10 mites per leaflet). Acramite was effective in reducing twospotted spider mite populations below 10 mites per leaflet during the 2003-2004 field season but not during the 2004-2005 field season, possibly because of a late application. These findings indicate that N. californicus releases and properly timed Acramite applications are promising options for twospotted spider mite control in strawberries for growers in north Florida and other areas of the southeast.     

Effects of soil moisture and temperature on reproduction and development of twospotted spider mite (Acari: Tetranychidae) in strawberries

The effects of soil moisture and temperature on the reproduction of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), were examined in laboratory and field tests in strawberries, Fragaria x ananassa Duchesne, in Florida. Different soil moisture levels (low, moderate, and high) were compared to determine how soil moisture affects the reproduction and development of twospotted spider mite. In addition to soil moisture, different irrigation techniques (drip versus drip/overhead) were compared to determine their effects on twospotted spider mite reproduction as well as the incidence of angular leaf spot, Xanthomonas fragaria Kennedy & King disease. Similar studies were conducted to determine how different temperatures (18, 27, and 35 degrees C) affect the reproduction and development of twospotted spider mites. In the laboratory, low soil moisture as well as temperatures >27 degrees C promoted twospotted spider mite development. A similar trend was observed in a field study with low soil moisture promoting twospotted spider mite reproduction during the early season (11 November--8 December). Irrespective of moisture levels, a significantly higher incidence of X. fragaria was recorded in treatments with drip/overhead irrigation systems compared with drip irrigation. Implications for management of soil moisture levels are discussed with respect to the abundance of twospotted spider mite and X. fragaria in strawberries.     

Spatial distribution of predators and prey affect biological control of twospotted spider mites by Phytoseiulus persimilis in greenhouses

We evaluated the effects of predator release pattern and prey distribution on rate of suppression of the twospotted spider mite, Tetranychus urticae Koch (Acari, Tetranychidae) and visual damage to the ornamental plant, Impatiens wallerana Hook.f., in a greenhouse. Sixteen impatiens plants were arranged in a square and infested with the same total number of spider mites distributed either evenly (equal numbers on all plants) or clumped (divided equally among the 4 central plants), simulating a “hot spot.” The predatory mite, Phytoseiulus persimilis Athias-Henriot, was released at a 1:4 predator:prey ratio based on total spider mites in the experimental unit, but the pattern of release was either even or clumped, which simulated broadcast or point-release strategies, respectively. Nine days after predator release, spider mite populations were reduced in all treatments, but only in the clumped pest-clumped predator treatment were spider mites undetectable. Poorest pest suppression occurred in the clumped spider mite-even predator treatment. Eighteen days after predator release, spider mites were eliminated in all treatments, but a reduction in average plant damage occurred only in treatments in which the predator release pattern matched the spider mite distribution (i.e., even-even or clumped-clumped) with the greatest reduction in the even-even treatment. Results suggest that there is an advantage to releasing predators in “hot spots” provided that the recommended predator:prey ratio is maintained within infested patches. If more uniform predator releases are planned, overall predator numbers need to be kept sufficiently high so that the predator:prey ratio of 1:4 shown to prevent damage on impatiens is achieved in higher-density spider mite patches.     

Pest response in packed table grapes to low temperature storage combined with slow-release sulfur dioxide pads in basic and large-scale tests

The effect of low temperature storage combined with slow release sulfur dioxide pads was determined in basic laboratory and large-scale commercial tests on western flower thrips, Frankliniella occidentalis Pergande; grape mealybug, Pseudococcus maritimus (Ehrhorn); Pacific spider mite, Tetranychus pacificus McGregor; twospotted spider mite, Tetranychus urticae Koch; and omnivorous leafroller, Platynota stultana Walshingham. Temperatures within the foam containers among the packed clusters decreased from ambient to 2 degrees C within approximately 1 d and ranged from 0.4 to 1.7 degrees C in all tests. Sulfur dioxide concentrations in the foam containers ranged between 0.2 and 1.6 ppm during the 1- to 6-wk storage period in basic tests and 0.5-1.1 ppm during the 1- to 8-wk storage period in the large-scale test. Western flower thrips was completely controlled by a > or =1-wk exposure. Grape mealybug mortality was > or =93% after 2-5 wk exposures and 100% after a 6-wk exposure in basic tests. Pacific spider mite and twospotted spider mite mortality was 98.0 and 99.6%, respectively, after a 6-wk exposure. Mortality of grape mealybug and twospotted spider mite increased significantly at > or =3-wk exposures and Pacific spider mite mortality increased significantly at > or =4-wk exposures. Mortality of the spider mites in general was directly related to the duration of exposure. An 8-wk exposure to low temperature storage combined with slow release sulfur dioxide pads in the large-scale test resulted in 100% mortality of western flower thrips, twospotted spider mite, and omnivorous leafroller. The treatment resulted in <8% survival of grape mealybug and <1% survival of Pacific spider mite in the large-scale test. The combination treatment offers an economical method to attain quarantine control of certain insects and mites.     

Resistance status of the carmine spider mite,Tetranychus cinnabarinus and the twospotted spider mite,Tetranychus urticae to selected acaricides on strawberries

The carmine spider mite, Tetranychus cinnabarinus (Boisduval) and the twospotted spider mite, Tetranychus urticae Koch, are serious pests of strawberries and many other horticultural crops. Control of these pests has been heavily dependent upon chemical acaricides. Objectives of this study were to determine the resistance status of these two pest species to commonly used acaricides on strawberries in a year‐round intensive horticultural production region. LC₉₀ of abamectin for adult carmine spider mites was 4% whereas that for adult twospotted spider mites was 24% of the top label rate. LC_90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 0.5%, 0.5%, 1.4% and 83% of their respective highest label rates for carmine spider mite eggs, 0.7%, 2.7%, 12.1% and 347% of their respective highest label rates for the nymphs. LC_90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 4.6%, 11.1%, 310% and 62% of their respective highest label rates for twospotted spider mite eggs, 3%, 13%, 432,214% and 15% of their respective highest label rates for the nymphs. Our results suggest that T. cinnabarinus have developed resistance to bifenazate and that the T. urticae have developed resistance to hexythiazox. These results strongly emphasize the need to develop resistance management strategies in the region.     

The invasive spider mite Tetranychus evansi (Acari: Tetranychidae) alters community composition and host-plant use of native relatives

The tomato spider mite Tetranychus evansi Baker and Pritchard (Acari: Tetranychidae), is a worldwide pest of solanaceous crops that has recently invaded many parts of the world. In the present study we examined the ecological impact of its arrival in the Mediterranean region. The spider mite and phytoseiid mite assemblages in various crop and non-crop plants in three areas of Valencia (Spain) were studied a few months before and 10 years after the invasion of T. evansi. According to rarefaction analyses, the invasion of T. evansi did not affect neither the total number of species in the mite community examined (spider mite and phytoseiid species) nor the number of species when the two communities were examined separately. However, after the invasion, the absolute and relative abundance of the native Tetranychus species was significantly reduced. Before the invasion, T. urticae and T. turkestani were the most abundant spider mites, accounting for 62.9 and 22.8 % of the specimens. After the invasion, T. evansi became the most abundant species, representing 60 % of the total spider mites recorded, whereas the abundance of T. urticae was significantly reduced (23 %). This reduction took place principally on non-crop plants, where native species were replaced by the invader. Null model analyses provided evidence for competition structuring the spider mite community on non-crop plants after the invasion of T. evansi. Resistance to acaricides, the absence of efficient native natural enemies, manipulation of the plant defenses and the web type produced by T. evansi are discussed as possible causes for the competitive displacement.     

Host plant-induced changes in detoxification enzymes and susceptibility to pesticides in the twospotted spider mite (Acari: Tetranychidae)

Adult female twospotted spider mites, Tetranychus urticae Koch, reared on lima bean plants were moved to cucumber, maize, or new lima bean plants (the latter being a control) and evaluated after 24 h or 7 d for changes in susceptibility to three pesticides and in levels of related detoxification enzymes. The largest and most consistent changes were observed in mites feeding on cucumber. Susceptibility of mites on cucumber to the synthetic pyrethroids bifenthrin and lambda-cyhalothrin was greater than that of mites reared on lima bean and maize after only 24 h on the plants, and remained higher after 7 d. Mites on cucumber also were more susceptible to the organophosphate dimethoate than were mites on lima bean, but only after 7 d on the host. Susceptibility was inversely related to activities of both general esterase and glutathione S-transferase (GST) in mites on cucumber; general esterase and GST activities were 60 and 25% lower, respectively, than activities of twospotted spider mite on lima bean after 7 d of feeding. Mites on maize were slightly but significantly more susceptible than those on lima bean to bifenthrin, but not to lambda-cyhalothrin, after 7 d and to dimethoate after 24 h but not after 7 d. General esterase and GST activities in twospotted spider mite fed on maize for 24 h were 20 and 16% higher, respectively, than activities in twospotted spider mite on lima bean, but general esterase activity was 30% lower than lima bean-fed mites and GST was not different after 7 d. Thus, plant-induced changes in general esterase activity, perhaps in combination with GST activity, in twospotted spider mite appear to be inversely related to, and possibly responsible for, changes in susceptibility of twospotted spider mite to several pesticides, particularly the synthetic pyrethroids. General esterases appear to play less of a role in the detoxification of the organophosphate insecticide dimethoate.     

Introduction ofPhytoseiulus persimilis for twospotted spider mite control in greenhouses in Egypt [Acari: Phytoseiidae,tetranychidae]

The exotic predaceous mite,Phytoseiulus persimilis Athias-Henriot and the 2 native onesPhytoseius finitimus Ribaga andAmblyseius gossipi Elbadry were released on greenhouse cucumber plants in Egypt to examine their efficiency to control the twospotted spider miteTetranychus urticae Koch.P. persimilis proved to be sufficiently effective for the twospotted spider mite control under greenhouse conditions in Egypt. The 2 before-mentioned native predators were lost soon after release in the greenhouse although they are key mite predators on outdoor crops in this area.      

Efficacy and persistence of rosemary oil as an acaricide against twospotted spider mite (Acari: Tetranychidae) on greenhouse tomato

Efficacy of rosemary, Rosmarinus officinalis L., essential oil was assessed against twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), as well as effects on the tomato, Lycopersicum esculatum Mill., host plant and biocontrol agents. Laboratory bioassay results indicated that pure rosemary oil and EcoTrol (a rosemary oil-based pesticide) caused complete mortality of spider mites at concentrations that are not phytotoxic to the host plant. The predatory mite Phytoseiulus persimilis Athias-Henriot is less susceptible to rosemary oil and EcoTrol than twospotted spider mite both in the laboratory and the greenhouse. Rosemary oil repels spider mites and can affect oviposition behavior. Moreover, rosemary oil and rosemary oil-based pesticides are nonpersistent in the environment, and their lethal and sublethal effects fade within 1 or 2 d. EcoTrol is safe to tomato foliage, flowers, and fruit even at double the recommended label rate. A greenhouse trial indicated that a single application of EcoTrol at its recommended label rate could reduce a twospotted spider mite population by 52%. At that rate, EcoTrol did not cause any mortality in P. persimilis nor did it affect their eggs. In general, EcoTrol was found to be a suitable option for small-scale integrated pest management programs for controlling twospotted spider mites on greenhouse tomato plants.     

Within-plant distribution of twospotted spider mites (Acari: Tetranychidae) on impatiens: development of a presence-absence sampling plan

The twospotted spider mite, Tetranychus urticae Koch, is an important pest of impatiens, a floricultural crop of increasing economic importance in the United States. The large amount of foliage on individual impatiens plants, the small size of mites, and their ability to quickly build high populations make a reliable sampling method essential when developing a pest management program. In our study, we were particularly interested in using spider mite counts as a basis for releasing biological control agents. The within-plant distribution of mites was established in greenhouse experiments and these data were used to identify the sampling unit. Leaves were divided into three zones according to location on the plant: inner, intermediate, and other. On average, 40, 33, and 27% of the leaves belonged to the inner, intermediate, and other leaf zones, respectively. However, because 60% of the mites consistently were found on the intermediate leaves, intermediate leaves were chosen as the sampling unit. These results lead to the development of a presence-absence sampling method for T. urticae by using Taylor coefficients generic for this pest. The accuracy of this method was verified against an independent data set. By determining numerical or binomial sample sizes for consistently estimating twospotted spider mite populations, growers will now be able to determine the number of predatory mites that should be released to control twospotted spider mites on impatiens.     

Effects of acclimation and diapause on the thermal tolerance of the two-spotted spider mite Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae, is a worldwide pest species that overwinters as diapausing females. Cold hardening is presumed to start during diapause development to ensure the successful overwintering of this species. To address this hypothesis, we compared cold tolerance between non-diapausing and diapausing females. We measured supercooling point (SCP) and survival to acute cold stress by exposing the mites at a range of sub-zero temperatures (from −4 to −28 °C for 2 h). The mean SCPs of non-diapausing and diapausing females were −19.6±0.5 and −24.7±0.3 °C respectively, and freezing killed the mites. Diapausing females were significantly more cold tolerant than non-diapausing ones, with LT₅₀ of −19.7 and −13.3 °C, respectively. Further, we also examined the effects of cold acclimation (10 d at 0 or 5 °C) in non-diapausing and diapausing females. Our findings indicated that diapause decreased SCP significantly, while cold acclimation had no effect on the SCP except for non-diapausing females that were acclimated at 5 °C. Acclimation at 5 °C enhanced survival to acute cold stress in diapausing and non-diapausing females, with LT₅₀ of −22.0 and −17.1 °C, respectively. Altogether, our results indicate that T. urticae is a chill tolerant species, and that diapause and cold acclimation elevate cold hardiness in this species.     

Purification and partial characterization of vitellin from the eggs of the hard tick,Dermacentor variabilis

The major yolk proteins were purified from the eggs of the hard tick, Dermacentor variabilis using gel filtration and ion exchange chromatography. Two vitellin proteins were identified and designated vitellin A (480 kilodaltons; kDa) and vitellin B (370 kDa). The isolectric points were pH 6.1 and 6.25, respectively. The absorption maxima for both proteins were 280 and 400 nm. The buoyant density of vitellin A was 1.281 g/ml and vitellin B 1.278 g/ml. The vitellins were hemoglycolipoproteins as indicated by selective staining of polyacrylamide gels, carbohydrate analyses and lipid analyses. Under reducing conditions (SDS-PAGE), vitellin A had eight major polypeptides at 135, 110, 98, 80, 67, 50, 45, and 35 kDa. Vitellin B was identical to vitellin A with the addition of a 93 kDa subunit. The only carbohydrate detectable in the proteins was mannose. The neutral lipids detected in both proteins were cholesteryl esters, triglycerides, free fatty acids and their methyl esters, and cholestrol. The only detectable phospholipid in both proteins was phosphatidylethanolamine. The purified vitellins were immunologically identical to female hemolymph proteins but not to host hemoglobin. Antivitellin antibodies to vitellin were used to identify possible locations of vitellogenin in the organs of ovipositing females.     

Genetic differences between two spider crabs Pisoides bidentatus (A. Milne-Edwards, 1873) and Pugettia quadridens (de Haan, 1839) (Decapoda: Brachyura: Majoidea) from the Sea of Japan

Biochemical genetics was applied to elucidate the taxonomic position of the spider crab Pisoides bidentatus. Two morphologically similar spider crabs, P. bidentatus and Pugettia quadridens, were compared with four sympatric brachyuran species, Eriocheir japonicus, Hemigrapsus sanguineus, Hemigrapsus penicillatus (Varunidae), and Cancer amphioetus (Cancridae), using 20 allozyme loci. High genetic identity-value between P. bidentatus and P. quadridens (I = 0.758 ± 0.092) suggests that they should evidently be placed to one genus. This conclusion is supported by the similar identity-value between two species of the genus Hemigrapsus (I = 0.821 ± 0.078) and the low genetic similarity (I = 0.125 ± 0.05) between different genera, Hemigrapsus and Eriocheir, within the family Varunidae.     

Spatial and temporal factors affecting parasite genotypes encountered by hosts: Empirical data from American dog ticks (Dermacentor variabilis) parasitising raccoons (Procyon lotor)

The American dog tick (Dermacentor variabilis) is an important vector of numerous pathogens of humans and animals. In this study, we analysed population genetic patterns in D. variabilis at scales of the host individual (infrapopulation) and population (component population) to elucidate fine-scale spatial and temporal factors influencing transmission dynamics. We genotyped D. variabilis collected from raccoons (Procyon lotor) trapped in two habitat patches (located in Indiana, USA) which were spatially proximate (5.9 km) and limited in size (10.48 Ha and 25.47 Ha, respectively). Despite the fine spatial sampling scale, our analyses revealed significant genetic differentiation amongst component populations and infrapopulations (within each component population), indicating a non-random pattern of encountering tick genotypes by raccoons at both scales evaluated. We found evidence for male-biased dispersal in the ticks themselves (in one component population) and an age-bias in spatial scales at which raccoons encountered ticks in the environment. At the scale of the component population, our analyses revealed that raccoons encountered ticks from a limited number of D. variabilis family groups, likely due to high reproductive variance amongst individual ticks. Finally, we found evidence for a temporal effect with raccoons encountering ticks in the environment as “clumps” of related individuals. While the genetic structure of parasite populations are increasingly being investigated at small spatial scales (e.g. the infrapopulation), our data reveal that genetic structuring can originate at scales below that of the infrapopulation, due to the interaction between temporal and biological factors affecting the encounter of parasites by individual hosts. Ultimately, our data indicate that genetic structure in parasites must be viewed as a consequence of both spatial and temporal variance in host-parasite interactions, which in turn are driven by demographic factors related to both the host and parasite.     

Isolation and characterization of a new Cu-Fe protein from Desulfovibrio aminophilus DSM12254

The isolation and characterization of a new metalloprotein containing Cu and Fe atoms is reported. The as-isolated Cu-Fe protein shows an UV-visible spectrum with absorption bands at 320 nm, 409 nm and 615 nm. Molecular mass of the native protein along with denaturating electrophoresis and mass spectrometry data show that this protein is a multimer consisting of 14 ± 1 subunits of 15254.3 ± 7.6 Da. Mössbauer spectroscopy data of the as-isolated Cu-Fe protein is consistent with the presence of [2Fe-2S]²⁺ centers. Data interpretation of the dithionite reduced protein suggest that the metallic cluster could be constituted by two ferromagnetically coupled [2Fe-2S]⁺ spin delocalized pairs. The biochemical properties of the Cu-Fe protein are similar to the recently reported molybdenum resistance associated protein from Desulfovibrio, D. alaskensis. Furthermore, a BLAST search from the DNA deduced amino acid sequence shows that the Cu-Fe protein has homology with proteins annotated as zinc resistance associated proteins from Desulfovibrio, D. alaskensis, D. vulgaris Hildenborough, D. piger ATCC 29098. These facts suggest a possible role of the Cu-Fe protein in metal tolerance.     

Influence of diet on life table parameters of <Emphasis Type="Italic">Iphiseius degenerans</Emphasis> (Acari: Phytoseiidae)

Studies on the reproduction, longevity and life table parameters of Iphiseius degenerans (Berlese) were carried out under laboratory conditions of 25 ± 1 °C, 75 ± 5% RH and 16L:8D h. As food sources for the predatory mite, Ricinus communis L. pollen, all stages of the spider mite Tetranychus urticae Koch, Frankliniella occidentalis (Pergande) larvae, and Ephestia kuehniella Zeller eggs were selected. All diets were accepted as food by the adult mites. Female longevity ranged from 29.5 to 42.4 days, the highest value was recorded on a diet of Ephestia eggs. The highest percentage of females escaping the experimental arena was observed on the diet consisting of thrips larvae. The highest oviposition rate (1.9 eggs/female.day) was recorded when the predator was fed on spider mites on an artificial substrate. For other diets, oviposition rates ranged from 1.0 to 1.3 eggs/female.day. The intrinsic rate of natural increase (r _m) of I. degenerans varied between 0.015 and 0.142 females/female.day. The diet consisting of castor bean pollen resulted in the highest population growth whereas the diet on spider mites brushed off onto a bean leaf arena resulted in the slowest population growth. This can be explained by the inability of the predator to cope with the webbing of T. urticae, and the high escape rate of the progeny when reared on spider mites. The percentage of females in the offspring ranged from 40 to 73%.This revised version was published online in May 2005 with a corrected cover date.     

Effects of Temperature and Relative Humidity on Development,Reproduction, and Predation in Feltiella acarisuga (Vallot) (Diptera: Cecidomyiidae)

The predatory gall midge Feltiella acarisuga (Vallot) (Diptera: Cecidomyiidae) is a biological control agent for twospotted spider mites on greenhouse vegetable crops. Effects of temperature and relative humidity (RH) on development of immatures, reproduction, and prey capture were determined in order to confirm the suitability of F. acarisuga for use in greenhouses. Developmental time ranged from 10 days at 27°C to 34 days at 15°C. At 20°C, developmental time was significantly shorter at 96% RH than at 84% RH. There was very poor survival of immatures at 64% RH and none at 36%. Lifespan of adult females decreased with increasing temperature, but temperature had no significant effect on number of eggs laid. At 20°C, lifespan was longer at 84 and 96% RH than at 64 or 36% RH. The number of spider mites attacked by 3-day-old larvae over 8 h increased with increasing temperature from 15 to 27°C. The number of mites attacked also increased with increasing RH at 27°C. We conclude that F. acarisuga will complete its life cycle and reproduce under conditions typically found in vegetable greenhouses in northern temperate climates. However, extended periods of low RH (<60% RH) could reduce reproduction and survivorship sufficiently to impair the predator's action against spider mite populations.