Autumnal emergence of Anagrus wasps,egg parasitoids of Empoasca vitis,from grapevine leaves and their migration towards brambles

• 1 The Anagrus‘atomus’ parasitoid group (Hymenoptera: Mymaridae), associated with Empoasca vitis (Göthe) (Homoptera: Cicadellidae), overwinters on vegetation surrounding vineyards. The emergence of parasitoid adults from grapevine leaves in autumn was studied in north‐eastern Italy, both in relation to the E. vitis egg‐laying period and to the presence of leafhoppers overwintering as eggs on Rubus bushes.
• 2 Autumnal peaks of Anagrus captured using yellow sticky traps were observed first on grapevines and then on brambles. Parasitoid captures in vineyards were observed for more than 1 month after the last first‐instar nymphs of the grape leafhoppers were noticed. Two species belonging to the A. ‘atomus’ group, Anagrus atomus and Anagrus ustulatus, were captured both on grapevines and brambles.
• 3 Parasitoids of the A.‘atomus’ group can emerge from third‐generation grape leafhopper eggs in accordance with two different development time patterns (i.e. normal or delayed). Individuals with delayed emergence required up to 2.2‐fold more time to develop from an egg to adult than individuals with normal emergence. This meant that some parasitoid adults emerged in autumn from eggs of grape leafhopper laid in August.
• 4 A delayed emergence as a result of a slower development ensures that the A.‘atomus’ parasitoid group is synchronized with the egg‐laying of leafhoppers that overwinter as eggs on Rubus spp.
• 5 Consequently, leafhoppers overwintering as eggs on brambles play a key role in the ecology of the relationship between grape leafhoppers and the A.‘atomus’ parasitoid group.

     

Influence of grapevine cultivars on the leafhopper <Emphasis Type="Italic">Empoasca vitis</Emphasis> and its egg parasitoids

The leafhopper Empoasca vitis (Göthe) (Homoptera: Cicadellidae) can cause economic damage in European vineyards. Egg parasitoids, in particular Anagrus atomus (Linnaeus) (Hymenoptera: Mymaridae), are the most important natural enemies of the leafhopper. In four different years, leaves of ten grapevine cultivars, which were grown in a vineyard of north-eastern Italy, were collected at the end of the leafhopper 2nd generation to determine the total number of E. vitis eggs per leaf and the percentage of the E. vitis eggs parasitized. These data were analysed for correlation with leaf density and foliar pubescence. The E. vitis eggs per leaf and the percentage of eggs parasitized by Anagrus spp. were significantly influenced by the cultivar. The number of E. vitis eggs per leaf was positively correlated to leaf density, but it was not influenced by leaf hair density. The parasitization rate by Anagrus spp. was affected by foliar pubescence, especially by erect hairs on the veins. These findings could be used for integrated pest management. In particular, (1) the more susceptible cultivars can be used as early indicators of leafhopper infestation, (2) agronomic practices, that reduce leaf density, could decrease the E. vitis population level and (3) clones with glabrous leaves would favour egg parasitoid activity.     

Searching and Oviposition Behavior of Anagrus atomus L. (Hymenoptera: Mymaridae) on Four Host Plants of Its Host, the Green Leafhopper Empoasca decipiens Paoli (Homoptera: Cicadellidae)

Anagrus atomus L. is an important egg parasitoid of the green leafhopper Empoasca decipiens Paoli. In this study the ability of the parasitoid to locate and parasitize its host was investigated on four host plants, i.e., broad beans (Vicia faba L.), sweet pepper (Capsicum annuum L.), cucumber (Cucumis sativus L.), and French beans (Phaseolus vulgaris L.). For each plant species, the behavior of the parasitoid was observed on E. decipiens infested and noninfested plants. Searching and oviposition behavior were characterized by drumming, probing, and resting. Parasitoids spent significantly less time on non-infested than infested plants, 274.5 and 875.7 s, respectively, and no probing behavior was observed on non-infested plants. Frequency of resting behavior was significantly greater on non-infested than on infested plants. Total foraging time was significantly longer on infested than on non-infested plants, indicating that A. atomus females can efficiently discriminate between leaves with and without infestation. Parasitism of A. atomus was influenced by parasitoid density, with the highest parasitism rate (64.0%) obtained at a density of 10 A. atomus females/0.1356 m² but the number of parasitized eggs per female and the searching efficiency decreased with increasing parasitoid density.     

Seasonal Migration of Apolygus spinolae (Hemiptera: Miridae) between Grapevines and Herbaceous Plants

This study was conducted to verify the seasonal migration of Apolygus spinolae (Meyer-Dür) between grapevines and herbaceous plants. Overwintering eggs were hidden in the hair layer under grapevine bud scales. A. spinolae adults were captured on sticky traps in the grapevine yard from late spring to early summer, dwindled through the summer, and captured again in late fall. However, adults were observed from early summer in herbaceous plant fields. A. spinolae adults were abundant during the summer of July and August in the herbaceous field, and thereafter its density decreased through fall. A few or no A. spinolae was found on mesh-netted grapevines after the installation year of the mesh-net, which indicated that A. spinolae adults migrating to lay overwintering eggs during the autumn could not land at the grapevines because of the mesh-net. Damaged shoots by A. spinolae were concentrated near the edge of grapevine yards bordering the herbaceous plants. This distribution pattern of shoot damage was believed to be related to an oviposition behavior of A spinolae, reflecting that adults migrating from herbaceous plants lay eggs more frequently in grapevines adjacent to the summer host plants. Seasonal occurrence of A. spinolae in grapevine yards was suggested as follows: A. spinolae overwinter as eggs in dormant buds on grapevines and hatch in the spring. Nymphs feed on grapevines then develop to adults (spring population), and migrate to herbaceous plants. A. spimolae spends the summer on the herbaceous hosts (summer population). Then, adults migrate back to grapevines in late autumn and lay overwintering eggs.     

Mite populations on grapevines in south-eastern Australia: Implications for biological control of grapevine mites (Acarina: Tenuipalpidae,Eriophyidae)

Pest and predatory mite populations were monitored over a 2 year period on grapevines in three viticultural regions of southern Australia (The Riverlands, Sunraysia and Murrumbidgee Irrigation Area [MIA]). The mite pestsBrevipalpus spp..Colomerus vitis (Pagenstecher) andCalepitrimerus vitis (Nalepa) occurred in each region with a predatory mite fauna which showed considerable interregional variation in incidence, abundance and composition. Nine species of Phytoseiidae, the dominant predatory mite family, were recorded inhabiting grapevines. In the Riverlands, mite populations were apparently suppressed by two phytoseiids (Typhlodromus doreenae Schicha,Amblyseius victoriensis (Womersley)) in vineyards on which no insecticide was used and on which sulphur and copper were used to control vine diseases. In Sunraysia and MIA, vineyards which generally had greater inputs of synthetic pesticides, particularly fungicides, five to eight phytoseiid species were recorded. However, they were less abundant and appeared to have less impact on mite (particularlyBrevipalpus spp.) populations. The population dynamics of pest and predatory mites on grapevines in southern Australia and implications for mite management based on biological control are discussed with respect to pesticide (particularly fungicide) inputs and phytoseiid biology/ecology.     

Larval development of Empoasca vitis and Edwardsiana rosae (Homoptera: Cicadellidae) at different temperatures on grapevine leaves

The grape leafhopper Empoasca vitis (Homoptera: Cicadellidae) is regarded as a major insect pest in many European grapevine growing areas, with an increasing importance realized in recent years maybe as a result of climatic change. Both larvae and adults feed on the phloem vessels of the leaves, causing characteristic symptoms also referred to as hopperburn. Phenology of adult leafhoppers was monitored in one vineyard in three successive years and indicated that immigration of a few hibernated E. vitis individuals into vineyards might take place already quite early in the year depending on winter temperatures and starts to progress in substantial numbers right at grapevine bud burst. In addition, these monitoring studies have shown that there are several other leafhopper species occurring on grapevine plants besides E. vitis, such as the rose leafhopper Edwardsiana rosae (Homoptera: Cicadellidae). Here, we report on the development of larval instars of both leafhopper species, E. vitis and E. rosae on grapevine leaves under different temperature regimes in the laboratory. Shortest larval developmental time was observed at night temperatures of 13–15°C and day temperatures of 23–25°C, which was in agreement with predicted optimal temperatures for both species. At the temperature regime of 20°C night and 30°C day temperature, either no egg hatch was observed or early development of first‐instar larvae was not successful for both species. These results suggest that warm (18°C) nights and moderately warm (28°C) days are representing the upper thermal threshold for development of both E. vitis and E. rosae embryonic stages on grapevine leaves, questioning current assumptions of an increasing importance of E. vitis as a grapevine pest under future climate change.     

The dynamics of grape leafhopper Empoasca vitis Göthe populations in southern Switzerland and the implications for habitat management

The life cycle of Empoasca vitis and its most important parasitoid Anagrus atomus in southern Switzerland can be divided into three phases. In phase I the adults of E. vitis move from overwintering sites, i.e. primarily conifers, over deciduous plants into the vineyards. The parasitoid A. atomus on the other hand, appears to overwinter in leafhopper eggs, mainly on roses and blackberries. It subsequently completes one generation in leafhopper eggs primarily on blackberries and hazelnuts, before it attacks E. vitis eggs in the vineyards. For phase II, a population model with time‐varying age structures and stochastic properties was constructed for E. vitis. For this purpose a time‐varying distributed delay model with attrition was constructed. Given the calibrated initial density of overwintering females, the model predicts an unacceptable number of E. vitis for the growing season. However, if egg parasitism of A. atomus and Stethynium triclavatum is introduced into the model as an external variable E. vitis densities are predicted which are economically irrelevant. Inphase III E. vitis adults leave the vineyards for the overwintering sites. The model shows the importance of the parasitoid A. atomus during phase II. A. atomus should be favoured by surrounding the vineyards with host plants carrying leafhoppers’ eggs. Consequently, habitat management measures for E. vitis control could be applied to the surroundings of the vineyards.     

Biology of Anagrus atomus (Hymenoptera: Mymaridae), an egg parasitoid of the grape leafhopper Arboridia kermanshah (Homoptera: Cicadellidae)

Biology, morphology and oviposition behavior of Anagrus atomus (Linnaeus), an egg parasitoid of the grape leafhopper Arboridia kermanshah Dlabola in Isfahan, Iran, were investigated. Adults were smaller than those so far reported from other regions. Females continuously drummed on plant surfaces with their antennae to search for host eggs. Parasitoid eggs hatched 2–3 days after oviposition, and A. atomus had two larval instars. First instar larvae were sacciform and immobile. Second instar larvae appeared 4 days after oviposition and were very active, and doubled their body length. The prepupal and pupal stages lasted for 1 and 5–6 days, respectively. Adult emergence began 16 days after oviposition, and peaked on day 17.     

Predicting early spring emergence and late season overwintering movement of Calepitrimerus vitis (Nalepa) (Acari: Eriophyidae) in grapevine

The grape rust mite, Calepitrimerus vitis (Nalepa), is an important grapevine pest worldwide. During the period of early spring emergence and movement to the overwintering refuge in the late season, growers need to control C. vitis properly. We developed forecasting models of early spring emergence and late summer overwintering movement of C. vitis in vineyards for control time. Their activation in the early spring was estimated by changes in density between upper bud and the whole bud. The density of C. vitis on buds was estimated using a washing out method. The proportion of C. vitis on the upper bud was increased as accumulated degree-day (DD) was increased. This relationship was well described by a linear regression model. Based on the model, 153 DD with a base temperature of 10.51?°C, at which emergence rate of C. vitis deutogynes was 70%, was proposed as the control time for C. vitis. Movement of deutogynes in the late summer was observed. The ratio of C. vitis movement for hibernation was increased as the relative night length was getting longer. This relationship was well described by a two-parameter Weibull function. Proportion of migrant deutogynes was low in August. It increased sharply when relative night length was 0.499 (11.97?h, middle September). Therefore, control should be conducted before autumnal equinox in late summer at the latest.     

Life-table study of Anagrus atomus, an egg parasitoid of the green leafhopper Empoasca decipiens, at four different temperatures

The objective of our study was to assess thepotential of the egg parasitoid Anagrusatomus L. (Hymenoptera: Mymaridae) for controlof the greenhouse leafhopper Empoascadecipiens Paoli (Homoptera: Cicadellidae). Theegg-adult development time, survivorship andreproduction of A. atomus were evaluatedat four constant temperatures (16, 20, 24 and28°C). Developmental time ranged from33.6 days at 16°C to 13.3 days at 28°C. Based on a linear regression ofdevelopment rate on temperature the lowerthreshold was estimated at 8.39°C. Anagrus atomus required 263.2 degree-days tocomplete its development from egg to adult. Theegg-adult survival rate and the sex ratio weresignificantly lower at 28°C than at theother three temperatures tested. The intrinsicrate of increase (r _m) variedsignificantly between all four temperatures.The potential of A. atomus to attackdifferent host ages was additionallyinvestigated. Host eggs were parasitizedthroughout their development but rate ofparasitism was reduced in host eggs older thansix days. The number of eggs parasitized waspositively density dependent but the rate ofparasitism decreased with increasing hostdensity. A maximum rate of parasitism of 62.5%was recorded. The potential impact of the eggparasitoid on the population dynamics of E. decipiens is discussed.     

In vitro rearing of Ooencyrtus nezarae (Hymenoptera: Encyrtidae), an egg parasitoid of Riptortus pedestris (Hemiptera: Alydidae)

Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) is a polyphagous egg parasitoid of various true bugs, including Riptortus pedestris (Fabricius) (Hemiptera: Alydidae), a major pest of soybean and fruit trees in northeastern Asia. This study was conducted to develop artificial host eggs containing insect haemolymph for mass rearing of O. nezarae. The haemolymph of Chinese oak silkworm (Antheraea pernyi Guérin-Méneville) pupae was found to be most suitable for artificial eggs for the complete development of O. nezarae. Among 764 parasitoid eggs laid in artificial eggs, 49.2% successfully developed to adult parasitoids. The developmental time in artificial eggs was delayed by 3–5 days relative to that observed in natural host eggs; however there was no significant difference in the length of hind tibia between adults that emerged from artificial and natural host eggs. Moreover, new generations that emerged from artificial eggs reproduced on all egg types offered (either natural or artificial eggs). We propose that the artificial eggs developed herein can therefore be an effective means for mass rearing O. nezarae.     

Habitat diversification tactic for improving biological control: parasitism of the western grape leafhopper

In a previous study we demonstrated greater abundance of the parasitoid Anagrus epos (Girault) in grape vineyards located downwind of prune trees that function as overwintering habitats. This study examines whether these higher A. epos numbers translated into higher egg parasitism rates of the grape leafhopper, Erythroneura elegantula (Osborn). Paired commercial wine-grape vineyard plots, one with and one without adjacent prune trees, were studied within a complete block design in northern and central California. A. epos was the key mortality factor affecting E. elegantula eggs. Point estimates of A. epos parasitism rates were significantly greater in vineyards associated with prune trees during the first E. elegantula generation in both 1991 and 1992. No consistent differences in parasitism rates were observed during the second or third generations. The results indicated that prune trees enhance early season parasitism rates. Cumulative estimates of egg parasitism across E. elegantula generations demonstrated that enhanced early-season parasitism resulted in a net season-long increase in the degree of mortality imposed by A. epos on E. elegantula eggs. Two factors were found to influence parasitism rates: the abundance of early-season A. epos adults moving into vineyards and the density of E. elegantula eggs in vineyards. Our results indicate that diversification of vineyards using prune trees supports overwintering populations of a specialist parasitoid and thereby alters host-parasitoid interactions to favor enhanced parasitism in vineyards.     

Breeding biology of Tenagomysis tasmaniae Fenton,Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton from south-eastern Tasmania (Crustacea: Mysidacea)

The number, size and developmental stage of young in the brood pouch of female Tenagomysis tasmaniae, Anisomysis mixta australis and Paramesopodopsis rufa was recorded throughout the year. Breeding was intensive from spring till the end of autumn for the three species. Calculation of the egg ratio for each species showed that their major reproductive peaks occurred during spring and summer. A winter depression in the breeding cycle was observed for T. tasmaniae and P. rufa, but A. mixta australis ceased breeding during winter. Seasonal variation in the length of gravid females and number of young carried was evident for these three species. Females were longer in spring and summer and carried more young than in autumn and winter. A linear relationship between female length and brood size was demonstrated for each species; annual and seasonal equations were calculated for females carrying each developmental stage. The seasonal equations showed that for a female of given length fecundity was greater during spring than any other season. Natality was estimated to be highest during late spring, summer and early autumn for the three species. No seasonal variation in the size of eggs was evident for the three species. The reproduction pattern of T. tasmaniae, A. mixta australis and P. rufa appears to be very similar to that reported for the majority of iteroparous coastal temperate mysids throughout the world.     

Occurrence and distribution of the grape rust mite Calepitrimerus vitis (Nalepa, 1905) in Korea

The grape rust mite, Calepitrimerus vitis, was identified from grapevines firstly in Korea. In the spring of 2011, symptoms characterized by the retarded growth of young shoots and flower buds in the grapevine were reported by local farmers in Hwaseong, Gyeonggi province of Korea. A large number of the small, white, and longitudinal mites were observed both on the twig surfaces and the overwintering buds. The mite was identified as Calepitrimerus vitis (Nalepa) (Acari: Eriophyidae) by morphological observations under both a microscope and scanning electron microscope (SEM). Nationwide surveys in 2011–2012 were conducted to figure out the distribution of the mite, revealing that the mite was widely distributed in the grape production area in Korea both in greenhouse and in open field vineyards. Interestingly, the mite density was much higher in Hwaseong, a middle-west coast of Korea, with several hundred mites per overwintering bud. However, no significant damage was observed from the sprouting season to the harvest time, except for the retarded growth of shoot and flower buds in the early season. The morphological characteristics of C. vitis with SEM micrographs and the survey results in major grape production areas in Korea are reported herein.     

Effects of seasonal variation in host quality and availability on parasitism by the egg parasitoid Telenomus coloradensis

Hemlock looper, Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae), is one of the most important defoliator in North American forests. The common egg parasitoid Telenomus coloradensis Crawford (Hymenoptera: Platygastridae) plays a significant role as a natural control agent, with parasitism levels in spring typically higher than in fall. The objectives of this study were to quantify changes in host acceptance and reproductive performance of the parasitoid in relation to (1) host egg fertilization in fall, (2) host diapause status, (3) host embryonic development in spring, and (4) host deprivation during summer. Our results indicate that T. coloradensis do not have the capacity to develop in unfertilized host eggs, whereas early‐diapausing eggs are more suitable for the parasitoid than post‐diapausing eggs. Furthermore, the host physiological suitability decreases with embryonic development in spring. Finally, a host deprivation period during the summer tends to negatively affect the parasitic activity of T. coloradensis. These laboratory results confirm previous hypotheses concerning T. coloradensis seasonal ecology and contribute to a better understanding of the effect of hemlock looper egg physiology and availability on the reproductive potential of T. coloradensis.     

Factors affecting the bionomics of the eastern African egg parasitoid Trichogramma bournieri Pintureau & Babault (Hymenoptera: Trichogrammatidae)

The trichogrammatid Trichogramma bournieri Pintureau & Babault is a polyphagous parasitoid of eggs of several cereal stemborer species in eastern Africa. The effects of host species, host age and duration of host deprivation on the performance of the parasitoid were studied in the laboratory. Host acceptance and suitability were tested using five stemborer species. The noctuids Sesamia calamistis Hampson, Sesamia nonagrioides (Lefebvre), Busseola fusca (Fuller) the crambid Chilo partellus (Swinhoe) and the pyralid Eldana saccharina Walker were successfully parasitized by T. bournieri. Parasitism, number of progeny and developmental time varied significantly with host species. The eggs of S. calamistis and B. fusca were the most suitable, whereas those of E. saccharina were the least suitable. While parasitism and number of progeny tended to decrease with age of hosts, there were no significant differences in sex ratio. Longevity of the parasitoid increased with increase in deprivation of hosts from 0 to 12 days. Average lifetime fecundity per female decreased, indicating resorption of eggs.     

Population dynamics and seasonal variation in the embryonic dormancy of Pilophorus gallicus (Hemiptera: Miridae): ‘don't put all your eggs in one basket'

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Resting stages in the life cycle of Eudiaptomus graciloides (Lill.) (Copepoda: Calanoida) in Lake Glubokoe

Seasonal changes in the abundance, age composition, vertical distribution, lipid and protein body content, development rates in the older copepodids (CIV and CV) and reproduction characteristics were studied in Eudiaptomus graciloides in the mesotrophic Lake Glubokoe (Moscow) region). Two periods of reproduction were observed: spring and late summer/autumn. The older copepodids, having accumulated lipid reserves during phytoplankton bloom, descended into the meta- and hypolimnion at the beginning of the summer. These copepods did not feed, but instead consumed their lipid reserves. A considerable delay in development (up to 40-60 days) of CIVs and CVs was found. The descended CIVs and CVs incubated under ambient temperature developed 4-5 times slower than their surface counterparts, while temperature dependence could only account for a 2-fold slow down. The descended copepods are believed to form a summer resting stock. In October, females began to produce resting eggs. The period of switching from subitaneous to resting egg production was very brief, not longer than 2-3 weeks. The percentage of subitaneous eggs produced in mid-October tended to increase when females were exposed to an increased photoperiod. At the beginning of February, latent eggs kept in a cooling container in the darkness started hatching. This process could be speeded up under natural photoperiod and increased temperature. The over-wintering population consisted largely of adults. Thus, E.graciloides includes three types of diapause in the life cycle: resting eggs, summer resting stage at CIV-CV, and overwintering adults.      

Exposure of <Emphasis Type="Italic">Eocanthecona furcellata</Emphasis> (Hemiptera: Pentatomidae) nymphs and adults to high temperatures induces an aestivo-hibernal egg diapause: a strategy for surviving hot summers

The predatory stink bug Eocanthecona furcellata (Wolff) (Hemiptera: Pentatomidae), which is widely distributed in the subtropics and tropics, is a potential biological control agent for lepidopteran, coleopteran, and hemipteran pests. We investigated development of eggs oviposited by E. furcellata females subjected to various photoperiods (i.e., 8L:16D, 12L:12D, and 16L:8D) and temperature regimes (i.e., 26:26, 30:28, 32:30, 34:32, 35:33, and 36:34 °C; temperatures at light and dark phases, respectively) at different developmental stages. Exposure of E. furcellata nymphs and adults to different photoperiods and temperature regimes affected the development of eggs they subsequently oviposited. Temperatures greater than 30 °C induced diapause in a portion of the eggs, as evidenced by the delayed appearance of the black circle and the red spot, characteristics of early and late stage of embryonic development, respectively. The proportion of diapausing eggs generally increased with increasing temperature exposure, whereas it decreased with advancing developmental stage/age at which E. furcellata was subjected to the temperature regime. Although viability of diapausing eggs was lower than that of non-diapausing eggs, diapausing eggs survived longer under high temperatures. The trade-off between survivability and viability may be a strategy to survive unpredictability of summer temperatures.     

Production of Anagrus epos Girault (Hymenoptera: Mymaridae) on Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) eggs

Anagrus epos Girault (Hymenoptera: Mymaridae) is a natural enemy candidate for a classical biological control program targeting the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), in California. Little is known about the biology or ecology of A. epos when it utilizes GWSS eggs as a host. Here, we report the results of laboratory studies that describe the host age preference for oviposition, longevity of A. epos adults provided with different food sources, and developmental rates at six different constant temperature regimes. Anagrus epos is a gregarious parasitoid in GWSS eggs with up to 14 adults emerging from each GWSS egg. In choice and no-choice tests for oviposition, A. epos females successfully parasitized all developmental ages of GWSS eggs (1–8 days old). In choice tests, parasitism rates were significantly higher in 1-, 3-, 4-, and 5-day-old GWSS eggs than in 2-, 6-, 7-, and 8-day-old eggs. If provided with honey and water, honey only, water only, or no food or water, A. epos females lived on average 8.2, 4.7, 2.6, and 1.6 days, respectively. Anagrus epos required 294.1 degree-days above a lower temperature threshold of 12.4 °C to develop from egg to adult (eclosion). Our results provide baseline information useful in the development of an efficient parasitoid mass rearing program for A. epos release and evaluation in California.