Bruchophagus roddi (alfalfa seed chalcid)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Hosts/Species Affected
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Plant Trade
- Wood Packaging
- Impact Summary
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Bruchophagus roddi Gussakovskii, 1933
Preferred Common Name
- alfalfa seed chalcid
Other Scientific Names
- Bruchophagus gibbus medicaginis
- Eurytoma roddi Gussakovskii
- Eurytoma roddi Kolobova, 1950
International Common Names
- French: chalcis granivore de la luzerne
Local Common Names
- Australia: lucerne seed wasp
- Bulgaria: lucernov semeyad
- Germany: Luzerne Samenwespe; Samenwespe, Luzerne-
- Hungary: lucerna-magdarázs
- India: lucerne seed chalcid
- Russian Federation: lucernovaya tolstonozka
- Ukraine: lucernovae semyaed
- USA: clover seed chalcid
- Yugoslavia (Serbia and Montenegro): osica lucerkine mahine
- BRPHRO (Bruchophagus roddi)
Summary of InvasivenessTop of page The alfalfa seed wasp is a small insect (less than 2 mm long) that can be spread through flight. The larvae develop within a single alfalfa seed and they are easy to spread through the world in the seed trade. It is difficult to find all the stages. The pest only damages the seeds and where alfalfa is used in non-seed production it passes unnoticed. However, it can be found everywhere that flowering alfalfa is available: around sheds, gardens, stock yards, fence lines, irrigation channels, check banks, stock raceways, along roadsides and in grazing pastures. The seed wasp has continuing, overlapping generations, which means that all stages of the life cycle are present at any one time, in any one area and in any one paddock. A spray that is used to kill the adult will have no effect on the pupae and they will emerge immediately after the spray has been applied, and almost immediately mate and continue the life cycle. The wasp is exposed to insecticides, which are used in commercial seed production to manage other pests, for 6 months of the year through the dryland and irrigated seed production season. The resistance of the seed wasp to insecticides is commonly reported in the seed-producing areas of south Australia and New South Wales. A similar scenario exists in the alfalfa seed-producing areas of North America, where district-wide sanitation practices are encouraged. Up to 80-90% of the harvested seed may be infested and this can cause great financial losses.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Hymenoptera
- Family: Eurytomidae
- Genus: Bruchophagus
- Species: Bruchophagus roddi
Notes on Taxonomy and NomenclatureTop of page For a long time this species was identified as Bruchophagus gibbus, which damages the seeds of clover and other leguminous plants. Gussakovskii described the alfalfa seed chalcid as B. roddi (Rodd et al., 1933).
DescriptionTop of page The adult alfalfa seed chalcid is a minute, jet-black wasp. Only some parts of the legs (on the tibia and tarsus) are yellow-brown. The male is 1.2-1.7 mm and the female is 1.3-1.8 mm long. The thorax protrudes and the abdomen is egg-shaped with a plain ventral part (Grigorov, 1976; Zerova, 1995).
The egg is shiny-white, semi-transparent and oval-shaped with a long thread-like tail (Grigorov, 1976).
The fully grown larva (grub) is white, apodous, 'C'-shaped and approximately equal to the size of an alfalfa seed (1.5-2 mm) (Grigorov, 1976; Padmavathi et al., 2003).
DistributionTop of page B. roddi is closely related to its host plants and it can be found everywhere that alfalfa is grown (Grigorov, 1976). It is said to have a cosmopolitan distribution (Zerova, 1995).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|-Indian Punjab||Widespread||Prashar and Dhaliwal, 1984; CIE, 1988|
|-Uttar Pradesh||Widespread||CIE, 1988; Padmavathi et al., 2003|
|Iran||Present||Khanjani and Kalafchi, 2003; Arbab, 2006|
|Kyrgyzstan||Present||Krylova, 1982; CIE, 1988|
|South Africa||Present||CIE, 1988|
|-Canary Islands||Present||CIE, 1988|
|-Saskatchewan||Present||Soroka and Spurr, 1998|
|-Arizona||Widespread||Butler et al., 1968; CIE, 1988|
|-California||Widespread||CIE, 1988; McDaniel and Boe, 1991|
|-Iowa||Present||Small & Brookes, 1984; CIE, 1988|
|-Kansas||Present||Brewer, 1980; CIE, 1988|
|-Maryland||Present||McDaniel and Boe, 1991|
|-New York||Present||CIE, 1988|
|-Pennsylvania||Present||Wheeler, 1974; CIE, 1988|
|-South Dakota||Present||McDaniel and Boe, 1991|
|-Wisconsin||Present||McDaniel and Boe, 1991|
|Bulgaria||Widespread||Native||Not invasive||Dirimanov, 1962; CIE, 1988|
|Czechoslovakia (former)||Widespread||Kral'ovic, 1971; CIE, 1988|
|France||Widespread||CIE, 1988; Aeschlimann and Vitou, 1989|
|Hungary||Widespread||Erdélyi et al., 1979; CIE, 1988|
|Moldova||Widespread||Antonova and Bazyleva, 1974; CIE, 1988|
|Russian Federation||Present||Present based on regional distribution.|
|-Russia (Europe)||Present||CIE, 1988|
|Serbia||Widespread||Spasic et al., 1988|
|Yugoslavia (Serbia and Montenegro)||Widespread||Native||Not invasive||Spasic et al., 1988|
|-New South Wales||Widespread||Introduced||Invasive||CIE, 1988|
|-South Australia||Widespread||Introduced||Invasive||De Barro, 2001a; De Barro, 2001b; CIE, 1988|
|-Western Australia||Present||Introduced||Invasive||CIE, 1988|
|New Zealand||Present||CIE, 1988|
History of Introduction and SpreadTop of page The origin of B. roddi is probably Palearctic, the same as its food plant (Medicago sp.). The pest is already present in Africa, Asia, Australia, Oceania, Europe, North and South America.
Risk of IntroductionTop of page Strict quarantine activities can delay the spread of the pest, but they probably cannot stop invasion in all the countries where alfalfa is grown.
HabitatTop of page The wasp is an excellent parasite of alfalfa and develops its populations in response to the availability of the host rather than any particular environmental cue such as temperature or day-length. However, the wasp will hibernate (diapause) in the winter in response to cues in the autumn. Irrigated seed crops within a 5 km radius of dryland seed crops (or significant pasture or wasteland seed-producing alfalfa) are infested unless they mature within 4 weeks of the maturity date of the dryland crop. The areas outside the 5 km radius are not significantly affected regardless of the crop maturity date, especially if the crops in this region mature at a similar time. The dryland seed crops and the presence of feral and pasture lucerne in the areas near to irrigated seed crops can be hosts for population development. Research has shown that the seed wasp can be found everywhere in the presence of flowering alfalfa: around sheds, gardens, stock yards, fence lines, irrigation channels, check banks, stock raceways, along roadsides and grazing pastures (De Barro, 2001a, b).
Hosts/Species AffectedTop of page Recent research indicates that B. roddi only attacks the seeds of Medicago plants (lucerne/alfalfa). Zerova (1995) reported ten Medicago species that the pest was discovered from. The most important are Medicago sativa, Medicago falcata, Medicago glutinosa [Medicago sativa subsp. glomerata] and Medicago caerulea [Medicago sativa subsp. caerulea].
The records of the wasp in Trifolium (clover) seed are probably a mistake. Clover seeds are damaged by Bruchophagus gibbus. The larvae of both species are morphologically similar.
SymptomsTop of page The adult female of the alfalfa seed chalcid has a needle-like structure (ovipositor) that is used to insert eggs into immature alfalfa seeds. A single larva (grub) develops within each seed and destroys all the contents, leaving only the seed coat. When the wasp emerges from the seed, a hole is visible.
List of Symptoms/SignsTop of page
|Seeds / empty grains|
Biology and EcologyTop of page Physiology and Phenology
The alfalfa seed chalcid is attracted by flowering alfalfa and oviposits into immature seed in young developing pods. Once the seed starts to swell it is not susceptible to oviposition by the chalcid. This wasp requires a flat, soft pod through which to oviposit. The wasp larva requires the duration of the seed-filling period to develop into a pre-pupa and pupa, and it feeds on the seed endosperm. Once the seed ripens the pupa hatches and the wasp chews out of the seed and pod. The wasp will stay in a pre-pupal stage in the ripened seed if it is late in the season and is induced into a winter diapause.
In Australia, it is known that the wasp is more active in February than earlier in the seed crop season and that the presence of volunteer alfalfa in the area surrounding the seed crop can augment the seed wasp population. The wasp does not develop populations in defined intervals. It has continuing, overlapping generations, which means that all the stages of the life cycle are present at any one time, in any one area and in any one paddock. A spray that kills the adults will have no effect on the pupae, which will hatch straight after the spray has been applied, and almost immediately mate and continue the life cycle (De Barro, 2001a).
In Canada, Soroka and Spurr (1998) stated that seed yields and infestation levels were correlated with temperature, rain and degree-day data from the year of and the year preceding seed collection. The infestation level of B. roddi was most closely correlated with the temperature and rainfall in July and August of both years. The proportion of damaged seed is highest in the years following warm and dry summers. Alfalfa cultivar also influences the infestation levels; winter-hardy cultivars that become dormant early in the autumn have lower levels of chalcid-damaged seeds than less hardy cultivars that maintain growth later in the season.
Kral'ovic (1971) established that in south-west Slovakia the adult females lived longer than the males and those that fed, lived longer than those that did not. The thermal optimum for the adults was 18-20°C and the ratio of males to females was approximately 1:1. Seeds that were approximately 10-days-old were the most satisfactory for oviposition. Temperatures of 20.2-27.7°C and 30 or 60% saturation of the soil are optimal for pupation. Sub-zero temperatures are important for the larvae of the over-wintering generation, where a period of intense cold increases their vitality. In warm years, peak numbers of adults are present in mid-June, but in cool ones the peak occurs later. The first generation of larvae does not enter diapause, but larvae of the second (autumn) generation remain in diapause for 80.64 days (on average) at 23°C and 99 days at 18°C.
Diapause in B. roddi is one of the principal mechanisms for the survival and perpetuation of this multivoltine species in alfalfa seed. The chalcid diapauses in the pre-pupal stage. Diapause begins on approximately 1 September and is completed on approximately 1 December, when 100% of the population is in diapause. The day-length for induction ranges from 10.5-13 h; only approximately 40% of the population diapauses at a day-length of 10.25-11 h. Diapause lasts for approximately 5.5 months, from 1 December to 15 April. Termination of the diapause and emergence of the population occur over a period of approximately 2 months, from 15 April to 15 June. A day-length of 13-14.5 h terminates diapause (Nielson, 1976). A small number of adults emerged in the second year (1984) from seeds collected in the autumn of 1982 (Thoenes and Moffett, 1987b).
There is an olfactory orientation towards the host plants. The females of B. roddi exposed to crude extracts of seed pods of both red clover and alfalfa responded positively by orientating towards extracts of alfalfa pods but not red clover pods. Bruchophagus gibbus responded to extracts of red clover pods but not alfalfa pods. Both species responded to extracts of both red clover and alfalfa flowers (Kamm and Buttery, 1986). Little knowledge on the chemical communication of those herbivore species is available. Oct-1-en-3-ol, (E)-2-hexenal, (E)-2-hexen-1-ol, (Z)-2-hexen-1-ol, (Z)-3-hexen-1-yl acetate, (E)-beta-farnesene and caryophyllene released from the host plants affected the host finding and ovipositional behaviour of the two sibling alfalfa and clover seed wasps, B. roddi and B. gibbus (Mazomenos and Krokos, 2000).
B. roddi develops two generations per year in most of the countries where it occurs. It is possible to have one or three generations depending on the ecological conditions.
In Europe, B. roddi usually has two generations per year, which last about 2.5 months from approximately the middle of June to September, but in long warm summers there may be a third. It over-winters as fully grown larvae (pre-pupae) and pupates in the spring. The adults emerge by making a small round hole through the testa and the pod during flowering and pod formation in May to June (10-12 days after pupation) and copulate. The females insert single eggs into the developing seed through the green pods and continue until the end of their life. The oviposition period is approximately 35-42 days. One female lays from 15 to 65 eggs in the green pods. The larvae hatch after 9 days at 19-22°C and 6 days at 23-27°C. They develop within a single seed (feeding within the endosperm) of the first cut. This takes approximately 18-20 days at 23-27°C and 25 days at 19-22°C. They pupate in this seed and the pupal stage lasts for 7 days at 22-25°C. It takes approximately 1 month to complete one generation. The emergence of the adults of the first generation, which are more numerous, takes place between mid-July and the end of August, during the flowering of the second crop. The second and third generations develop in the seeds of the second and third cut. Since the regions vary widely in climate, in some colder areas only one generation may develop per year (Kral'ovic, 1971; Antonova and Bazyleva, 1974; Grigorov, 1976; Nielson, 1976; Gulii and Pamuzak, 1992).
Observations on the adults of B. roddi in Oklahoma, USA from mid-May until the end of September show that maximal population densities generally occur in August. The adults emerge earlier at lower elevations and at more southern locations than at higher elevations or at the most northern location. The males emerge earlier and in greater numbers than the females, until early June. Thereafter, more females emerge. Overall, 60% of the emerging adults are female. The females in the alfalfa fields outnumber the males by ratios of 1.5:1 to 2:1. Peaks of adult emergence in different fields range from three to six per year. The chalcid infests alfalfa seed throughout the growing season, with an infestation rate of 3.7% in June, increasing to 38.6% in August. Diapausing chalcids are found in nearly every sample, and the percentage in diapause ranges from 0 in June to 81.9 in August (Thoenes and Moffett, 1990a, b).
In Jhansi, Uttar Pradesh, India, the pest completes two generations in a season and over-winters as a pupa (from the second generation) inside the seed. The adults from the over-wintered pupae emerge in late-March during pod initiation. The developing grub feeds on the internal contents of the seed, leaving the outer shell and pupates there. Grub development takes place in 3-4 weeks, coinciding with the seed-filling period (Padmavathi et al., 2003).
In Montana, USA there may be several generations in a summer. Over-wintering occurs in the larval stage, inside the seed, with emergence occurring late in the following spring (Whitmer et al., 2003).
The presence of continuing, overlapping generations is probably the reason for the six generations per year announced in Ludhiana, Punjab, India (Prashar and Dhaliwal, 1984).
The seed wasp can be found everywhere in the presence of flowering alfalfa; around sheds, gardens, stock yards, fence lines, irrigation channels and check banks as well as in stock raceways, along roadsides and in grazing pastures (De Barro, 2001b).
The development rates of B. roddi do not significantly differ when the larvae develop on different alfalfa clones. A variation in field infestations is probably dependent on the factors affecting oviposition. Temperature, day-length and resource competition affect the field infestation levels and they are associated with diapause. Larval diapause appears to be induced in the female parent (Brewer and Horber, 1984).
The examination of pod samples taken from 30 microplots in an alfalfa stand grown for seed at Kompolt, Hungary, in 1977 revealed that the percentage damage caused by B. roddi and Tychius flavus was 47 and 15, respectively. However, the two species often occurred in the same pods and the presence of seeds infested by B. roddi and also chewed by T. flavus indicated that there was competition between them. There was a close reciprocal correlation between the damage caused by both pests. A detailed examination of nine of the samples indicated that pod size was related to oviposition preference. B. roddi and T. flavus caused maximum damage to pods containing four and six seeds, respectively. The proportion of pods infested by B. roddi increased rapidly up to three-seeded pods but remained unchanged in larger ones, whereas the proportion of pods infested by T. flavus increased continuously. The number of seeds damaged by both pests also increased with the number of seeds per pod (Erdelyi et al., 1979).
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
Notes on Natural EnemiesTop of page Some significant natural enemies of the alfalfa seed chalcid are reported. All of them are larval parasitoids from the order Hymenoptera.
In the Rostov region of the former USSR, Artokhin (1983) reported five species of larval parasites of the alfalfa seed chalcid. Up to 93% of the pest larvae were parasitized. The dominant species are Pteromalus sequester and Baryscapus bruchophagi, which cause 33 and 31% parasitism, respectively. Two had three generations per year and their flight began earlier than that of the host. Idiomacromerus perplexus parasitized up to 18% of the larvae; it has two generations per year and its flight begins at the end of the flight period of the first generation of the host.
In France, the entomophagous complex associated with B. roddi comprises 12 species of Hymenoptera, of which only P. sequester significantly contributes to a reduction in the eurytomid populations. As a consequence, it is suggested that this pteromalid can be given a strong priority for an attempt at the biological control of B. roddi on Medicago spp. in south-eastern Australia (Aeschlimann and Vitou, 1989).
In Oklahoma, USA, Thoenes and Moffett (1987a) collected five hymenopterous parasitoids of the alfalfa seed chalcid. Over 99% of the parasitoids were either I. perplexus (90.4%) or B. bruchophagi. The other three species were Eupelmus allynii, Idiomacromerus insuetus and Lyrcus maculatus. Most parasitoid emergence occurred from early June to mid-July, the actual time depended on parasitoid species and where the seeds had been collected. Emergence peaks of the parasitoids followed those of the pest by 1 to 2 weeks. Small numbers of I. perplexus and B. bruchophagi emerged in the second year (1984) from seeds that were collected in the autumn of 1982.
De Barro (2001a, b) in Australia named two species of parasitic wasps that were collected from the reared wasps. I. perplexus and P. sequester hatched in late November at a ratio of 2:1 females to males. These wasps were collected from offal from across the district, providing evidence that they are widespread but in low populations. They have also been detected in Forbes and Deniliquin in New South Wales. According to the author, very little is known about the biology of these wasp parasites but they are worth investigating as a biological control option.
Szocs et al. (1998) from Hungary suggested a simple method for separating beneficial parasitoids (B. bruchophagi, I. perplexus and Pteromalus medicaginis) of the alfalfa seed chalcid from alfalfa chaff.
Means of Movement and DispersalTop of page B. roddi spreads by adult flight (in restricted areas) and infested seeds.
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|True seeds (inc. grain)||larvae; pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|Growing medium accompanying plants|
|Stems (above ground)/Shoots/Trunks/Branches|
Wood PackagingTop of page
|Wood Packaging not known to carry the pest in trade/transport|
|Loose wood packing material|
|Processed or treated wood|
|Solid wood packing material with bark|
|Solid wood packing material without bark|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page A survey by questionnaire of 18 European countries showed that the four main pests of alfalfa seed production, in decreasing order of importance, were the cecidomyiid Contarinia medicaginis, the mirids Adelphocoris lineolatus and Lygus rugulipennis, and the eurytomid B. roddi, which affected the plant from flowering until pod setting (Bournoville et al., 1984).
B. roddi is a seed pest of alfalfa (Medicago sp.) and causes 5-83% seed loss (Kolobova, 1950), and Bruchophagus kolobovae and Bruchophagus gibbus attack Lotus sp. and Medicago sp. seeds (Fabaceae) (Gates, 2001).
In Russia, Gulii and Pamuzak (1992) announced 25-40% yield losses and in Montana, USA up to 80% of the seed harvested in September may be infested (Whitmer et al., 2003).
Research indicates an average total of irrigated seed loss of 67.39 kg/ha. A value of A$3/kg to the producer equates to a financial loss of A$202.16/ha. Approximately 9700 ha of irrigated seed production in south-east Australia is susceptible to infestation by the seed wasp. Losses to producers in the area are approximately A$2 million per season. In 1999/2000, a total of 4993 tonnes of alfalfa seed at a value of A$3.63/kg was exported, equating to a value in excess of A$18.2 million. A$5.18 million of potential seed exports are lost due to the alfalfa seed chalcid (De Barro, 2001a, b).
In Jhansi, Uttar Pradesh, India, the chalcid damage resulted in an economic loss of Rs. 12,000/ha in 2001-2002 and Rs. 9300/ha in 2000-2001 (Padmavathi et al., 2003).
Detection and InspectionTop of page A sweep net should be swept through the alfalfa and the contents inspected. The seed wasp will be present in the net if any are in the field (De Barro, 2001b).
Kral'ovic (1971) suggested a method for forecasting the extent of infestation. The intensity of attack to be expected in a given area in a given year can be estimated from the sum of the effective temperatures (degree-days) in the previous year.
The infested seeds can be discovered before the emergence of the adult by attempting to sink them in a 15-20% salt solution. The infested seeds are lighter in weight and will rise to the surface (Dirimanov, 1962).
Similarities to Other Species/ConditionsTop of page Many small wasps and flies that exist in an alfalfa seed crop can be confused with the alfalfa seed chalcid. Most of the small wasps are good predators of aphids and Heliothis spp. and have long tail-like features (ovipositors), which the seed wasps lack. Many small flies such as midges are common in alfalfa, especially in irrigated crops. These midges are most often misidentified as seed wasps because they are the same size and shape. However, midges do not have a shiny jet-black abdomen but have a dull, grey-white one. The other feature that makes them distinct to the untrained eye is that the midge flies away quickly when captured, whereas a seed wasp tends to curl up and 'play dead'. The midge also flies around people and animals on warm, humid days. The seed wasp keeps at a distance from people (De Barro, 2001b).
B. roddi is similar to Bruchophagus gibbus and Bruchophagus kolobovae, and the most useful difference between them is the male genitalia (Strong, 1962; McDaniel and Boe, 1991), the shape of the abdomen and other morphological features (Zerova, 1995). This pest differs from the other two Bruchophagus species that damage seeds of Medicago plants (Bruchophagus medicaginis and Bruchophagus evolans) by the shorter marginal vein and lighter wings than B. evolans. (Fedoseeva, 1958; Zerova, 1995).
Prevention and ControlTop of page
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.
Research indicates that eradication of the seed wasp is not possible. Insecticide application is not a means of permanent control. The wasp will always be present where alfalfa is grown and the key to management is to live with the presence of the pest but make changes to the management in order to reduce its impact on seed yield (De Barro, 2001b).
Cultural Control and Sanitary Methods
Cultural practices are important in managing this pest. In the spring, the cultivation of the soil using a disc cultivator and irrigation kills infested seeds on the soil surface. Clipping-back established stands helps to delay bloom, provides a shorter pollination window and reduces the time that the green pods are available for egg laying. The elimination of volunteer alfalfa along roadsides and ditch banks is also important in minimizing seed chalcid populations (Peterson, 2003).
Seed wasps develop populations where alfalfa is flowering and setting seed. Sanitation practices such as mowing, grazing and herbicide spraying significantly reduce the presence of the wasps in the seed crops by reducing the availability of the alfalfa outside the seed crop for population development. Australian alfalfa seed producers can individually and in co-operation with the adjacent landowners/seed producers, implement simple sanitation practices on a wide scale level to reduce seed wasp populations and damages to the seed crops.
Research has shown that by reducing the presence of flowering alfalfa around sheds, gardens, stock yards, fence lines, irrigation channels, check banks, stock raceways, along roadsides and in grazing pastures, the presence of the seed wasp in seed crops is reduced. The best results are obtained by maintaining those sanitation efforts from the time that the alfalfa first flowers through to when the seed crops have finished flowering. In practice this may require a combination of grazing, spraying and mowing two or three times in a single season.
Many Australian seed producers stop the seed production of alfalfa in December so that the crops flower in January and February when the warm/hot weather is optimal for pollination. However, this management strategy permits maximum wasp damage. The producers need to assess their management concepts. By closing a crop 2-4 weeks earlier than usual (e.g. in November), harvesting at 100% ripeness is permitted as opposed to 80-90% ripeness, later in the season and prior to the autumn rainfall. Seed wasp damage is reduced by earlier crop closure due to lower wasp populations being present at the time of flowering and seed set. The net return from a seed crop that is closed in the traditional December period is often the same or less than the net return from a similar standard seed crop that is closed earlier. In December, the crop is not permitted to reach complete ripeness prior to desiccation, whereas the crop that is closed earlier reaches full ripeness and has less seed wasp damage.
In combination with alterations in crop closure timing, both sanitation and closing date operate synergistically to diminish seed wasp populations. With a sanitation and closing date management programme in operation, the population of seed wasp in the area will decline over a period of seasons. Seed producers need to assess the economics of management decisions that influence the susceptibility of seed crops to seed wasp damage in conjunction with net returns (De Barro, 2001b).
Those methods can be applied anywhere according to the seasons and development of alfalfa.
Various border stands alongside alfalfa were investigated in southern Hungary in 1992-1994. In 1992, fennel, maize and Pimpinella anisum were established in border stands. In 1993, fennel, hemp and Coriandrum sativum were tested. In 1994, fennel and hemp were tested. The low incidence of B. roddi (and Tychius flavus) was barely sufficient to assess the effects of border plants on the damage they caused (Erdelyi et al., 1995).
After careful observation of all the developmental stages of B. roddi, Tingely and Nelson (1975) showed that ovipositional non-preference was the only resistance mechanism operating.
Laboratory trials of 11 clones drawn from Medicago sativa, Medicago sativa subsp. praefalcata and Medicago glandulosa [Medicago sativa subsp. falcata] revealed significant differences in infestation by B. roddi. It is suggested that clones with glandular-haired and tightly-coiled pods are resistant. The incidence of black or brown oviposition marks on developing seeds has been negatively correlated with the resistance assessed by field evaluation (Brewer et al., 1983).
In Oklahoma, USA, Springer et al. (1990) compared pod-wall characteristics with seed damage and resistance to the alfalfa seed chalcid in Medicago species. The findings suggested that pod-wall lignification may reduce seed losses due to chalcid damage. The highest levels of resistance to the eurytomid are found in the annual species, which also had highly lignified pod-walls.
Aeschlimann and Vitou (1989) studied natural enemies in Mediterranean France with a view to finding agents for introduction into Australia. They concluded that Pteromalus sequester was the only significant natural enemy in France and recommended its introduction into Australia.
It is important that the control programme for the seed chalcid starts in the spring, as this species cannot be controlled by insecticide applications during the production of the seed crop. The adult wasp inserts eggs inside the pods, and the larval and pupal stages develop inside the alfalfa seeds. The pest over-winters as pupae in the seeds that were spilled in the previous season or in seeds that were produced by the alfalfa grown in field border areas and roadsides. The adults emerging in May and June lay eggs in the alfalfa seeds wherever they are available, with the most common seed source being the plants growing outside of the fields. Several generations of the chalcid are completed each year, with the levels of seed infestation becoming progressively higher as the chalcid populations increase in mid- and late summer. That is why the insecticide treatment has to be directed against the adults before oviposition. The next application is when it is necessary. Two treatments, one applied at budding and the other at the green-pod stage, reduce the percentage of infested seeds and almost double the yield (Ivanov and Medvedev, 1970; Grigorov, 1976; Whitmer et al., 2003).
The suggested contact insecticides depend on the year of use: dimethoate and chlorinated 2,6,6-trimethylbicyclo [3.1.1]hept-2-ene and diazinon (Sapunaru and Paulian, 1971); 0.1% fenitrothion, 0.2% tetrachlorvinphos, 0.2% trichlorphon, 0.2% carbaryl, 0.2% phenthoate and 0.2% diazinon (Antonova and Bazyleva, 1974); phosolone, kelevan, gamma-BHC and fenitrothion (Mateias et al., 1977); phoxim, etrimfos and pirimiphos-methyl (Deordiev, 1982); cypermethrin (Holtkamp and Horwood, 1991); alpha-cypermethrin and deltamethrin (Sapunaru et al., 1998); esfenvalerate and fipronil (Sapunaru et al., 2000).
Phosalone and a few other insecticides are not highly toxic to pollinators, therefore these are used when the alfalfa is in flower. The first cutting of alfalfa should not be used for seed production. Seed from the second cutting is less damaged by pests and can be protected well by the insecticides tested (Stokovskaya et al., 1977).
According to De Barro (2001a), chemical control of the seed wasp is not a viable or sensible option and does not form part of its management strategy. The wasp is exposed for 6 months of the year (through the dryland and irrigated seed production season) to insecticides that are used in commercial seed production to manage other pests. Resistance of the seed wasp to insecticides including malathion, chlorpyrifos, and a range of synthetic pyrethroids is commonly reported in the seed-producing areas of South Australia and New South Wales. A similar scenario exists in the alfalfa seed-producing areas of North America, where district-wide sanitation practices are encouraged.
In California, USA, when the fields are divided into two groups (based on the number of insecticide applications: one to two applications versus three to five applications), there are 2.3 times more chalcid-damaged seeds found in the three to five insecticide application group, compared to the one to two application group. Increased insecticide applications may reduce the predator and parasitoid populations that would normally suppress the seed chalcid populations (Peterson, 2003).
Field Monitoring/Economic Threshold Levels
The economic thresholds of phytophagous insects in seed alfalfa in the Rostov region of the former USSR were calculated in 1979-1982 using a mathematical formula. In the early-harvested crop, the threshold abundance per square metre was 15-20 B. roddi adults and in the late crop, it was 15-20 B. roddi adults (Artokhin, 1984).
ReferencesTop of page
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