Rice water weevil

Table of content

Introduction of the Insect
Classification
Distribution and Status
Identification
Problems with Identical signs
Habit and Habitat
Life cycle (Bionomics)
Damage
Common signs and symptoms of infestation
Symptoms of damage
Why is it important?
Management
Cultural practices
Biological control
Chemical treatment
Restrictions
Genome sequences
Published research.
References

Introduction of the Insect

Lissorhoptrus oryzophilus is an insect belonging to the order Coleoptera. It is native to North America, mostly in the southeastern part of the country, but has been established in California for over 50 years. A separate species of rice water weevil, Lissorhoptrus brevirostris is present in Cuba, Dominican Republic, Colombia, Suriname and Venezuela. Lissorhoptrus oryzophilus began spreading through the rice growing regions of Asia in 1976 (China, India, Japan, Korea and Taiwan); in Europe it has been present in Italy since 2004, in the regions of the Piedmont and Lombardy where it affects upland rice production [1]. Adult weevils are small (1/8 inch), grayish-black snout beetles which may have a darker brown V-shaped area on their backs.

English name Rice water weevil

Bangla name [NO INFORMATION AVAILABLE]

Scientific name Lissorhoptrus oryzophilus

Classification

Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Curculionidae
Genus: Lissorhoptrus
Species: Lissorhoptrus oryzophilus
Binomial Name: Lissorhoptrus oryzophilus (Kuschel, 1951)

Distribution and Status

L. oryzophilus is indigenous to North America and occurs in Canada, USA and Mexico (Kuschel, 1951). It was accidentally introduced into Japan on infested rice straw in 1976 (Tsuzuki and Isogawa, 1976; Hirao, 1978). The distribution range of this pest has expanded to mainland China (Nagata, 1990) and Korea Republic in 1988 (Hirao, 1988; Way, 1992) and Taiwan (Shih, 1991; Shih and Cheng, 1992) and Korea DPR in 1990 (Way, 1992).

Host Range
It is a parasite on monocotyledonous plants such as Poaceae and Cyperaceae. Rice fields in non-native areas. Primarily aquatic grasses and sedges (see lists below); larvae attack roots, whereas adults attack leaves.Rice is the economically significant host plant in the USA, Japan, Korea DPR, Korea Republic, Taiwan and China. The host range of L. oryzophilus in Japan includes 76 monocot plants in 56 genera and seven families (Kisimoto, 1992) and in Korea Republic includes 29 plant species in three families (Shih and Cheng, 1992).In addition to rice, which is its primary host, L. oryzophilus attacks the following wild, secondary hosts:USA: Agrotis avenacea, Axonopus compressus, Cynodon dactylon, Cyperus flavicornis, Echinochloa crus-galli var. zelayensis, Echinochloa crus-galli, Eleocharis obtusa, Eleocharis palustris, Jussica suffruticosa, Panicum dichotomiflorum, Panicum hians, Paspalum larranagae, Paspalum plicatulum, Paspalum bascianum, Paspalum dissectum, Paspalum urvellei, Polypogon monspeliensis, Scirpus mucronatus and Setaria geniculata.Japan: Eragrostis ferruginea, Imperata cylindrica, Leersia oryzoides, Miscanthus sinensis, Pennisetum japonicus, Phragmitis communis and Pleioblastus variegatus.Taiwan: Alopecurus aequalis var. amurensis, Bambusa multiplex, Commelina communis, Cynodon dactylon, Cyperus cotundus, Cyperus difformis, Cyperus iria, Cyperus serotinus, Digitaria clumbens, Echinochloa crus-galli var. formosensis, Echinochloa crus-galli var. oryzicola, Eleusine indica, Eragrostis japonica, Imperata cylindrica, Kyllinga brevifolia, Leersia hexandra, Miscanthus floridulus, Miscanthus sinensis, Panicum repens, Paspalum distichum, Paspalum thunbergii, Poa annua, Rhynchelytrum repens and Setaria viridis. It also attacks sugarcane and maize.

The most common host plants include Alopecurus aequalis (Dent foxtail), Axonopus compressus (carpet grass), Cynodon dactylon (Bermuda grass), Cyperus difformis (small-flowered nutsedge), Cyperus iria (rice flatsedge), Cyperus serotinus, Echinochloa crus-galli (barnyard grass), Imperata cylindrica (cogon grass), Leersia hexandra (southern cut grass), Leersia oryzoides (Rice cutgrass), Oryza sativa (rice), Panicum repens (torpedo grass), Poa annua (annual meadowgrass), Poaceae (grasses), Saccharum officinarum (sugarcane), and Zea mays (maize).

Identification

Egg: White; cylindrical and elongate, 0.8 mm long by 0.2 mm wide, length three to five times greater than the width; oviposited in submerged leaf sheaths on the lower half of the rice plant

Larva: White, legless grubs; presence of paired curved dorsal tracheal hooks on the second through seventh abdominal segments, apical segment of the hook is sclerotized and used to pierce root tissue and sequester oxygen, basal segment of the hook is tubular and flexible and separated from the trachea by chitinized rings; four larval instars with head capsule widths varying in size from 0.16 mm to 4.5 mm; body lengths of 1.5 mm (first-instar larvae) to 8 mm (fourth-instar larvae). Larvae were described by Lee and Morimoto (1988).

Prepupal stage: Mature fourth-instar larvae form a mud cocoon in a prepupal stage (1-2 days), with the cocoon attached to the root.

Pupa: White; formed in an oval, water-tight mud cell attached to plant roots; resembles the adult in size and shape.

Adult: Dark-brown to black with grey scales; small, oblong (2.8 mm long by 1.2-1.8 mm wide); in sexually dimorphic weevils, the female is more robust than the male and the first two ventral abdominal sternites are flat to convex at the midline of the female, whereas they are broadly concave in the male; females have a large darkened area on the elytra and a deep notch in the seventh tergal segment.

Problems with Identical signs

Kuschel (1951) found that Lissorhoptrus simplex comprised two closely related species; he retained Lissorhoptrus simplex for one species and described the other, the common rice water weevil, as Lissorhoptrus oryzophilus. The two species are separated on the basis of hind tibiae characters of males and the form of the male genitalia.

Habit and Habitat

Rice water weevils go through 1 generation in Japan and California, but in parts of southern China and the southern US they will undergo up to 3-4 generations per year. The adults feed on leaves and the sheath leaving diagnostic feeding scars which can help gauge the severity of an infestation. The adults will lay eggs beginning in March through May depending on the latitude. The larvae feed on the roots, which is the cause of yield reduction in rice. The loss of roots reduces the number of plant tillers, which are the panicle bearing structures of the rice plant. Reduction in tillering leads directly to yield loss. In case of strong infestations yield losses can reach 30%.
The adult undergoes diapause during the winter from November through March at the foot of perennial grasses or under vegetative cover. When the temperatures overcome the 21 °C, they migrate toward the rice fields either by crawling off levies or flying into fields. Adults are most active in the late afternoon or evening when temperatures are higher than 26 °C and wind speeds are less than 5 mph.
L. oryzophilus is spread by parthenogenesis, flying, swimming and hitchhiking on human transportation (Chen et al., 2005).
Adults are semi-aquatic and can be found on or beneath the soil surface. Perennial grasses and sedges that are common in or near rice fields serve as alternative host plants for adult weevils. Both male and female adults of L. oryzophilus occur in the south-eastern states of the USA (Arkansas, Louisiana, Texas), but only parthenogenetic females occur in Japan, Korea Republic and Korea DPR, Taiwan and California (USA). Ovarian development of L. oryzophilus has been classified into six grades: 0 – no oocyte; I – pre-vitellogenic; II – gravid; III – ovipositing; IV – late ovipositing; V – post oviposition) (China).

Life cycle (Bionomics)

Females lay their eggs (2.3-3.7 eggs per female per day) in submerged leaf sheaths, with up to 106 (Japan) to 239 (USA) eggs laid per female. Eggs hatch in 6-10 days, depending on the temperature. Newly hatched larvae feed for a short period of time before crawling down the plant to the roots. Four larval instars are completed in 28-37 days. Mature fourth-instar larvae form a mud cocoon in a prepupal stage (1-2 days), with the cocoon attached to the root. Adults emerge in 5-7 days and either prepare to overwinter or, in areas where there are two generations per year, to re-infest rice. In double-cropping rice areas of China, adequate food supply impacted summer diapause of first generation adults rather than air and soil temperature or daylength. The density of L. oryzophilus in second crop rice is lower than in the first crop.
The pearly white eggs are cylindrical (0.8 mm long and 0.14 mm long) of pearly with a very thin corion. The eggs are laid in the leaf sheath and sometimes in the roots. Larvae hatch from eggs after 4–9 days.
The larvae are aquatic and live their entire lives in the rhizosphere. They are white and grow up to 1 cm long at 4th instar stage. The larvae survive in the anoxic zone by using modified spiracles that are shaped as dorsal hooks connected to the tracheal system. These hooks penetrate into the aerenchyma cells of rice plants and other wetland grasses for respiration.[2] The larvae go through 4 instars (or stadia) and complete development in about 28–35 days. The pupae is a small silk cocoon encased in mud (0.5-0.9 cm long) and attached to the roots. The pupal stage takes around 7 days to complete.
The adults are 3.3-3.7 mm long, including the rostrum. The exoskeleton ranges in color from dark beige, brown, or dark-brown. Along the center of the elytra, some rice water weevils have an elongated dark brown to brownish-black mark. The middle pair of legs have hydrophobic hairs that allow it to swim (Hix et al. 2000).

Damage

Many countries and economies where this insect occurs as a non native treat it as invasive, having a major impact on rice production fairly rapidly after introduction. Given the large expanses of some areas dedicated to rice production, the insect is predisposed to be invasive in characteristic. Primary damage includes root pruning by larvae which causes stunting and chlorosis of seedling plants and lodging.
L. oryzophilus causes serious losses to rice yields throughout its geographic range. In the USA, yield reductions on infested acreage range from 10% in Arkansas to 33% in California. L. oryzophilus has spread throughout the Japan archipelago since its introduction in 1976, with yield losses of 41 to 60%. From 1988 to 1992, it has occupied more than 50% of the total rice acreage in Korea Republic and has been predicted to spread throughout all of the rice-growing areas in Korea Republic.

Common signs and symptoms of infestation

Adults rasp the leaf epidermis of rice leaves, leaving skeletonized, longitudinal, slit-like scars on the upper leaf surface. LarvaRoot pruning by larvae causes stunting and chlorosis of seedling plants and lodging, a delay in maturity and yield reduction in mature plants.

Symptoms of damage

Plants/Leaves/abnormal colours
Plants/Leaves/external feeding
Plants/Roots/external feeding
Plants/Roots/reduced root system

Why is it important?

[NO INFORMATION AVAILABLE]

Management

Rice water weevils can be monitored by examining field edges for leaf scarring. Adult populations can be estimated using floating barrier traps. The best way to quantify populations of rice water weevil that can be directly related to yield losses is through soil coring (Way and Espino 2014).
Managing rice water weevil depends on the region and its ecology. In the Southern US, growers use drill seeded systems that allow them to delay planting or flooding of the rice fields. This allows rice plants to grow larger and better tolerate rice water weevils. Southern rice growers also use seed treatments with thiomethoxam (Cruiser) that also help In California, the best methods are treating field edges, rebuilding levees, winter flooding, and foliar spraying with pyrethroids such as lambda-cyhalothrin (Warrior) or neonicotinoids such as clothianidin (Belay). The spraying of insecticides is the cheapest option available to growers.
Host plant resistance has been investigated in rice but results have been less than desirable. Since the 1960s, out of 10,000 lines tested, only 2 showed moderate resistance to rice water weevil feeding. Unfortunately the 2 lines had poor agronomic traits, which led to their discontinued use [1]

Cultural practices

Early attempts to control L. oryzophilus in Asia and the US involved the removal or drainage of rice fields to reduce larval populations. This strategy has been effective and controlled larval feeding damage under specific field conditions; however, it can be impractical because of loss of fertilizer, and is also ineffective when rice is reflooded too soon or if rain occurs during the time when fields are drained. Delaying the establishment of permanent flood (2 to 3 weeks later than normal) in the USA avoids problems associated with draining and reflooding. L. oryzophilus populations are reduced and delayed, and noxious weed management improved without herbicide inputs. Planting rice early (before mid-April) in Louisiana (USA) did not avoid the build-up of damaging L. oryzophilus larval populations, but early-planted rice was able to tolerate infestations without yield loss. Stout et al. (2000) provided evidence for the utility of early planting and delayed flooding for management of rice water weevil in Louisiana (USA). In Asia, there have been efforts to destroy sites where adults overwinter by removing the top layer of soil and associated vegetation near paddy fields. This control tactic is neither feasible nor effective.

Biological control

Infection of overwintering L. oryzophilus adults (14.8-32.7% infection rate) by Beauveria bassiana has been observed in Taiwan. There has been interest in using the entomophagous fungi B. bassiana and Metarhizium anisopliae as microbial control agents for L. oryzophilus in Japan. Although adults were highly infected with the fungi, the density of the first-generation larvae and pupae were not reduced because there were high populations and because infected adults oviposited before dying; L. oryzophilus populations were not reduced sufficiently using either fungus. Overwintering L. oryzophilus populations in Taiwan are reduced using B. bassiana and M. anisopliae, but reduction differs based on density of adults and timing of fungal conidia application. The application of M. anisopliae at the pre-oviposition stage reduced the adult population of L. oryzophilus by 92.5% 13 days after spraying in China (Chen et al., 2000). Larval and adult populations in the coming generation also decreased. A mermithid nematode has been associated with mortality and reduced fecundity in adult females in Arkansas (USA), but its efficacy for population control is not known.

HOST PLANT RESISTANCE
Research efforts in Taiwan and the USA have attempted to locate sources of resistance to L. oryzophilus in rice lines and cultivars, because all cultivars currently grown are susceptible to damage caused by larval feeding. In Taiwan, over 200 lines and cultivars have been screened for larval resistance, with 37 lines of Hshinchu 64 identified with high levels of resistance (absence of larvae and pupae). In the USA, more than 8000 USDA Rice World Collection lines have been screened for larval resistance. Six lines were identified with moderate resistance and five lines identified with low resistance. Recently, Anther culture, tissue culture and breeding lines identified with resistance to larval L. oryzophilus were categorized for tolerance, antixenosis and antibiosis. The anther culture lines (95-2836 and 95-3527), Louisiana breeding lines (8720906 and 8721937), tissue culture lines (112 and 4754) and other breeding lines (AL6029, LA2218, TX22041, URN199 and URN200) were identified with moderate levels of tolerance to damage caused by larval feeding. These lines supported high larval populations, but yields did not decline or were higher when compared with paired treated controls. These lines also recovered from root-pruning damage caused by larval feeding. Additionally, two tissue culture lines (244 and 2232), three Louisiana breeding lines (8723417, 8723518 and 8825454) and two Texas breeding lines (TX12685 and TX13079) were identified with antixenosis.

NATURAL ENEMIES
L. oryzophilus has no known parasitoid natural enemies. A mermithid nematode has been found to cause mortality and reduction of egg production in adult females in Arkansas (USA), but its impact on suppressing rice water weevil populations is unknown. Predation on adult rice water weevils by Hyla cinerea, Hyla squirella and Rana pipiens has been observed, while larval rice water weevils have been preyed on by the immature Libellulid dragonfly nymph Pantala flavescens in the USA. Typical natural enemies include: Beauveria bassiana (white muscardine fungus), Hirsutella jonesii, Hyla cinerea (American green treefrog), Hyla squirella (squirrel treefrog), Metarhizium anisopliae (green muscardine fungus), Pantala flavescens, and Rana pipiens.

Chemical treatment

In the USA, there has been heavy reliance on insecticides as the major control method against L. oryzophilus. Numerous insecticide products have been screened since the 1960s, but most were phytotoxic to seedlings or interacted with herbicides causing seedling damage. In Asia, most research to control L. oryzophilus has emphasized chemical control as a major control tactic. For example, in 1992, Korea DPR used the synthetic pyrethroid etofenprox after transplanting as the only control tactic for the weevil. Japan has over 30 insecticides registered for control of L. oryzophilus, with carbosulfan, benfuracarb, cycloprothrin, etofenprox and cartap used in recent years. Cycloprothrin, fenthion and pyridaphenthion-fenobucarb are registered as foliar sprays; cycloprothrin and etofenprox-fenobucarb are registered as granular applications; and carbosulfan and ethofenprox-fenobucarb are registered as seedling box applications in Korea. In Taiwan and the USA, carbofuran granular applications are effective insecticides against L. oryzophilus, but in the USA registration for use of carbofuran to control larval populations ended in 1995. In a study of the effects of alternative insecticides, Lambda-cyhalothrin, diflubenzuron and fipronil were found to be more effective than carbofuran [a hazardous chemical that is not recommended] at preventing early larval infestation of rice roots, but less effective at preventing later infestation of roots (Stout et al., 2000). Yields from plots treated with the three insecticides were generally higher than those treated with carbofuran, probably because prevention of early injury to roots had a more beneficial impact than prevention of later injury.
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product’s label.
IPM Programmes
There has been heavy reliance on insecticides in Asia and the USA to control L. oryzophilus below economic thresholds. This may destroy natural enemies and pose a threat to non-target organisms and the environment. Different control tactics need to be combined to suppress L. oryzophilus populations below a damaging threshold and to develop effective integrated pest management (IPM) programmes for this pest. Control tactics that have been evaluated include cultural manipulation using field drainage, biological control using entomophagous pathogens, host-plant resistance and chemical control.

Restrictions

[NO INFORMATION AVAILABLE]

Genome sequences

[NO INFORMATION AVAILABLE]

Published research

https://academic.oup.com/ee/article/51/1/108/6433307

https://www.jstage.jst.go.jp/article/aez/40/1/40_1_31/_article

https://link.springer.com/chapter/10.1007/978-94-024-0948-2_9

https://pubmed.ncbi.nlm.nih.gov/35171281/

https://www.sciencedirect.com/science/article/abs/pii/S0261219405000037

https://bioone.org/journals/journal-of-agricultural-and-urban-entomology/volume-35/issue-1/1523-5475-35.1.36/First-Report-of-Rice-Water-Weevil-Lissorhoptrus-oryzophilus-in-Grain/10.3954/1523-5475-35.1.36.short

https://repository.lsu.edu/cgi/viewcontent.cgi?article=2884&context=gradschool_dissertations