Sitona lineatus (Coleoptera: Curculionidae) Larval Feeding on Pisum sativum L. Affects Soil and Plant Nitrogen

Adults of Sitona lineatus (pea leaf weevil, PLW) feed on foliage of several Fabaceae species but larvae prefer to feed on nodules of Pisum sativum L. and Vicia faba L. Indirectly, through their feeding on rhizobia, weevils can reduce soil and plant available nitrogen (N). However, initial soil N can reduce nodulation and damage by the weevil and reduce control requirements. Understanding these interactions is necessary to make integrated pest management recommendations for PLW. We conducted a greenhouse study to quantify nodulation, soil and plant N content, and nodule damage by weevil larvae in relation to soil N amendment with urea, thiamethoxam insecticide seed coating and crop stage. PLWs reduced the number of older tumescent (multilobed) nodules and thiamethoxam addition increased them regardless of other factors. Nitrogen amendment significantly increased soil available N (>99% nitrate) as expected and PLW presence was associated with significantly lower levels of soil N. PLW decreased plant N content at early flower and thiamethoxam increased it, particularly at late flower. The study illustrated the complexity of interactions that determine insect herbivory effects on plant and soil nutrition for invertebrates that feed on N-fixing root nodules. We conclude that effects of PLW on nodulation and subsequent effects on plant nitrogen are more pronounced during the early growth stages of the plant. This suggests the importance of timing of PLW infestation and may explain the lack of yield depression in relation to this pest observed in many field studies. Also, pea crops in soils with high levels of soil N are unlikely to be affected by this herbivore and should not require insecticide inputs.     

Factors influencing the effectiveness of Trichosirocalus horridus (Panzer) in the control of Carduus thistles

Trichosirocalus horridus (Panzer) (Coleoptera: Curcilionidae), a European weevil introduced for the biological control of Carduus thistles, was initially released in 1974 and has become established in Virginia, USA. Studies were conducted to examine the impact of the weevil on Carduus thistles in the field in spring and winter, and in the laboratory. Variables included two thistle species, two thistle sizes and three larval densities. Response of the thistle to larval infestation was influenced by thistle growth, thistle size and larval density. Thistle rosettes grown in the laboratory had the greatest percentage of plants developing necrosis (99%) with none recovering fully; the plant centre died in 89%, and 31% died completely, whereas no field-grown plants died. Spring rosettes developed the next largest percentage of necrosis (85%) and of death of centre (28%), but had the highest percentage of plants recovering (80%). Overwintering thistles developed the least amount of necrosis (43%) and of dead centres (2%), but had a lower recovery rate (61%) than spring thistle rosettes. Neither spring nor overwintering rosettes died even at the highest infestation level (50 larvae). Appearance of symptoms of infestation in overwintering thistle rosettes was influenced by plant species, plant size and rate of larval infestation. Thistle species was not a factor determining when laboratory rosettes manifested symptoms of infestation, and larval density did not influence spring rosettes. Small laboratory thistle rosettes were killed by infestations of 30 larvae (42%) and 50 larvae (100%). Although T. horridus larvae do not kill the majority of the thistles that they infest, they do weaken them by destroying crown tissues. The effectiveness of T. horridus may be greatly enhanced by the joint use of other stress factors.     

Arthropod communities related to different mixtures of oil (Glycine max L. Merr.) and essential oil (Artemisia annua L.) crops

Plants can host many herbivores and their natural enemies during their growth cycles. For this reason, changes in the relative abundance of crop and weed plants in a monocropping system as well as different crop plants in an intercropping system may produce great bottom up impacts in the specific and functional structure of spontaneous communities of arthropods. The hypothesis of this study was that the combination of two contrasting species, soybean (Glycine max, Fabaceae, N₂ fixing plant) and annual wormwood (Artemisia annua, Asteraceae, VOCs plant), would be related to different spontaneous communities of arthropods depending on the proportion of each species, and this would favor crop biodiversity without compromising crop production. The objectives of the study were: (a) to analyze the differences of spontaneous communities of arthropods related to different soybean (S)-annual wormwood (W) mixtures, using standard crop management for S production in Argentina, (b) to determine S and W total biomass and W essential oil content and yield and, (c) to analyze the relationship between arthropod communities and crop productivity. Factorial field experiments with 3 replications were done during 2006 and 2007. S density was kept constant (40 plants m⁻²) and different W densities (plants m⁻²) were added. Treatments were pure S, S + 2W, S + 4W, S + 8W and pure W (8 plants m⁻²). Arthropods were sampled at soybean full flowering and were classified in functional groups as herbivores and non-herbivores. S and W total and relative biomass and W essential oil content and yield from leaves and inflorescences were estimated in reproductive stage. Arthropod morphospecies abundance and richness were determined for each treatment. Data were analyzed using uni (ANOVA) and multivariate (CCA) techniques. Arthropods belonging to 7 orders presented a total richness of 48 morphospecies in 2006 and 36 in 2007, while total abundance was 379 in 2006 and 318 in 2007. The proportion of non-herbivores was higher than the proportion of herbivores. Different arthropod communities were observed according to each treatment. No differences were found among treatments in S + W and S total biomass production, while W total biomass and essential oil yield were both different among treatments. Relative biomass production of S and W was the main explanatory variable related to the contrast of arthropod communities between pure annual wormwood (W) and the rest of the treatments. Annual wormwood could be used as an accompanying essential oil crop or left as a weed in the densities tested in this work, favoring biodiversity and, eventually, pest management without compromising soybean crop yield.     

Smallholder farmers' knowledge,perceptions and management of pea weevil in north and north-western Ethiopia

Pea weevil (Bruchus pisorum L.) is one of the most serious insect pests of field pea (Pisum sativum L.) in Ethiopia. A survey of 400 farmers was conducted in four main pea-growing districts in north and north-western Ethiopia. The objectives were to assess farmers' knowledge and perceptions of pea weevil, to examine their current pest management practices and to identify challenges to pea weevil control, so that participatory integrated pest management for smallholder farmers in Ethiopia can be developed. The results revealed that most (71%) of the farmers surveyed had knowledge about pea weevil and were able to identify damaged seeds based on common visible symptoms of weevil infestation. However, most farmers did not know that pea weevil attacks plants in the field, but rather considered it a storage pest. The results also showed that farmers' cultural practices influence the incidence and spread of pea weevil and that most farmers did not check seed for pea weevil symptoms before planting. Only a minority of farmers (19%) harvested peas early and some harvested late, unintentionally promoting infestation and carryover of weevils. In addition, most farmers (74%) were not aware of the source and means of weevil spread on their farm and some did not clean up fallen and shattered peas during harvesting and threshing. The majority (63%) of the farmers surveyed relied on chemical insecticides, namely actellic dust and phostoxin, to treat harvested peas in storage. However, the results revealed a knowledge gap in that farmers were well aware of the problem of pea weevil, but lacked knowledge of cultural practices affecting pea weevil and of problems in the use of pesticides. This highlights the need for farmer training and for development of participatory integrated pest management methods for pea weevil.     

Area-wide suppression of boll weevil (Coleoptera: Curculionidae) populations in Nicaragua

Between 1982 and 1984, the Nicaraguan Ministry of Agricultural Development and Agrarian Reform (MIDINRA) used an area-wide network of trap crops of cotton from February to August to suppress boll weevils (Anthonomus grandis Boheman) on 17450 ha (1982–1983) and 35 200 ha (1983–1984) of cotton land in the Leon region of Nicaragua. In the 1982–1983 season the programme reduced boll weevil infestations (expressed as weevil-days) 89% in Zone II (normal rainfall area) when compared with untreated controls. This suppression of adult weevils resulted in a reduction from 18 to 10 seasonal applications of methyl parathion for weevil control. The programme reduced weevil insecticide costs per kg of raw cotton produced by an area-wide average of 43%. In the 1983–1984 season the programme reduced weevil-days by an area-wide 36% in commercial fields. In Zone II, trap cropping reduced by 40% the quantity of insecticides applied for weevil control. Weevil control costs per kg of raw cotton produced were reduced by 44%. Non-significant cost reductions for weevil control in Zone I may have been due to early drought, cattle grazing on trap crop areas, or inadequate management of trap crops. The 2-year programme was the largest mobilization of public and private resources for pest management ever undertaken in Nicaragua, and gives practical evidence that suppression of between-season boll weevil populations can form the basis for more profitable control of this key pest in the commercial cotton season.     

Resseliella sp. (Diptera: Cecidomyiidae) attacking field beans (Vicia faba L.)

In 1981 and 1982, the stems of Vicia faba in England were often infested by larvae of Resseliella sp. Attacks were widespread, most noticeable in June and July, and most frequent on winter beans, although the spring crop was also attacked. Larvae were associated with epidermal lesions, these usually being caused by Fusarium or Botrytis. It was concluded that attacks of the Cecidomyiid were secondary, exploiting existing injuries. Some insecticide treatments against Sitona lineatus also decreased infestation by Resseliella.     

Characterization of Solanum chomatophilum resistance to 2 aphid potato pests, Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer)

The aphids Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) (Hemiptera: Aphididae) are responsible for yield reduction in potato (Solanum tuberosum) production by direct phloem feeding and by spreading viruses. Breeding resistant traits from Solanum chomatophilum into the potato germplasm provides alternative means to control aphid infestations. Integrated pest management strategy, using plant resistance, benefits from the characterization of the resistance and of its impact on aphid biology. Our objective was to characterize the resistance of S. chomatophilum by assessing the effects of accessions, plant parts on aphid performance, and by assessing the impact of the resistance factors on different aphid developmental stages and on alate morph production. Detailed aphid performance was obtained by measuring fecundity, survival, percentage of nymphs that reached adult moult, and population growth using whole plant and clip cage experimental designs. Accession and plant physiological age, but not aphid developmental stage, influenced all life-history parameters, except for alate morph production which was not induced on the resistant accessions. Plant part influence was independent of plant species and accession. Both experimental designs resulted in congruent resistance levels at the accession level for each of the two aphid species, supporting the use of any of them in S. chomatophilum resistance screening. PI243340 was resistant to both aphid species, while PI365324 and PI310990 were also resistant to M. euphorbiae and M. persicae, respectively.     

Wilt disease management and enhancement of growth and yield of Cajanus cajan (L) var. Manak by bacterial combinations amended with chemical fertilizer

Root nodulating Sinorhizobium fredii KCC5 and Pseudomonas fluorescens LPK2 were isolated from nodules of Cajanus cajan and disease suppressive soil of tomato rhizosphere, respectively. Both strains produced IAA, siderophore, solubilized insoluble phosphate, showed chitinase and β-1,3-glucanase activities, and strongly inhibited the growth of Fusarium udum. It also caused degradation and digestion of cell wall components, resulting in hyphal perforations, empty cell (halo) formation, shrinking and lysis of fungal mycelia along with significant degeneration of conidia. LPK2 produced volatile cyanogen (HCN). Combinations of S. fredii KCC5 and P. fluorescens LPK2 with half dose of chemical fertilizers showed a significant increase in seed germination (94%) while seed germination with co-inoculated strains (KCC5 + LPK2), KCC5 and LPK2 alone was 90, 84 and 82% respectively as compared to control 77%. After 120 days of sowing, per plant number of pods, nodules, shoot length, root length, shoot weight and root weight were greater for the combination with half dose of chemical fertilizers compared to the control. Combinations of S. fredii KCC5 and P. fluorescens LPK2 with half dose of chemical fertilizers resulted in an 82% increase in grain yield per hectare compared to the control. Both strains KCC5 and LPK2 led to proto-cooperation as evidenced by synergism, aggressive colonization of the roots, and enhanced growth, suggesting potential biocontrol efficacy against Fusarium wilt in C. cajan.     

Impact of area-wide malathion on predatory arthropods and secondary pests in cotton during boll weevil eradication in Texas

The boll weevil, Anthonomus grandis grandis, has been eradicated from much of the cotton producing region of the US and to-date eradication efforts continue in Texas. While providing long-term economic and environmental benefits, area-wide applications of malathion used by the eradication program have been implicated in the disruption of biological control of some cotton pests. This study evaluated the impact of the area-wide boll weevil eradication on abundance of predatory arthropods and key pests of cotton during four years in central Texas. Multiple applications of malathion ULV significantly reduced seasonal mean densities of spiders, predatory bugs (Orius spp. Pseudatomoscelis seriatus, Nabis spp., Geocoris spp.), Chrysopidae larvae and red imported fire ant, Solenopsis invicta, collected from the cotton canopy. In contrast, densities of beet armyworm, Spodoptera exigua, heliothine and other lepidopteron larvae, cotton aphid, Aphis gossypii, and adult and larval convergent lady beetle, Hippodamia convergens, often increased in cotton fields under boll weevil eradication. The density of total predators measured during the mid-season (period of blooming and early boll development) was significantly and negatively correlated with density of beet armyworm larvae during the late-season (boll maturation period). Results suggest that the community of predatory arthropods in the cotton canopy, rather than one or several key predators, is important in suppressing outbreaks of S. exigua and other lepidopteran pests in cotton. Furthermore, the potential to use densities of generalist predators in mid-season to anticipate late-season outbreaks of beet armyworm during boll weevil eradication is discussed.     

Differential response of pea (Pisum sativum) to Orobanche crenata, Orobanche foetida and Phelipanche aegyptiaca

Several broomrape species including Orobanche crenata, Orobanche foetida and Phelipanche aegyptiaca are reported to infect various grain and forage legumes in the Mediterranean and West Asia. Pea (Pisum sativum) is severely damaged by O. crenata, but there are no reports on O. foetida or P. aegyptiaca infection. We report here that pea can induce high germination of seeds of O. crenata, O. foetida and P. aegyptiaca but only O. crenata success infecting pea roots and developing further. Some differences in levels of infection by O. crenata were observed among pea accessions what can be exploited in pea resistance breeding programmes. On the contrary, all pea accessions studied were highly resistant to infection by both O. foetida and P. aegyptiaca, preventing any tubercle attachment and development. This makes pea a promising candidate as trap crop for O. foetida and P. aegyptiaca seed bank demise in infested soils.     

Contributions of visual cues to cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), resistance in novel host genotypes

Herbivorous insects can demonstrate great selectivity among visual cues. The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) (syn. Ceutorhynchus assimilis (Paykull)) is also influenced by visual cues. Here, we present results of a study examining the attractiveness of flowers and foliage of Sinapis alba (a suboptimal host for larval development), Brassica napus (an excellent host for larval development) and novel lines derived from S. alba x B. napus; several of these have been demonstrated to be resistant in field and laboratory tests. Attractiveness, reflectance properties and resistance demonstrated in field trials were related. Responses to host plants differed among plant genotypes and were related to the amounts of UV and yellow reflected from flowers. Moderate UV reflectance greatly increased the attractive effects of yellow. Fewer weevils responded to test plants with greater or lesser floral UV reflectance.     

Sampling and development of economic injury levels for Anthonomus rubi Herbst adults

Field studies were conducted in northwestern Turkey from 1998–2000 to examine population dynamics of adult strawberry blossom weevils (Anthonomus rubi Herbst), and to establish economic injury levels based on the relationship between densities of overwintered adults and yield losses. Adult weevils were sampled weekly in untreated and insecticide-treated plots using a sweep net. Sweep net catches showed that the abundance of A. rubi adults had two peaks; the first between late-April and early-May, and the second between late-June and mid-July. Linear regression revealed a strong relationship between overwintered and new-generation adult densities. The overwintered-generation adults had generally higher mean population densities than the new-generation. A significant linear decrease was observed in strawberry yields as densities of overwintered-generation adults increased. Percentage yield losses varied between 1.64% and 13.42% among sites. Estimated economic injury levels ranged from 1.00 to 4.00 adults per sweep depending on the management scenario, control cost, control efficacy, and crop value.     

Thresholds of economic damage by clover seed weevil (Apion fulvipes Geoff.) and lesser clover leaf weevil (Hypera nigrirostris Fab.) on white clover (Trifolium repens L.) seed crops

Severe reductions in the seed yield of white clover can occur because of feeding by the white clover seed weevil Apion fulvipes and the lesser clover leaf weevil Hypera nigrirostris which together can reduce the seed yield by more than 0·50. From 2002 to 2006 five field experiments were carried out to investigate the relationship between the density of these two weevil species and seed yield of white clover. Damage caused by the weevils was calculated as the difference in the number of weevils and the difference in seed yield between the average of insecticide‐treated and untreated plots. Loss of seed yield was expressed as a proportion of the seed yield in insecticide‐treated plots, which allowed for a comparison between years as yields in insecticide‐treated plots varied. A multiple regression approach was chosen in which proportional loss in seed yield was the response variable and the weevils A. fulvipes and H. nigrirostris were the independent variables. Data obtained from the experiments were used to construct the following threshold model of economic damage:      

Yield and agronomic performance of maize hybrids resistant to the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

This study evaluated improved maize hybrids (Zea mays L.) with varying level of resistance to the maize weevil, Sitophilus zeamais Motschulsky, for yield and agronomic traits for two seasons. A total of 22 improved maize hybrids and three commercial standards were tested. Out of the 22 tested, two hybrids CKPH08035 (7.4–9.9 t ha⁻¹) and CKPH08039 (7.3–9.8 t ha⁻¹) significantly out yielded the commercial standards WH505 (8.8 t ha⁻¹) and BH140 (5.5 t ha⁻¹). In addition to yield, the improved hybrids also possess desirable traits including good plant height, good plant and ear aspects and good husk cover. The hybrid CKPH08004 had the lowest Dobie index of susceptibility and was regarded as resistant to S. zeamais. Weevils fed with the resistant hybrids produced low numbers of F₁ generation weevils, had a high median developmental time and a low percentage of grain damage and grain weight loss. An increasing number of F₁ generation resulted in an increasing grain damage and grain weight loss. We found an inverse relationship between the susceptibility index and percent mortality. However, the numbers of F₁ generation, percent grain damage and grain weight loss were positively correlated with the susceptibility index. The use of resistant maize hybrids should be promoted in managing S. zeamais in stored maize under subsistence farming conditions in Africa.     

Mycoparasitic Trichoderma viride as a biocontrol agent against Fusarium oxysporum f. sp. adzuki and Pythium arrhenomanes and as a growth promoter of soybean

Trichoderma viride was proved as an effective biocontrol agent against two fungal pathogens, Fusarium oxysporum f. sp. adzuki and Pythium arrhenomanes, infecting soybean. During an in vitro biocontrol test, Trichoderma showed mycoparasitism and destructive control against the tested fungal pathogens. Both the pathogens significantly influence the germination and P. arrhenomanes had a severe effect (only 5% germination). The root system of the soybean plant was poorly developed due to the infection and it exerted a negative influence on the nodulation and further growth phases of the plant. During pot assay along with biocontrol activity, Trichoderma showed growth promoting action on the soybean plant. Trichoderma enhanced growth of shoot and root systems and fruit yield after 12 weeks of growth. Pythium and Fusarium infected plants treated with Trichoderma had ∼194% and 141% more height than pathogens alone. The fruit yield treated with Trichoderma was ∼66 per plant whereas the yield was only 41 for a control plant. The plants infected with Pythium and Fusarium and treated with Trichoderma had fruit yields of 43 and 53 respectively and those were 5 and 1.6 times higher than plants infected with pathogens.     

Factors reducing yield of organic white clover seed production in Denmark

Factors reducing yield of organic white clover seed production were investigated in Denmark. In thirty‐six fields from different regions, density of flower heads, and weevils of the genera Apion and Hypera, hatching from flower heads, were assessed. In fifteen of these fields, additional measurements were made in order to calculate potential yield and yield‐reducing factors. Flower heads had a mean of ninety‐two florets per head, of which proportionately 0·59 were intact, 0·08 were not pollinated and 0·34 damaged by weevils; 0·16 of the florets contained larvae of Apion species. In intact florets the mean number of seeds was 3·6. Density and size of flower heads were correlated with low density of flower heads leading to significantly more florets per head. The number of seeds per intact floret was correlated with the proportion of unpollinated florets. The number of insect‐damaged florets was influenced by both larvae of Apion in and the numbers of Hypera nigrirostris (Fabr.) hatched from flower heads. One larva of H. nigrirostris caused approximately ten times the damage of a larva of Apion. Densities of Apion and Hypera were influenced by location, with fields with adjacent weevil sources being most at risk. An estimate of potential seed yield showed that, even under good harvest conditions, only a small part of potential seed yield is realized and that under suboptimal harvest conditions seed loss is high. The main factors responsible for low yields in Danish organic white clover seed production were identified as unfavourable harvest conditions and weevil damage.     

Influence of phosphorus and potassium fertilization on damage to alfalfa,Medicago sativa L., by the alfalfa weevil,Hypera postica (Gyllenhall) and potato leafhopper,Empoasca fabae (Harris)

In a field study, the effects of phosphorus and potassium fertilization on damage caused by the potato leafhopper, Empoasca fabae (Harris), and alfalfa weevil, Hypera postica (Gyllenhall), to alfalfa, Medicago sativa L., were studied. Potato leafhopper and alfalfa weevil populations were either controlled with insecticides or allowed to develop as untreated controls. Insect management treatments were applied to alfalfa managed under high and low soil fertility regimes. Alfalfa grown under high soil fertility appeared more favourable for alfalfa weevil populations but was able to tolerate more defoliation. Populations of alfalfa weevil larvae were 34% higher on fertilized stands. On the other hand, potato leafhopper populations were as much as 43% higher on low-fertility stands. Alfalfa weevil damage caused a carry-over effect which reduced both plant height and yield of the second cutting. Fertilization negated this effect on height but not on yield. Stands damaged by potato leafhopper recovered more slowly after harvest, but fertilization reduced this effect. Yields from first-cutting alfalfa (which is not infested by the potato leafhopper) the following year were 10% greater on fertilized stands where leafhopper control had been applied the previous season. Plots infested by potato leafhopper suffered greater yield losses under low-fertility management. Leafhopper control and fertilization, alone and in combination with one another, negated these effects.     

Timing and extent of damage caused by insect pests of green gram (Vigna radiata L.) in Bangladesh

The occurrence and abundance of green gram pests were studied during the crop season of 1982. There were six Lepidoptera, four Coleoptera, two Hemiptera, two Orthoptera and one Diptera, of which the Lepidopteran Spilosoma obliqua Walk. was the most serious. Thysanoplusia orichalcea Fabr., Spodoptera litura Fabr. and Apogonia spp. were abundant during September and October, whereas S. obliqua and Ophiomyia phaseoli Coq. were represented most in October. Etiella zinckenella Treit. was abundant during the middle of October to the second week of November. Larvae of all instars of all six Lepidopteran pests were collected in the field, except for T. orichalcea and Manduca spp. with larvae of only the third and fifth instars. No larvae were found in the field of other orders of insect pests, except O.phaseoli and Epilachna dodecastigma Muls. The fifth- and sixth-instar larvae consumed more leaf material than did those of the first four instars. Larval damage potential in terms of leaf area consumed was greatest in Manduca spp. and lowest in Lamprosema diemenalis Guen. whereas Apogonia spp. were recorded as eating the greatest leaf area among adult Coleopteran pests. The natural enemies were also recorded in case of S. obliqua and L. diemenalis. Data on the biology of some of the insect pests are given and discussed briefly.     

Morphological traits and allocation patterns related to stress-tolerance and seed-yield in wild and domesticated evening primrose (Oenothera L. Onagraceae)

Wild evening primrose species (Oenothera spp.) native to Argentina, have been suggested as a new crop for irrigated valleys of semi-arid Patagonia. This paper describes patterns of biomass allocation, morphological traits related to stress-tolerance and seed-yield in four species of Oenothera grown in a common garden at three plant densities. Wild and domesticated species are compared. The effect of resource availability on those traits during three phenological stages (vegetative, reproductive and maturity) is described. Native species were characterized by traits related to stress-tolerance (high root allocation and low specific leaf area) during the vegetative stage. This suite of traits resulted in low biomass accumulation and low seed-yield. The domesticated O. biennis was characterized by a combination of traits related to stress-tolerance (low specific leaf area) and high productivity (high leaf allocation and leaf area ratio and low root allocation). Domesticated species accumulated more biomass than natives. Total biomass and total non-structural carbohydrates present in roots were positively correlated to seed-yield.Oenothera biennis showed the highest seed-yield, although this species showed yield instability in response to changes in the environmental quality. No changes in seed-yield in response to plant density were recorded for either O. lamarckiana or native species. Oenothera biennis showed an optimum density of 20 plants m⁻² and yielded 260 g m⁻², a seed-yield similar to that reported in other countries. Low seed-yield of native species is major drawback that must be overcome. Improving seed-yield in these species could be possible by selection oriented to increase total biomass. Since no detrimental effect of density was found in O. lamarckiana and natives, a higher plant density might increase yield production per unit area.     

Evaluation of neonicotinoids as pyrethroid alternatives for rice water weevil management in water-seeded rice

The rice water weevil (RWW), Lissorhoptrus oryzophilus (Kuschel) (Coleoptera: Curculionidae), is the most destructive insect pest of rice in the United States. Water-seeded rice, which is flooded at an earlier stage of crop development than drill-seeded rice, is at heightened risk of loss from root-feeding RWW larvae. Pyrethroids, the most widely used group of foliar insecticides for RWW control, have inherent limitations such as limited residual activity, narrow window of activity and extreme toxicity to non-target aquatic organisms. An array of field, lab and greenhouse experiments was conducted to compare the activity of two neonicotinoids with that of λ-cyhalothrin, a widely used pyrethroid, against the RWW. Small-plot efficacy trials were conducted during 2009, 2010 and 2011. Foliar clothianidin (Belay 2.13 SC) and a granular formulation (3%) of dinotefuran applied to plots were as effective as, and showed greater residual activity than, foliar applications of λ-cyhalothrin. Topical bioassays on adult weevils revealed that clothianidin possessed lower contact toxicity than λ-cyhalothrin. Residual assays using weevils placed on foliage of sprayed plots revealed that the toxic and sublethal behavioral effects of clothianidian on adult weevils were more persistent for clothianidin than for λ-cyhalothrin. Granular dinotefuran applied to greenhouse-grown plants previously infested with weevil larvae showed excellent larvicidal activity. Overall, these studies showed that neonicotinoids have potential as pyrethroid replacements against the RWW in water-seeded rice culture.