Lugens Eggs Research Articles

The N-terminal subunit of vitellogenin in planthopper eggs and saliva acts as a reliable elicitor that induces defenses in rice.

Vitellogenins (Vgs) are critical for the development and fecundity of insects. As such, these essential proteins can be used by plants to reliably sense the presence of insects. We addressed this with a combination of molecular and chemical analyses, genetic transformation, bioactivity tests, and insect performance assays. The small N-terminal subunit of Vgs of the planthopper Nilaparvata lugens (NlVgN) was found to trigger strong defense responses in rice when it enters the plants during feeding or oviposition by the insect. The defenses induced by NlVgN not only decreased the hatching rate of N.lugens eggs, but also induced volatile emissions in plants, which rendered them attractive to a common egg parasitoid. VgN of other planthoppers triggered the same defenses in rice. We further show that VgN deposited during planthopper feeding compared with during oviposition induces a somewhat different response, probably to target the appropriate developmental stage of the insect. We also confirm that NlVgN is essential for planthopper growth, development, and fecundity. This study demonstrates that VgN in planthopper eggs and saliva acts as a reliable and unavoidable elicitor of plant defenses. Its importance for insect performance precludes evolutionary adaptions to prevent detection by rice plants.

Brown Planthopper Egg Parasitization in Rice Fields with Different Growth Ages

The brown planthopper, Nilaparvata lugens Stål. (Hemiptera: Delphacidae), is one of the most important pests attacking rice plants. One of the strategies to control this pest is by using natural enemies, including egg parasitoids. This study aimed to investigate the species of N. lugens egg parasitoids and their parasitism levels in one rice ecosystem with different growth stages. The research was conducted by selecting three rice plots aged 3, 6, and 10 weeks after planting. Potted rice plants with N. lugens eggs were placed in those rice plots for two days and recollected for observations. The same release was repeated 3 weeks later at the same rice plots in the same site. Egg parasitoids of N. lugens found during this study were Oligosita sp. and Anagrus sp. The highest number of egg parasitoids were found at the rice plants aged 6 weeks after planting with 14.50 and 13.50 individuals collected during first and second trapping, respectively. In addition, the level of parasitism ranged from 6.89-22.26% with the highest parasitism was occurred in the 6-week old rice. These findings may suggest that different rice planting dates may benefit the egg parasitoids of N. lugens which could reduce the risk of outbreaks.

The Diversity and Abundance of Egg Parasitoids in Brown Planthopper, Nilaparvata lugens Stål. (Hemiptera: Delphacidae) at Different Rice Growth Phases in Saketi, Pandeglang, Banten

An extensive study about egg parasitoid biodiversity in different plant growth stages is an important need. This study was aimed to determine the diversity and abundance of egg parasitoids Nilaparvata lugens on different rice growth stages in Saketi, Pandeglang, Banten. The parasitoids sample was collected three times with two days interval sampling in three villages, i.e. Sodong (location I), Sindanghayu (location II), and Sukalangu (location III) from February to September 2018. Ten plants (as bait: rice that infected by N. lugens eggs) were put during two days along the transect line (100 meters) with 10 m space in between. The findings revealed that the abundance richness (S), the diversity index (H'), and similarity (J') of egg parasitoids of N. lugens were higher in the location I than those in the locations II and III. The study indicated that the diversity and abundance of egg parasitoids of N. lugens decreased in the generative phase of rice growth.

Effects of Vegetation Strips, Fertilizer Levels and Varietal Resistance on the Integrated Management of Arthropod Biodiversity in a Tropical Rice Ecosystem.

Integrated biodiversity management aims to conserve the beneficial species components of production ecosystems and reduce the impacts of pests. In 2011 and 2013, experiments were conducted at Los Baños, Laguna, Philippines, to compare arthropod communities in rice plots and on levees with and without vegetation strips. Vegetation strips included spontaneous weeds, sesame and okra (2011), or mung bean (2013). The plots were treated with one of three nitrogen levels and in one experiment were planted with planthopper-resistant (IR62) and susceptible (IR64) rice varieties. Parasitoids and predators of lepidopteran pests and of the ricebug, Leptocorisa oratorius, were more abundant in high-nitrogen rice plots where their prey/hosts also had highest densities. Planthoppers and leafhoppers were more abundant in low-nitrogen plots. Weedy and sesame/okra bunds provided habitat for a range of natural enemies including spiders, parasitoids and predatory bugs, but did not have higher pest numbers than cleared bunds. Higher abundances of the predator Cythorhinus lividipennis and higher parasitism of planthopper (Nilaparvata lugens) eggs by Anagrus sp. were associated with sesame/okra bunds in late season rice plots. Mung bean also provided habitat for key predators and parasitoids that spilled over to adjacent rice; however, mung bean was also associated with higher numbers of lepidopteran and grain-sucking pests in the adjacent rice, albeit without increased damage to the rice. For ricebug in particular, damage was probably reduced by higher parasitoid:pest ratios adjacent to the vegetation strips. Varietal resistance and mung bean strips had an additive effect in reducing abundance of the planthopper Sogatella furcifera and the leafhopper Nephotettix virescens. Reduced numbers of these latter pests close to vegetation strips were often compensated for by other plant-sucking bugs, thereby increasing the intensity of potentially stabilizing interspecific interactions such as competition. We highlight the benefits of diversifying rice landscapes and the need to optimize vegetation strips, e.g., by including lepidopteran trap-plants, for intensive rice production systems.

Role of different habitats for the functional response of Crytorrhinus lividipennis (Hemiptera: Miridae) on Nilaparvata lugens (Hemiptera: Delphacidae)

ABSTRACTThe functional response of a predator, Cyrtorrhinus lividipennis, on the brown planthopper, Nilaparvata lugens, was investigated in two different experimental habitats: a piece of tiller in a petri dish (5.5 cm in diameter) and a rice plant in a net cage (5.5 cm diameter × 43 cm height) for 24 h at room temperature. In the petri dish experiment, 2nd–5th instar nymphs, adult male, and female C. lividipennis were introduced in separate experiments to eggs of N. lugens at densities of five, 10, 20, 30, and 40 eggs per piece of rice. In the rice plant experiment, each C. lividipennis was introduced to a cage with a rice plant containing N. lugens eggs. After 24 h, the number of dead eggs and remaining eggs were counted and data fitted to three functional response models. Among the three types of functional responses, Type II best described the predator response to host densities in N. lugens in both experimental habitats, according to the logistic regression analysis value. The results showed that C. lividipennis was a more effective predator in the rice plant experiment compared to the disc experiment. Additionally, the searching efficiency and handling time parameters were different in the two different experimental habitats. This may cause errors when applying the functional response to biological control and predator–prey models. Different habitats and other environmental conditions from the experiment and natural rice field have to be considered.

Numerical Response of Cyrtorhinus lividipennis (Hemiptera: Miridae) to Nilaparvata lugens (Hemiptera: Delphacidae)1

Abstract Laboratory studies of the numerical response of the predator Cyrtorhinus lividipennis Reuter to its natural prey, Nilaparvata lugens Stal, determined the reproductive response to number of eggs oviposited, prey-dependent birth rate, prey-dependent mortality rate, and life cycle duration to different densities of N. lugens eggs. The experiments were conducted in cages with 1, 5, 10, 15, 20, and 30 eggs/predator per cage with 20 replications. The results indicated that the numerical response of C. lividipennis was positively related to prey density, with greater amounts of eggs laid, a longer duration of the lifespan, and adult age observed at a high prey density than a low prey density. However, the sex ratio and adult longevity were not affected by the prey density. The minimum prey density for completing C. lividipennis development was 5 eggs/d, whereas the minimum number of prey needed to produce an egg was 10 eggs/d. The study of the numerical response provided data for calculating the prey-de...

Hopper parasitoids do not significantly benefit from non-crop habitats in rice production landscapes

Agricultural intensification threatens biodiversity and ecosystem functioning. Promoting ecosystem services, such as biological pest control, could help to reduce pesticide inputs while simultaneously sustaining a high productivity. The highly intensive rice production in Southeast Asia, where more than 20% of the world's rice yield is produced, is challenged by devastating losses each year due to rice hoppers. This poses a great threat to the more than 3.5 billion people depending on rice as staple food. Egg parasitoids are among the most important natural enemies of rice hoppers and might be promoted with effective habitat management. However, empirical studies that focus on the management of parasitoid populations to enhance biological pest control in rice agroecosystems are largely lacking. We therefore analysed the effects of the availability of diverse habitats on hopper parasitoid performance, parasitism rates and pest control services, hypothesising that egg parasitoid abundance and pest control is positively influenced by diverse non-crop areas, which provide food resources as well as retreat areas for the fallow season.We experimentally tested the efficiency and abundance of egg parasitoids of Nilaparvata lugens and Nephotettix spp. in three study sites representing different levels of floral resources over the course of two rice growing seasons. We used mixed effect models to test whether habitat diversity positively influenced parasitoid abundance and subsequently reduces hatching rates of the hopper nymphs.Nephotettix spp. eggs were parasitized by Gonatocerus spp. and Paracentrobia spp. by 92.5%; Nilaparvata lugens eggs were parasitized by Oligosita spp. and Anagrus spp by 93%. In contrast to our hypothesis, we could demonstrate that additional floral resources do not significantly enhance parasitoid abundance and pest control in rice agroecosystems. Up to six times more parasitoids hatched from the bait plants exposed in the monoculture compared to the non-crop areas (p<0.05). All parasitoid genera except Anagrus spp. were found in rice fields in triple or quadruple numbers compared to the non-crop habitats (p<0.05). This was true also during the fallow period (p<0.05), where only ratoon rice was available to sustain hopper populations.In contrast to our hypotheses and findings from temperate productions systems, we found higher parasitoid abundance during all crop stages and increased hatching rates in the monocultures than in the non-crop habitats. The structural and temporal heterogeneity of rice crops and ratoon rice within the production area seemed to be sufficient to sustain high densities of parasitoid populations. We conclude that ecological intensification schemes should implement asynchronous planting cycles in rice systems to maintain or enhance parasitoids populations and their biocontrol services. In combination with reduced pesticide inputs, these measures might help to avoid yield losses due to rice hoppers in the future.

A banker plant system of 'Leesia sayanuka-Nlilaparvata muiri-Tytthus chinensis' to control rice planthoppers

In order to clarify the feasibility of the banker plant system "Leesia sayanuka-Nlilaparvata muiri-Tytthus chinensis" to control rice planthooper, the effects of the combination of rice, L. sa-yanuka, N. lugen and N. muiri on the adult morphology, population growth, oviposition and feeding selectivity of T. chinensis were carried out in the present study. The results showed that the body size of male and female adults of T. chinensis rice population (feeding on N. lugens eggs) were significantly larger than those of T. chinensis population (feeding on N. muiri eggs). Population growth parameters including fecundity, net productive rate, innate capacity for increase, finite rate of increase of L. sayanuka feeding on N. lugens eggs were significantly higher than those of L. sayanuka feeding on N. muiri eggs. However, the population growth ability of L. sayanuka feeding on N. muiri was still high enough to expand the population. For the oviposition selection, both rice population and L. sayanuka population preferred laying eggs on rice than on L. sayanuka. Meanwhile, there was no significant difference in the predation of females, males and nymphs to N. lugens eggs or N. muiri eggs between rice population and L. sayanuka population. At last, based on our results, we discussed the feasibility of establishing the banker plant system "L. sayanuka-N. muiri-T. chinensis" in rice fields.

Development, reproduction and longevity of Aprostocetus sp. (Hymenoptera: Eulophidae), an egg parasitoid of the Brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

Aprostocetus sp. (Hymenoptera: Eulophidae) is an egg parasitoid of Nilaparvata lugens (Stål) (Hemiptera: Delphacidae). This parasitoid was surveyed and collected from paddy fields in Nonthaburi and Pathum Thani provinces, Thailand. Aprostocetus sp. was reared on N. lugens eggs under laboratory conditions at the National Biological Control Research Center, Kasetsart University, Bangkok, Thailand. The development time, reproductive performance and adult longevity of Aprostocetus sp. were investigated. The development time of Aprostocetus sp. took 12–19 d; the mean development time of female and male wasps was 15.4 ± 1.3 and 14.8 ± 1.3 d, respectively. The mean daily offspring production was 3.5 ± 0.6 wasps; total offspring production was 74.7 ± 33 wasps; and the sex ratio (female to male) was 1.8:1. The longevity of adult female wasps fed with honey and without honey was 5.3 ± 0.88 and 1.9 ± 0.14 d, respectively. The longevity of adult male wasps fed with honey and without honey was 1.9 ± 1.2 and 1.4 ± 0.5 d, respectively. The longevity was significantly (p < 0.05) different between food sources for both females and males.

CrylAb rice does not impact biological characters and functional response of Cyrtorhinus lividipennis preying on Nilaparvata lugens eggs

One concern about the use of transgenic plants is their potential risk to natural enemies. In this study, using the eggs of the rice brown planthopper, Nilaparvata lugens, as a food source, we investigated the effects of Cry1Ab rice on the biological characteristics and functional response of an important predator Cyrtorhinus lividipennis. The results showed that the survival ability (adult emergence rate and egg hatching rate), development (egg duration, nymphal developmental duration), adult fresh weight, adult longevity and fecundity of C. lividipennis on Bt rice plants were not significantly different compared to those on non-Bt rice plants. Furthermore, two important parameters of functional response (instantaneous search rate and handling time) were not significantly affected by Bt rice. In conclusion, the tested Cry1Ab rice does not adversely impact the biological character and functional response of C. lividipennis.

Analisis senyawa volatil dari ekstrak tanaman yang berpotensi sebagai atraktan arasitoid telur wereng batang coklat, Anagrus nilaparvatae (Pang et Wang) Hymenoptera: Mymaridae)

Plants produce volatiles as communication cues intra- or inter- species. Infested plants by herbivores will produce volatiles as indirect defense mechanism that attracts natural enemies of herbivores. Analysis of volatiles compounds produced by rice plant as result of infested brown plant hopper (BPH), Nilaparvata lugens Stâl, was done to identify compounds in the volatiles that potentially can be used as attractant for egg parasitoids of BPH, Anagrus nilaparvatae (Pang et Wang) (Hymenoptera: Mymaridae). This research was an early stage to develop formulation of parasitoid attractant. The research activities include volatiles extraction of infested rice stem by BPH eggs using acetone, n-hexane as the extraction solvents; analyses of volatile compounds with GC-MS; and bioassay of parasitoid orientation behavior to the volatiles using olfactometer methods. Extraction methods applied were maceration and continuous extraction followed by concentration. Bioassay on the parasitoid orientation behavior was done by using Y-tube olfactometer and every lot of bioassay using 30 parasitoid females with 3 replicates. The results showed that the volatile compounds of extract of infested rice stem by BPH eggs comprise of 16 components. The highest proportion of the components extracted with acetone is 2-Pentanone, 4-hydroxy-4-methyl (19,9%), while those with n-hexane is Hexanedioic acid, dioctyl ester (65%). A. nilaparvatae showed positive response to the volatiles extracted from infested rice plant by N. lugens eggs. Therefore, the volatiles can be used as an attractant for the egg A. nilaparvatae to support rice pest management.

Laboratory screening supports the selection of sesame (Sesamum indicum) to enhance Anagrus spp. parasitoids (Hymenoptera: Mymaridae) of rice planthoppers

Planthopper (Delphacidae) pests have broken out frequently in Asia over the last decade leading to interest in enhancing the impact of natural enemies by growing nectar plants on the bunds that border rice fields. Such targeted use of plant diversity is popular in other crop systems but there is a marked lack of information on the scope for its use in rice, particularly the important aspect of which plant species to use. This study used Y-tube olfactometer assays to measure the response of two important parasitoids of delphacid pests to candidate nectar plants. Anagrus optabilis exhibited significant attraction to the air from six of the seven plant species whilst Anagrus nilaparvatae appeared more selective, exhibiting attraction to only seven of the 23 plants screened and repulsion to one. Sesamum indicum, Emilia sonchifolia, and Impatiens balsamena were the only three plants attractive to both parasitoids. Laboratory longevity of adult female A. nilaparvatae and A. optabilis with access to sesame flowers was significantly greater than with access to sesame from which the flowers were removed plus water. Similarly, both parasitoids parasitized significantly more brown planthopper (Nilaparvatae lugens) eggs in the presence of sesame flowers. Handling time of A. nilaparvatae was reduced from 31.29 to 18.36min by access to sesame nectar. Findings show that sesame has a marked beneficial effect on key parameters of Anagrus spp. and justifies further evaluation of its utility as a nectar plant to improve biological control in Asian rice systems.

Sublethal effects of four insecticides on Anagrus nilaparvatae (Hymenoptera: Mymaridae), an important egg parasitoid of the rice planthopper Nilaparvata lugens (Homoptera: Delphacidae)

The egg parasitoid, Anagrus nilaparvatae (Pang et Wang) (Hymenoptera: Mymaridae), has been considered an important biocontrol agent of Nilaparvata lugens (Stål) (Homoptera: Delphacidae). Laboratory bioassays were set up to examine the sublethal effects of four insecticides, triazophos, deltamethrin, chlorantraniliprole and pymetrozine on A. nilaparvatae through contact routes. The results indicated that the sublethal concentrations (LC20 and LC10) of triazophos and deltamethrin disrupted the ability of A. nilaparvatae to perceive host–plant odor cues. After exposure to sublethal concentrations of triazophos and deltamethrin, some surviving parasitoids showed no response to volatiles from N. lugens-infested plants, and responsive survivors were equally attracted to volatiles emitted from N. lugens-infested plants and those from healthy plants. However, sublethal concentrations (the recommended field rate and half the recommended field rate) of chlorantraniliprole and pymetrozine had little impact on the foraging ability of A. nilaparvatae. More than 90% of surviving A. nilaparvatae responded to volatiles from N. lugens-infested plants, and responsive individuals were significantly attracted by host-associated odors. Surviving A. nilaparvatae exposed to sublethal concentrations of triazophos, deltamethrin, chlorantraniliprole or pymetrozine had a similar behavioral response to kairomones from N. lugens, compared with untreated parasitoids. Parasitism rate of N. lugens eggs by insecticide-treated A. nilaparvatae did not differ significantly from the untreated control. Our results suggested that the foraging ability of A. nilaparvatae was disrupted by the broad-spectrum neurotoxic insecticides triazophos and deltamethrin but not by chlorantraniliprole or pymetrozine, which belong to novel classes of insecticides with distinct modes of action. However, sublethal concentrations of triazophos or deltamethrin did not affect the behavioral response of surviving A. nilaparvatae to host kairomone. The mechanism resulting in the different behavioral responses of surviving A. nilaparvatae remains unknown and should be further studied.

Effects of imidacloprid on the orientation behavior and parasitizing capacity of Anagrus nilaparvatae, an egg parasitoid of Nilaparvata lugens

Anagrus nilaparvatae (Pang et Wang) (Hymenoptera: Mymaridae), is an egg parasitoid of rice planthoppers, Nilaparvata lugens (Stal) (Homoptera: Delphacidae). This study evaluated effects of the insecticide imidacloprid on orientation behavior and parasitizing capacity of A. nilaparvatae. Sub-lethal concentrations of imidacloprid (LC20 and LC10) disrupted the foraging ability of A. nilaparvatae exposed to imidacloprid through contact or oral routes. Some survivors did not respond to volatiles from N. lugens-infested plants. Responsive individuals were equally attracted to volatiles from N. lugens-infested and healthy plants. Volatiles emitted from rice plants treated with a low concentration of imidacloprid were more attractive to A. nilaparvatae than those from plants treated with a high concentration of imidacloprid. Parasitism of N. lugens by A. nilaparvatae that survived contact with sub-lethal concentrations of imidacloprid did not decrease significantly. When A. nilaparvatae were fed imidacloprid-honey mixture, parasitism rates were 1.49% and 0%, respectively, significantly lower than those of the control (9.58%). Parasitism of N. lugens eggs in high concentration of imidacloprid treated rice plants by A. nilaparvatae decreased significantly. These effects involving disturbed foraging ability and reduced parasitizing capacity of A. nilaparvatae indicated that imidacloprid could decrease the performance of this parasitoid.

Preference and Performance of &lt;I&gt;Anagrus nilaparvatae&lt;/I&gt; (Hymenoptera: Mymaridae): Effect of Infestation Duration and Density by &lt;I&gt;Nilaparvata lugens&lt;/I&gt; (Homoptera: Delphacidae)

The effect of Nilaparvata lugens (Stål) infestation duration and density on the host preference and performance of Anagrus nilaparvatae Pang et Wang, an egg parasitoid of rice planthoppers, was determined. The results showed that the parasitoid preferred N. lugens eggs on the plants infested with 10 gravid N. lugens females for 1 d to those plants infested with 10 gravid females for 2 or 3 d. It was also found to prefer N. lugens eggs on plants infested with 10 or 20 adult females after 24 h of infestation to those plants infested with 5 or 80 females. The parasitoid's offsprings had lower survival rates, fecundities, female ratios, indexes of capacity for population increase, and longer developmental durations on plants when they were infested with high N. lugens density (80 adult females per plant). However, the performance of the parasitoid on plants infested with low N. lugens density (5 female adults per plant) was similar to those on plants with intermediate N. lugens density (10 or 20 adult females per plant). Low preference of the parasitoid for N. lugens eggs on plants with heavy or light infestation levels may be correlated with low host suitability and detectability, respectively. The result implies an important role of herbivore-induced rice volatiles in the host preference of the parasitoid A. nilaparvatae, by which the parasitoid perceives the host and its suitability.

Attraction of the Parasitoid Anagrus nilaparvatae to Rice Volatiles Induced by the Rice Brown Planthopper Nilaparvata lugens

Anagrus nilaparvatae, an egg parasitoid of the rice brown planthopper Nilaparvata lugens, was attracted to volatiles released from N. lugens-infested plants, whereas there was no attraction to volatiles from undamaged plants, artificially damaged plants, or volatiles from N. lugens nymphs, female adults, eggs, honeydew, and exuvia. There was no difference in attractiveness between plants infested by N. lugens nymphs or those infested by gravid females. Attraction was correlated with time after infestation and host density; attraction was only evident between 6 and 24 hr after infestation by 10 adult females per plant, but not before or after. Similarly, after 24 hr of infestation, wasps were attracted to plants with 10 to 20 female planthoppers, but not to plants with lower or higher numbers of female planthoppers. The attractive time periods and densities may be correlated with the survival chances of the wasps' offspring, which do not survive if the plants die before the wasps emerge. Wasps were also attracted to undamaged mature leaves of a rice plant when one of the other mature leaves had been infested by 10 N. lugens for 1 d, implying that the volatile cues involved in host location by the parasitoid are systemically released. Collection and analyses of volatiles revealed that 1 d of N. lugens infestation did not result in the emission of new compounds or an increase in the total amount of volatiles, but rather the proportions among the compounds in the blend were altered. The total amounts and proportions of the chemicals were also affected by infestation duration. These changes in volatile profiles might provide the wasps with specific information on host habitat quality and thus could explain the observed behavioral responses of the parasitoid.

Exogenous Application of Jasmonic Acid Induces Volatile Emissions in Rice and Enhances Parasitism of Nilaparvata lugens Eggs by theParasitoid Anagrus nilaparvatae

Jasmonate signaling pathway plays an important role in induced plant defense against herbivores and pathogens, including the emission of volatiles that serve as attractants for natural enemies of herbivores. We studied the volatiles emitted from rice plants that were wounded and treated with jasmonic acid (JA) and their effects on the host-searching behavior of the rice brown planthopper, Nilaparvata lugens (Stål), and its mymarid egg parasitoid Anagrus nilaparvatae Pang et Wang. Female adults of N. lugens significantly preferred to settle on JA-treated rice plants immediately after release. The parasitoid A. nilaparvatae showed a similar preference and was more attracted to the volatiles emitted from JA-treated rice plants than to volatiles from control plants. This was also evident from greenhouse and field experiments in which parasitism of N. lugens eggs by A. nilaparvatae on plants that were surrounded by JA-treated plants was more than twofold higher than on control plants. Analyses of volatiles collected from rice plants showed that JA treatment dramatically increased the release of volatiles, which included aliphatic aldehydes and alcohols, monoterpenes, sesquiterpenes, methyl salicylate, n-heptadecane, and several as yet unidentified compounds. These results confirm an involvement of the JA pathway in induced defense in rice plants and demonstrate that the egg parasitoid A. nilaparvatae exploits plant-provided cues to locate hosts. We explain the use of induced plant volatiles by the egg parasitoid by a reliable association between planthopper feeding damage and egg presence.

カタグロミドリメクラガメの繁殖特性

Developmental speed and reproductive potential of the mirid bug, Cyrtorrhinus lividipennis, were measured nuder laboratory conditions. Both nymphs and adults were supplied with rice plants onto which gravid females of Nilaparvata lugens were released. Developmental zero and cumulative heat units required for completion of the immature stages were calculated at 11.7°C and 260 day-degrees, respectively, based on the immature period measured at 20, 24, and 28°C. Mean longevities (±SD) of male and female adults at 25°C were 30.1±5.9 and 28.2±5.7 days, respectively. Female adults started oviposition 3.1 days after emegence. Lifetime fecundity of females was 291.2±83.7 eggs, which was more than 10 times as large as the largest figure so far reported for C. lividipennis. It was suggested that the presence of N. lugens females in the rearing cage provided C. lividipennis with a much better food source than the ordinarv rearinv mothnd of prouidin N. lugens eggs laid in rice plants.

Effects of Prey Number and Stage on the Biology of Cyrtorhinus lividipennis (Hemiptera: Miridae): A Predator of Nilaparvata lagens (Homoptera: Delphacidae)

When given 30 eggs of Nilaparvata lugens (Stal) daily, males and females of Cyrtorhinus lividipennis Reuter took 10.8 and 13.0 d, respectively, to develop from first instar. The males consumed 49.0 eggs and the females, 59.2 eggs. The mean body length of adult males was 2.6 mm and females, 3.1 mm; mean longevity was 9.6 d for the males and 14.4 d for the females. Lifetime egg consumption was 43.8 eggs by the males and 123.6 eggs by the females. Mean lifetime fecundity by unmated females was 34.0 eggs. When 20 or fewer eggs or 10 or fewer first-instar N. lugens were given daily as food, nymphal survival, adult longevity, and fecundity decreased. Individuals offered 20 or more N. lugens eggs consumed significantly more than those offered fewer eggs, but this did not result in a decrease in development time or in adult size. C. lividipennis adults that were fed daily with N. lugens nymphs (5 or 10 first, second, or third instars) also had a shorter life span and laid no eggs. Adults offered 10 second or third instars lived significantly longer than those on other regimes. Our results suggest that C. lividipennis nymphs need only small amounts of food to survive to adulthood under field conditions, especially at the beginning of the rice growing season, when N. lugens eggs are relatively scarce.

Resistance of wild rices, Oryza spp., to the brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae)

Of the 128 wild rices screened, 83 accessions were resistant to the brown planthopper Nilaparvata lugens (Stål). Resistant accessions were non-preferred and significantly more individuals settled on susceptible TN1 plants than on resistant ones. The quantity of food ingested and assimilated by N. lugens on resistant accessions was less than on susceptible TN1. N. lugens caged on resistant accessions had slow nymphal development, reduced longevity and low fecundity. Two wild rice species, Oryza officinalis and O. punctata, reduced the percentage hatchability of N. lugens eggs. A significant reduction in population growth was observed on resistant accessions compared with susceptible TN1.