Leafhopper Eggs Research Articles

Temporal resource continuity for egg parasitoids of Dalbulus maidis (Hemiptera: Cicadellidae) during winter on irrigated maize crops and edge grasses.

Little is known about winter-season parasitism of eggs of the corn leafhopper Dalbulus maidis DeLong (Hemiptera: Cicadellidae), an important pest of maize throughout the Americas. Our study, conducted in Mexico, aimed to characterize winter-season parasitism of corn leafhopper eggs on maize crops cultivated with drip irrigation and on wild grasses that grow on the edges of maize crops when maize is not present. Maize leaves baited with D. maidis eggs were used to trap the egg parasitoids in the field. In the first year (2022), parasitism of D. maidis eggs was investigated in maize fields planted contiguously on different dates (asynchronous planting). In the second year (2023), parasitism of D. maidis eggs was evaluated in edge grasses and in adjacent maize crops planted on the same date (synchronous). The highest percentage of parasitism (53%), percentage of emergence, and total abundance of egg parasitoids were found in asynchronous maize fields. Here, Anagrus virlai Triapitsyn (Hymenoptera: Mymaridae), Paracentrobia subflava (Girault) (Hymenoptera: Trichogrammatidae), and Pseudoligosita sp. (Hymenoptera: Trichogrammatidae) wasps were found parasitizing the D. maidis eggs, with P. subflava being the most abundant. In wild edge grasses, only P. subflava was found, showing low levels of parasitism, while in synchronous maize, P. subflava increased its percentage of parasitism (up to 37%), percentage of emergence, and abundance, during winter. These results suggest that P. subflava acts as an efficient biological control agent of D. maidis in irrigation-grown maize crops during the winter season, and that edge grasses are overwinter habitats for P. subflava.

Does weed infestation alter the population density of harmful leafhopper species in second crop maize?

Weed-insect interaction has been studied for decades to determine the role of weeds in insect infestation. This study investigated the impact of weed density on the population density of important leafhopper species (Cicadellidae: Hemiptera) and their egg parasitoid Anagrus atomus (L.) (Hymenoptera: Chalcidoidea) in maize (Zea mays L.) planted as second crop in Şanlıurfa province, Türkiye during 2022 and 2023. Population densities of harmful leafhopper species, i.e., Zyginidia sohrab (Zachvatkin), Empoasca decipiens (Paoli), Asymmetrasca decedens (Paoli), Psammotettix striatus (Linnaeus), and their parasitoid, i.e. A. atomus were monitored by yellow sticky traps (RAL-1016) under weedy and weed-free conditions. Three traps were hung in each experimental unit and the densities of target species were recorded weekly. The population densities of leafhopper species feeding on Sorghum halepense (L.) (Johnsongrass) and the effect of A. atomus on their population density were also determined in weedy treatment. A total 15 maize leaves were taken from both weedy and weed-free treatments, and S. halepense leaf tissues containing leafhopper eggs parasitized by A. atomus were counted weekly. Weed density had non-significant effect on the population density of Z. sohrab during both years. Contrastingly, increasing weed density increased the population density of E. decipiens & A. decedens complex in 2022. Nevertheless, weed density had non-significant effect on the population density of E. decipiens & A. decedens complex during 2023. Weedy treatment recorded higher population density of P. striatus (140 and 100 adults, respectively); however, both weedy and weed-free treatments recorded similar density (125 and 97 adults) during 2023. Weed density proved a significant factor in increasing A. atomus density. A total of 2935 parasitized eggs were recorded from the weedy treatment, whereas 1609 parasitized eggs were recorded from weed-free treatment. Although direct relationship between leafhoppers and weed density remains uncertain, integrated pest management strategies must consider phytophagous insects feeding on weeds at field edges and within fields and the natural enemy complex.

Evaluation of a low-cost staining method for improved visualization of sweet potato whitefly (Bemisia tabaci) eggs on multiple crop plant species

BackgroundThe sweet potato whitefly (Bemisia tabaci) is a globally important insect pest that damages crops through direct feeding and by transmitting viruses. Current B. tabaci management revolves around the use of insecticides, which are economically and environmentally costly. Host plant resistance is a sustainable option to reduce the impact of whiteflies, but progress in deploying resistance in crops has been slow. A major obstacle is the high cost and low throughput of screening plants for B. tabaci resistance. Oviposition rate is a popular metric for host plant resistance to B. tabaci because it does not require tracking insect development through the entire life cycle, but accurate quantification is still limited by difficulties in observing B. tabaci eggs, which are microscopic and translucent. The goal of our study was to improve quantification of B. tabaci eggs on several important crop species: cassava, cowpea, melon, sweet potato and tomato.ResultsWe tested a selective staining process originally developed for leafhopper eggs: submerging the leaves in McBryde’s stain (acetic acid, ethanol, 0.2% aqueous acid Fuchsin, water; 20:19:2:1) for three days, followed by clearing under heat and pressure for 15 min in clearing solution (LGW; lactic acid, glycerol, water; 17:20:23). With a less experienced individual counting the eggs, B. tabaci egg counts increased after staining across all five crops. With a more experienced counter, egg counts increased after staining on melons, tomatoes, and cowpeas. For all five crops, there was significantly greater agreement on egg counts across the two counting individuals after the staining process. The staining method worked particularly well on melon, where egg counts universally increased after staining for both counting individuals.ConclusionsSelective staining aids visualization of B. tabaci eggs across multiple crop plants, particularly species where leaf morphological features obscure eggs, such as melons and tomatoes. This method is broadly applicable to research questions requiring accurate quantification of B. tabaci eggs, including phenotyping for B. tabaci resistance.

Influence of Vineyard Inter-Row Management on Grapevine Leafhoppers and Their Natural Enemies.

Inter-row management in vineyards can influence the abundance of grapevine pests and their natural enemies. In 2013-2015, in a vineyard in northeastern Italy, the influence of two vineyard inter-row management strategies (i.e., alternate mowing, AM, and periodical tillage, PT) on the population dynamics of grapevine leafhoppers Hebata vitis and Zygina rhamni and their natural enemies, the mymarid Anagrus atomus and spiders (Araneae), and other hymenopteran parasitoids, were studied with different survey approaches. The infestations of both leafhoppers were lower in AM than PT due to the reduced leafhopper oviposition and higher nymph mortality in AM. This occurred although leafhopper egg parasitization by A. atomus was greater in PT than AM according to a density-dependent relationship with the leafhopper egg amount. Hymenopteran parasitoids other than A. atomus were the most abundant in AM, probably due to the higher availability of nectar and pollen than in PM. The significantly higher population densities of hunting spiders in AM than PT can be associated with the higher predation of leafhopper nymphs. Therefore, the study demonstrated that the alternate mowing of vineyard inter-rows enhances the abundance of natural enemies, such as spiders and hymenopteran parasitoids, and can contribute to grapevine leafhopper pest control.

Fairyfly egg parasitoids (Hymenoptera: Mymaridae) of the invasive lace bug Corythucha marmorata (Uhler) (Hemiptera: Tingidae) in Japan

The fairyfly Anagrus (Anagrus) virginiae Triapitsyn and Puttler (Hymenoptera: Mymaridae) is identified as a principal egg parasitoid of the chrysanthemum lace bug Corythucha marmorata (Uhler) (Hemiptera: Tingidae) in Japan on Solidago altissima L., Solidago sp., and Bidens pilosa L. (Asteraceae), and on sweet potato, Ipomoea batatas (L.) Lamarck (Convolvulaceae). Both C. marmorata and Solidago spp. as well as Bidens pilosa are invasive in Japan, so it is very likely that A. virginiae was unintentionally introduced and established in the country either with or after the introduction of its insect host. Both sexes of A. virginiae are redescribed and illustrated with digital images based on Japanese specimens to facilitate their recognition, and an updated key to females of Anagrus Haliday species in Japan is given to include A. virginiae and the recently recorded leafhopper egg parasitoid A. (Anagrus) turpanicus Triapitsyn and Hu. In Japan, C. marmorata is a pest of eggplant, Solanum melongena L. (Solanaceae), pepino or sweet cucumber, Solanum muricatum Aiton, sweet potato, and other crops, so potential for classical biological control against this lace bug is discussed. One male specimen of another fairyfly, Erythmelus (Parallelaptera) sp., was also reared from an egg of C. marmorata, the first such record from this lace bug host.

Laboratory study of the effectiveness of confider in controlling leaf-hoppers on a crop of cowpea

Cowpea leafhopper Amrasca biguttula is one of the important pests that afflict the cowpea crop in Iraq and cause economic losses. Therefore, chemical control was studied in the laboratory and its effectiveness in control was demonstrated, as a pesticide was used imidacloprid ;Confider of the Neonicotinoid schemical group Confider concentration was used for spray treatment 25ml/L,50,75,100ml/l. The concentration used for soil treatment is 100g/ml,200,300 ,400g/ml. The results were the treatment of the lowest hatching rate was obtained in leafhopper eggs for spray treatment when using a concentration of 100ml (reached 79.44%), observed that the average of mortality rate resulting from the use of a the pesticide Confider reached to (33.47%) , It is noted that the highest mortality rate was achieved after the passage of time 72 hours of treatment and reached (39.73%).

Interactions between Rice Resistance to Planthoppers and Honeydew-Related Egg Parasitism under Varying Levels of Nitrogenous Fertilizer.

Simple SummaryPlanthopper outbreaks in rice are associated with excessive fertilizer applications. Public research has focused on developing resistant rice to combat these outbreaks. However, to preserve ecosystem resilience, natural enemy efficacy should be maintained on resistant and susceptible rice. We examined the impact of egg parasitoids on planthoppers (Nilaparvata lugens (Stål) [BPH] and Sogatella furcifera (Horváth) [WBPH]) and a leafhopper (Nephotettix virescens (Distant) [GLH]) in field plots of resistant (IR62) and susceptible (IR64) rice under low and high nitrogen. GLH and WBPH were more abundant in low-nitrogen plots during dry (GLH) and wet (GLH, WBPH) season sampling at an early crop stage. GLH were also more abundant on IR64. Parasitoids killed between 24 and 52% of planthopper eggs during exposures in trap plants. Parasitism by Oligosita and Anagrus wasps was higher on IR64 (BPH eggs) and in high-nitrogen plots (Oligosita spp. on BPH and WBPH eggs; Anagrus spp. on BPH eggs). Parasitism by Anagrus spp. was associated with the presence of honeydew and was highest where honeydew was derived from BPH feeding on IR62; these effects were only observed under high nitrogen. Results suggest that honeydew from IR62 favors parasitoids when plants are most vulnerable (i.e., under high nitrogen), thereby countering nitrogen-induced declines in host resistance.Host plant resistance is the most researched method for the management of planthoppers and leafhoppers in tropical rice. For optimal effects, resistance should be resilient to fertilizer inputs and work in synergy with natural enemies. In field plot experiments, we examined how rice resistance and fertilizer inputs affect mortality of planthopper and leafhopper eggs by hymenopteran parasitoids. We used IR62 as a variety with resistance to Nilaparvata lugens (Stål) [BPH], Sogatella furcifera (Horváth) [WBPH] and Nephotettix virescens (Distant) [GLH], and IR64 as a susceptible control. The herbivores were more abundant during wet season sampling in low-nitrogen plots. During this study, parasitoids killed between 31 and 38% of BPH eggs and 24 and 52% of WBPH eggs during four days of field exposure. Parasitism, mainly due to Oligosita spp., was generally higher in high-nitrogen and IR64 plots. Similar densities of eggs in exposed plants suggest that these trends were mediated by semiochemicals and therefore support the Optimal Defense Hypothesis. Honeydew from BPH on IR62 had more xylem-derived wastes than honeydew on IR64. We applied honeydew from both varieties to sentinel plants. Parasitism by Anagrus spp. was higher on plants of either variety treated with honeydew derived from IR62; however, the effect was only apparent in high-nitrogen plots. Results suggest that Anagrus spp., by responding to honeydew, will counter the nitrogen-induced enhancement of planthopper fitness on resistant rice.

Identifying the Biological Characteristics Associated with Oviposition Behavior of Tea Leafhopper Empoasca onukii Matsuda Using the Blue Light Detection Method.

Simple SummaryThe tea leafhopper (Empoasca onukii Matsuda) is currently one of the most threatening pests in tea gardens in China. To locate and count tea leafhopper eggs, stereomicroscopy is a conventional method by dissecting the tender tissues, which is both time- and labor-consuming. The scarcity of a verified method to directly observe and investigate intact eggs within tea shoots impedes the research efforts to test the oviposition behavior of E. onukii. Herein, comparing against the stereomicroscope detection method (SMDM), we evaluated the blue light detection method (BLDM), a technique recently developed for other species in detecting E. onukii eggs directly and non-destructively within the tender shoot for four tea cultivars. The conclusion indicated that BLDM could correctly measure the egg laying quantity of E. onukii on intact tea shoots, and its accuracy was not affected by both tea cultivars and egg density in the tender shoot. Furthermore, the biological characteristics concerning the oviposition behaviors that have rarely been reported previously for E. onukii were investigated using the BLDM. Our findings provide insights for the basic research and theoretical evidence, and allow the follow-up studies for the strategy and mechanism associated with the egg laying behavior of E. onukii.Tea leafhopper (Empoasca onukii Matsuda) is amongst the key pests in tea plantations around the East Asian region. Stereomicroscopy is a conventional method used for detecting tea leafhopper eggs by dissecting the tender tissues. However, there is a need for a faster and more efficient method to directly observe and investigate intact eggs within tea shoots. The absence of a proven method limits research efforts for determining the oviposition behavior of E. onukii. Herein, we applied the blue light detection method (BLDM), a technique recently developed for other species, in order to detect E. onukii eggs directly and non-destructively within the tender shoot. In addition, we compared BLDM against the traditional stereomicroscope detection method (SMDM) for four tea cultivars. Notably, our results revealed that BLDM was precise and effective in measuring the egg laying quantity of E. onukii on intact tea shoots. Neither tea cultivars nor egg density in the tender shoot significantly affected the accuracy of BLDM. Furthermore, biological characteristics that have rarely been reported previously for E. onukii were investigated using the BLDM, including zygote duration, ovipositional rhythm, egg distribution within the tender shoot, and in different leaf positions, numbers of eggs laid by a single female daily, and laid by the entire generation. Therefore, these findings provide insights into the basic and theoretical evidence for the strategy and mechanism associated with the oviposition behavior of E. onukii.

Egg Parasitoids of Dalbulus maidis (Hemiptera: Cicadellidae) Within Maize Agroecosystems and in the Edge Zones of Maize Fields, and on Maize Varieties During the Wet Season in Mexico.

Little is known about Dalbulus maidis (DeLong) egg parasitoids within maize fields, in the edge zones that surround these fields, and the parasitism on D. maidis eggs oviposited on different maize varieties. The objectives of the present study were first to understand which egg parasitoid species attack D. maidis eggs within maize fields and in the surrounding edge zones, and second, to compare parasitism on two maize varieties (land race Ancho-pozolero and hybrid Tigre-Asgrow) during the maize-growing wet season. We used maize plants with sentinel eggs to attract the egg parasitoids in two consecutive wet seasons, in 2015 and 2016. In 2015, Anagrus sp. (Hymenoptera: Mymaridae) and Paracentrobia sp. (Hymenoptera: Trichogrammatidae) parasitized D. maidis eggs within the maize field and on its edges. However, much more parasitism was seen within the maize agroecosystem than in the maize edge zones. In 2016, two Mymaridae species, Anagrus columbi Perkins and Anagrus sp, and two Trichogrammatidae genera, Pseudoligosita sp. and Paracentrobia sp., attacked the D. maidis eggs laid on maize hybrids but not those oviposited on the maize land race. Our findings indicate that parasitism of corn leafhopper eggs differs with agroecosystem location and maize varieties.

Factors shaping life history traits of two proovigenic parasitoids.

What shapes the relative investment in reproduction versus survival of organisms is among the key questions in life history. Proovigenic insects mature all their eggs prior to emergence and are short lived, providing a unique opportunity to quantify their lifetime investments in the different functions. We investigated the initial eggloads and longevity of 2 proovigenic parasitoid wasps: Anagrus erythroneurae and Anagrus daanei, (Hymenoptera: Mymaridae) that develop within leafhopper eggs in both agricultural vineyards and natural riparian habitats in Northern California. We collected Vitis spp. leaves containing developing parasitoids from 3 natural sites (Knight Landing, American River and Putah Creek) and 3 agricultural vineyards (Solano Farm, Davis Campus and Village Homes). We recorded eggloads at parasitoid emergence and female parasitoid longevity with or without honey-feeding. Theory predicts that parasitoids from vineyards (where hosts are abundant) would have higher initial eggloads and lower longevity compared with parasitoids from riparian habitats (where hosts are scarce). Although host density and parasitoid eggloads were, indeed, higher in vineyards than in riparian habitats, parasitoid longevity did not follow the predicted pattern. Longevity without feeding differed among field sites, but it was not affected by habitat type (natural vs agricultural), whereas longevity with feeding was not significantly affected by any of the examined factors. Moreover, longevity was positively, rather than negatively, correlated with eggloads at the individual level, even after correcting for parasitoid body size. The combined results suggest a more complex allocation mechanism than initially predicted, and the possibility of variation in host quality that is independent of size.

Leafhopper, Jacobiasca lybica (Bergevin And Zanon) (Hemiptera: Cicadellidae) On Okra Plants And Associated Parasitoids

The current study was conducted in 2016 at two locations; Sakha and El-Riad, Kafr El-Sheikh governorate. Okra plants were sown at rice borders, canals and dikes at Sakha Agricultural Research Station, and as a solid crop at El-Riad in an area of 1000 m2. At both locations, okra plants were naturally infested by the leafhopper, Jacobiasca lybica (Bergevin and Zanon) (Hemiptera: Cicadellidae). To determine the parasitoids associated with the leafhopper, okra leaves having the eggs and nymphs of the leafhopper were picked up. The eggs and nymphs were excluded and incubated into petri dishes to be monitored for the possible emergence of parasitoids. One leafhopper nymph, collected from okra in rice fields, was found to be parasitized by Aphelopus sp. (Dryinidae: Hymenoptera). The leafhopper eggs collected from okra in rice fields or solid okra, hatched for four egg parasitoids. Three species; Anagrus spp., Anagrus atomus L., Stethynium sp. are belong to Mymaridae, and one parasitoid, Oligosita sp. belong to Tricogrammatidae. Anagrus parasitoids were the most abundant, while other parasitoids were found in low populations. To study the population fluctuations of the leafhopper adults and associated parasitoid, Anagrus spp., yellow sticky traps were fixed close to okra plants at both locations. J. lybica exhibited three peaks of occurrence at each location, while the parasitoid exhibited three peaks on okra surrounding rice fields, and two peaks on solid okra. It was concluded that okra plants in rice fields received higher numbers of parasitoids than solid okra.

Identification of Candidate Odorant-Binding Protein and Chemosensory Protein Genes in Cyrtorhinus lividipennis (Hemiptera: Miridae), a Key Predator of the Rice Planthoppers in Asia.

Cyrtorhinus lividipennis Reuter (Hemiptera: Miridae) is an important predatory natural enemy of planthopper and leafhopper eggs in Asian rice paddy fields. Cyrtorhinus lividipennis is known to rely largely on herbivore-induced plant volatiles to identify eggs embedded in rice stem tissues for feeding and on pheromones for mating. However, exactly how C. lividipennis decode these chemical information is unclear. In most insects, the odorant-binding proteins (OBPs) and the chemosensory proteins (CSPs) are essential for seeking out food resources and mates. In this study, we identified 10 OBP and 5 CSP genes in C. lividipennis and investigated their expression patterns in various tissues of adult males and females by quantitative real-time PCR (qRT-PCR). Six OBP genes (ClivOBP1, 2, 4, 6, 9, and 10) were mainly expressed in the male antennae, whereas three genes (ClivOBP3, ClivOBP7, and ClivOBP8) had high expression in the female antennae. ClivCSP1 was predominantly expressed in the male antennae. These findings suggest that most ClivOBPs and ClivCSPs are likely involved in food-searching behavior. The recognition of the pheromone molecules provides the basis for further functional studies on the chemoreception system of C. lividipennis.

Effects of habitat type and spatial scale on density dependent parasitism in Anagrus parasitoids of leafhopper eggs

The ability of parasitoids to maintain a high rate of parasitism under varying conditions is considered crucial to their ability to control the populations of their hosts. Here, I tested parasitism rate by Anagrus parasitoids and its dependency on the density of Erythroneura leafhopper eggs at two spatial scales (leaf and field) and two habitat types (natural vs. agricultural). The rate of parasitism differed among field sites, increased across the season, and was similar in natural and agricultural sites. At the leaf scale, the rate of parasitism was density-independent or inversely density-dependent, consistent with a weak aggregation of parasitoids on leaves with high host densities and with limited oviposition-rate or egg supply. At the field scale, in contrast, parasitism rate was positively dependent on host density, which may be explained by demographic processes, such as higher recruitment and higher fecundities of females in host-rich field sites. Overall, the results demonstrate that parasitism patterns are highly dynamic in time and space and depend on the scale of observation.

The link between host density and egg production in a parasitoid insect: comparison between agricultural and natural habitats

SummaryTheory predicts that organisms should invest more heavily in overcoming factors that more frequently emerge as the primary constraints to fitness, and especially, those factors that constrain the fitness of the most highly reproductive members of the population.We tested the hypothesis that the fecundity of a pro‐ovigenic parasitoid (where females emerge with their full egg load) should be positively correlated with the mean expectation for oviposition opportunities in the environment. More specifically, we tested whether females from agricultural systems, where hosts are often relatively abundant, emerge with more eggs than those from natural habitats.We studied the pro‐ovigenic parasitoid waspAnagrus daanei, which parasitizes eggs of leafhoppers of the genusErythroneura.Erythroneuraspp. leafhoppers feed onVitisspp. (grapes) and are major pests of commercial vineyards as well as common herbivores of wildVitis californica, which grows in riparian habitats. We sampled leafhoppers and parasitoids from eight vineyards and eight riparian habitats in centralCalifornia.We found that leafhopper density was higher at vineyards than in riparian habitats, whereas leafhopper egg volume and parasitoid body size did not differ among these habitat types. Parasitoids from vineyards had higher egg loads than parasitoids from wild grapes, and fecundity was positively related to host density across field sites. Parasitoid egg volume was larger in natural sites; however, this variation was not significantly correlated with host density across field sites. Within a single population of parasitoids collected from a vineyard, parasitoid egg load was negatively correlated with longevity, suggesting a trade‐off between reproduction and life span.The results may be explained by a rapid evolution of reproductive traits in response to oviposition opportunities; or alternatively, by the occurrence of maternal effects on the fecundity of daughters based on the foraging experience of their mothers.The ability of parasitoid fecundity to track mean host availability is likely to modulate the likelihood that parasitoid fitness will be constrained by a shortage of eggs and strengthen the ability of parasitoids to suppress the population densities of their hosts.

Regulated Deficit Irrigation Effect on Yield and Wine Color of Cabernet Sauvignon in Central California

Regulated deficit irrigation (RDI) is a management strategy that on grape can improve shoot/fruit ratio, water efficiency, and wine quality but has the potential to reduce yield. As part of a study on the influence of RDI on leafhopper density, we evaluated the effects on grape yield, berry size, berry soluble solids, and wine color. The studies were conducted at commercial vineyards in the San Joaquin Valley and in the Paso Robles region, CA, with Cabernet Sauvignon as the cultivar. Water deficits were imposed at either 50% (moderate deficit) or 25% (severe deficit) of standard irrigation (the control) for a period of 3 or 6 weeks and initiated at berry set, leafhopper egg hatch, or veraison. Deficit irrigation decreased berry weight by 16.1% at the San Joaquin Valley site (Aliso) and 11.7% at one of the Paso Robles sites (Frankel) but did not differ at the other site (Steinbeck). Yield was decreased by the deficits by 18.1% at Aliso, 26.7% at Frankel 2001 (but not 2002), and 24% at Steinbeck. Wine color density was increased by 21.8% at Aliso, 34.4% at Frankel 2001 (but not 2002), and did not differ at Steinbeck. Soluble solids did not differ among treatments at any site. There was no difference in berry weight, yield, or color between the moderate and severe deficits. It appears that in central California, RDI such as these are likely to reduce yield but are only one factor among many variables affecting quality such as wine color.

Influence of Intensity and Duration of Regulated Deficit Irrigation on <I>Erythroneura elegantula</I> (Hemiptera: Cicadellidae) on Grape

We conducted studies in a Paso Robles, CA, grape (Vitis vinifera L.) vineyard in 2002 and 2003 to estimate the impact of regulated deficit irrigation (RDI) intensity and duration on western grape leafhopper, Erythroneura elegantula Osborn. Treatments were based on deficit intensity, 50 and 25% of standard irrigation (moderate and severe deficits, respectively), and deficit duration, 3 or 6 wk time, initiated at the grape phenological stage of berry set. The standard irrigation served as the control, and was intended to be as close to 100% of evapotranspiration (1.0 ETc) for grape in this area. Each week we took counts ofleafhopper nymphs and estimated stomatal conductance, and at the end of each leafhopper generation we counted live, hatched and parasitized leafhopper eggs. Second generation leafhopper nymphal density was lowered by about 38 and 70% in 2002 and 2003, respectively, but in 2003 only the severe deficit had a negative effect on the third generation. This same pattern was seen in oviposition: second generation egg density was reduced by about 44% in the deficit treatments, but in the third generation only the severe deficit was lower than the control. There was little difference between the 3 vs. 6 wk duration in nymphal or egg density. The differences among treatments in second generation peak nymphal density were greater than the differences in second generation hatched eggs, suggesting that in addition to egg mortality, the deficits also affected nymphal mortality. Management strategies for maintaining leafhopper density low in the second generation and third generations include maintaining a sub-1.0 ETc irrigation strategy after the main RDI period, or reinstating the RDI to correspond to the third generation.

Biological Investigations on Some Species of Anagrus (Hymenoptera, Mymaridae), Egg Parasitoids of Leafhoppers (Hemiptera)

Biological investigations were carried out on entomophagous parasitoids of leafhopper eggs associated with Juncus in South Wales, U.K. The hosts and parasitoids were reared in cages in greenhouse at the temperature of 22C. The life cycle and seasonal changes of Anagrus were examined in the laboratory and in the field. Process of emergence, movement, searching for host eggs, copulation, and oviposition were also observed. Five species of Anagrus were found parasitizing leafhopper eggs. The ratio of males to females was found about one to one. The possibility of infestation depends highly on host eggs laid in living plant tissues. A female contains about 46 ovarial eggs but only 50% are laid in host eggs. In laboratory condition (+22C) the period of development is about 15 to 20 days for one generation but in natural condition in May and June the first two generations require about 25 to 55 days each.The adult parasitoids disappear at the beginning of cold weather which starts by the middle of October to middle of November. Their development stages spend the winter in the host eggs. The Mymarids produce a high infestation rate of host eggs (often 50 to 70%). Some of their hosts such as Cicadella viridis (L.) (Cicadellidae) and Conomelus anceps Germar (Delphacidae) are important pests. Five closely related species found during investigation attacking leafhopper eggs in Juncus stems are Anagrus ensifer Debauche, A. breviphragma Sokya,, A. incarnatus Haliday, Anagrus sp. A and Anagrus sp. B. This preliminary nomenclature is used because the taxonomy of this group is complex and species identification is difficult. Anagrus species emerged during investigations were found to be highly specific. Each species was restricted to the eggs of one host species in Juncus. Anagrus ensifer Debauche and A. breviphragma Sokya were found to be gregarious, the remaining species as solitarious. Egg parasitoids have the advantage that they attack the early life history stages of the pests before damage can be done. The relatively high rate of reproduction, and the short period of development are the main reasons for the great efficiency of these parasites.

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 (Gothe) (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.

Adult phenology and abundance of Froggatt's apple leafhoppper (Edwardsiana froggatti (Baker)) (Hemiptera: Cicadellidae) and its egg parasitoids, Anagrus spp. (Hymenoptera: Mymaridae), under three pest management programmes in Central Otago, New Zealand.

Froggatt's apple leafhopper, Edwardsiana froggatti (FALH), is a minor pest of apples in New Zealand. The eggs are attacked by several species of the mymarid genus Anagrus. The phenology of the leafhopper and these parasitoids in Central Otago has not been previously described. Leafhopper and Anagrus spp. adults were monitored with sticky traps in apple blocks under conventional, integrated, and organic management at the Clyde Research Centre from 1995 to 2001. The leafhopper had two generations per year and timing was similar to that reported for Canterbury and Nelson, with first generation adults occurring each season from the end of November to the end of January, and the second generation from the end of January to late April/May. Apart from a small number of Anagrus spp. adults that emerged in October/early November, the first generation began at the end of November, coinciding with the start of adult FALH flight and hence egg-laying, and continued to late February. The second generation began shortly after this and continued through to May. In addition to the evident synchrony between Anagrus spp. flight and leafhopper egg production, the trap catches indicated a strong numerical response of Anagrus spp. to rising leafhopper populations following the removal of organophosphate insecticides under integrated fruit production. This contributed to circumstantial evidence that, after 3-4 seasons, these parasitoids were the primary natural enemies that reduced leafhopper populations below economically-damaging levels; this was supported by similar evidence from apple blocks under organic management. Further research is needed to confirm this evidence of biological control by Anagrus spp., and the roles of the different species in the apple-growing regions of New Zealand.

Regulated Deficit Irrigation and Density of <I>Erythroneura</I> spp. (Hemiptera: Cicadellidae) on Grape

This study looked at regulated deficit irrigation (RDI) on leafhoppers in the genus Erythroneura (Erythroneura elegantula Osborn, or western grape leafhopper, and Erythroneura variabilis Beamer) (Hemiptera: Cicadellidae), which are serious pests of cultivated grape (Vitis vinifera L.) in California. RDI is an irrigation strategy that reduces irrigation during a critical point in the phenology of a cultivated perennial crop, to improve vegetative balance and crop quality. Erythroneura spp. are known to respond negatively to vine water stress, and the second generation ofleafhoppers begins during a potential RDI initiation period, between berry set and veraison (beginning of fruit maturation). In experiments at commercial wine grape vineyards, I imposed deficits of between 25 and 50% of crop full evapotranspiration (ET(c)) between berry set and veraison, with control treatments based on the growers' standard irrigations (typically between 0.8 and 1.0 ET(c)), and then we counted leafhopper nymphs weekly, and leafhopper eggs after the second generation. Results show a consistent reduction of second generation nymphal density with this type of RDI, with average density approximately 50% lower under deficit treatments in all three studies. Deficit irrigation reduced second generation egg density by 54% at one site and by 29.9% at another. These results confirm previous studies regarding the sensitivity of Erythroneura spp. to grapevine water stress, and, in addition, they show that a season-wide irrigation deficit is not necessary for reduction in leafhopper density. Results suggest that lower oviposition at least partly explains the lower nymphal density in the deficit treatments.