Troop 324 General Camping Checklist

Biological Control of the Mexican Bean Beetle Epilachna varivestis (Coleoptera: Coccinellidae) Using the Parasitic Wasp Pediobius foveolatus (Hymenoptera: Eulophidae)

2006


Mexican bean beetle larvae P. foveolatus on larva
Prepared by: George Robbins Wayne Hudson Thomas Dorsey Thomas Scudder Mark Mayer







Phillip Alampi Beneficial Insect Laboratory
Division of Plant Industry www.state.nj.us/agriculture/plant/biolab.htm SCOPE AND COVERAGE

In 2006, the Mexican bean beetle (MBB) Epilachna varivestis (Coleoptera: Coccinellidae)
biological control program involved 30 growers with 55 nurse plots. This was a decrease of 9 plots from 2005. Planting began on May 2 with the last plot planted on May 22, well before the
Memorial Day target date. This insures that the snap beans germinate in sufficient time to attract
the overwintering MBB adults. All nurse plots were treated at planting with the preemergence
herbicides Pursuit and Dual at Rutgers recommended rates.

MATERIALS AND METHODS: Nurse Plots and Releases

One-eighth acre nurse plots were planted in areas adjacent to soybean fields with a mixture of 15
lbs. of snap beans and 5 lbs. of soybeans before the growers plant (Figure 1). The snap beans
germinate first and attract any overwintering MBB adults in the area to the nurse plot (Figure 2).
The only available food source for the MBB at that time is the snap beans with the beetles
preferring to feed on snap beans versus soybeans. Once the snap beans are consumed, the later germinating soybeans keep the beetles in the plot and out of the farmer's field. The New Jersey
Department of Agriculture, Phillip Alampi Beneficial Insect Laboratory (PABIL) uses the nurse
plot system as a trap crop to lure in the MBB (Figure 3) and keep them in the plot. The
parasitoid Pediobius foveolatus (Hymenoptera: Eulophidae) is released into the plot and the
early releases allow for rapid buildup of parasites within the nurse plots. Although P. foveolatus
females prefer third and fourth instar larvae, they attack all instars or larval stages of the
Mexican bean beetle and oviposit an average of 25 eggs within each larva. The parasitized
larvae eventually die, forming dark brown "mummies" (Figure 4). P. foveolatus is a gregarious
parasite with an average of 25 wasps, of which approximately 75% are female, emerging from
each mummy. The emerging wasps attack all larval stages in the nurse plot and continue to
search for and parasitize any healthy MBB larvae, which may have dispersed from the nurse plot
into the farmer's adjacent soybean field.
Figure 1. Planting nurse plot Figure 2. Nurse plot
P. foveolatus releases are based on initial egg sighting (egg release) and larval counts (trigger
release). Since 1985 egg releases have consisted of a total of 6,000 parasites with the first
release of 3,000 P. foveolatus made at the first observation of a Mexican bean beetle (MBB) egg
cluster. The second egg release of 3,000 parasites is made two to three days later; trigger
releases began when larvae were first observed. The initial trigger release was divided into two
releases, two to three days apart. If the MBB larval count increased seven days after the initial
trigger release, then a second single trigger release was made. Table 1 shows the decision table
developed by the NJDA.
1 Release decisions were based on monitoring the nurse plots two times per week; the sampling
unit within each plot consisted of 125 plants with 25 plants examined in each of five locations
where MBB feeding is observed.

Beginning in 2000, some releases of P. foveolatus were released in the form of parasitized
Mexican bean beetle larvae or mummies versus adults. For example, if 2,000 parasites were
required for a nurse plot, an equivalent of 80 mummies were released in 3x 6 x 1.75 paper
bags with holes large enough for P. foveolatus to emerge, twist tied to the bean plant (Figure 5).
There is an average of 25 parasites developing per mummy so the equivalent number of parasites
was released. This change in procedure allowed the PABIL to increase efficiency and to release
the requisite number of parasites using fewer laboratory man-hours. No loss of efficacy was
noted in the field. The paper bags are left in the field and do not have to be collected and
returned to the laboratory.

In 2006 release procedures were further modified due to a 50% cut in summer staff. Egg
releases consisted of one release of 4,000 parasites in the form of mummies instead, of 2
releases of 3,000. Trigger release methodology remained the same but the number of surveys
was reduced from twice a weekly to weekly after the egg releases had taken place. This reduced
the amount of time field staff was in the plots.

Figure 3. Mexican bean beetle adult Figure 4. Parasitized larva (mummy)

Figure 5. Release bag in beans and mummies
All bags/containers are kept cool in insulated Styrofoam containers (bio-mailers) with blue ice
until the parasites are ready to be released.

Direct field releases are made into other fields using surplus adult parasites that were not needed
in the nurse plots.


2 RESULTS AND DISCUSSION

Mexican Bean Beetle Levels, Parasites Released And Parasitism

The peak percent parasitism in the nurse plots averaged 11.0% (Table 2). In nurse plots where
releases were made, only 21.8% of the nurse plots required egg releases as compared to 20.3% of
the plots last year. Trigger releases were required in 38.2% of the plots versus 42.2% of the
plots in 2005. A total of 174,000 parasites were released into the nurse plots with an average of
3,010 per plot. MBB populations developed in 60% of the nurse plots compared to 62.5 %,
64.5%, 38.1%, 77%, and 76.4%, for the five preceding years (Tables 2 and 3). Releases were
made in 33 of the 55 nurse plots (Table 2).

Historically, from the time the program was implemented in 1980, until 1991, Cumberland
County had the greatest MBB pressure; however in 1991 Salem County developed the highest
populations and continued to have the highest populations until 1997. From 1998 to 2004
Monmouth County had the highest MBB populations while in 2005, Burlington County had the
highest populations. In 2006, Cumberland County had the highest levels of Mexican bean beetle
in 2006 and there was one hot spot near Port Norris where adult Mexican bean beetle got into the
growers field. The population there did not cause economic damage, however.

In 2006 there was a slight decrease in activity in all of the counties, as compared to 2005. The
MBB population continues to remain at low levels overall when one looks at the number of
Pediobius foveolatus released (Table 2). The data indicate that the populations of MBB remain
at a lowered carrying capacity due to the release of P. foveolatus. Essentially this means that the maximum MBB population that the environment will support is reduced from what it would be if
the P. foveolatus were not released.

The percentage of plots requiring releases in 2006 slightly decreased statewide.

No participating grower had to spray for Mexican bean beetle control nor was there any
need for preventive applications to any of the nurse plots.

E. varivestis Population Levels

Figure 5 shows the "host peak" (a measure of the Mexican Bean Beetle population in the nurse
plots) and the number of hosts parasitized in the nurse plots over time. The number of parasites
released in the nurse plots follows the E. varivestis population fluctuations where more P.
foveolatus are released in years of greater bean beetle pressure and less in years with reduced
populations. There have been fluctuations in E. varivestis numbers since 1981 and the number
of P. foveolatus released has followed this cycle. Insect populations are cyclical and the MBB
population shown in Figure 5 is no exception. The key observation about Figure 5 is that the
peak population of the MBB in the 90's is half of what it was in the 80's and the present
populations are one fourth of what they were in the 1980s. This trend has continued and the
MBB population is currently held at a maintenance level as a direct result of the NJDAs MBB
program.
3 4 The anecdotal evidence from observations by the field staff supports the idea that the
overwintering populations are reduced in areas where nurse plots are present but MBB
population hot spots still occur. The hot spots are located in areas where nurse plots have not
been planted for a few seasons or if there is migration from other states. The evidence is that all
counties but Salem have not had seriously high MBB populations since the mid-1980's. Salem's
increase was possibly due to flights of MBB from neighboring states and the fact that some
growers retired from farming and left the program. The nurse plots on their property were not
replaced until some years later. The increase in MBB populations in 1990 to 1993 in Figure 5 is
almost all due to Salem County. Monmouth Countys numbers are higher over the past several
years but are not due to migrations from other states as they were for the increases in Salem.
Figure 5 also shows that the MBB population levels are not as high since 2000 as they were in
the 1990's or 1980s. This is evidence that the releases by the PABIL have decreased the MBB
population in the state. The peak populations are no longer as high as the past. Dively (1985)
stated that the MBB population levels are more dependent on weather and the biology of the
insect rather than P. foveolatus and that the MBB possesses great potential to bounce back
within three years as was seen in the Battlefield area of Monmouth County where a hot-spot
developed. The release of P. foveolatus has kept the MBB population below economic levels and
as long as the MBB program is continued, growers in New Jersey should not experience serious
problems with the MBB.

Figure 5. Mexican bean beetle Population and Parasitism 1981-2006 0 50 100 150 200 250 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 Year Nu mb er o f
M BB avg.MBB pk
#MBB paras.
Parasitism data is dependent on the scouts finding mummies; if mummies are on bean leaves
that have abscised and fallen to the ground, the mummies are more difficult to find.
Therefore, parasitism data is underrepresented and the parasitism is probably greater than
what is shown in Figure 5 and in Tables 2 and 3.



Direct Field Releases
5 In 2006, as in past years, field releases of surplus parasites were made to keep additional
pressure on the MBB population (Table 4). Direct field releases are made in mid to late
season wherever MBB are observed and consist of parasites that have not been used in the
nurse plot program. Field releases are made directly into soybean, snap bean and lima bean
fields throughout Central and Southern New Jersey. In 2006, there were 24 direct field
releases totaling 252,000 parasites. The bulk of the releases were made in Salem County
where 114,000 parasites were released, followed by Cumberland with 76,000. Including the
number of parasites released in the nurse plots, a total of 426,000 parasites were released
statewide. The number of parasites released in direct field releases depends on the number of
P. foveolatus available and is not linked to a decision table. The purpose of the field releases
is threefold: 1) to suppress the MBB in areas where it could attain high population levels and
2) to reduce the over wintering population of MBB 3) to reduce the P. foveolatus storage
stocks in the laboratory. There is no correlation between the MBB population and the number
of surplus parasites released.

Using P. foveolatus has resulted in substantial savings to the growers in reduced insecticide
costs since 1981.

SUMMARY AND CONCLUSION

Overall this was a successful year MBB the populations have continued to decrease in all
counties. Parasitism levels have increased, this season; there is no evidence of MBB
populations returning to the levels observed in the past.

A portion of the soybean check-off funds reserved for research has been allocated to the
NJDA and is used to offset some of the costs for field implementation of the biological
control program. In New Jersey, populations of bean beetles are kept below economically
damaging levels in areas where there are nurse plots but also protect other soybean and bean
fields in the area due to parasite dispersal. Additionally, there is no economic impact on the
growers from the more damaging second-generation MBB population. Even though a grower
may not have any nurse plots adjacent to his fields, that grower still benefits because the plots
are carefully positioned so that the majority of the bean producing areas in the state are
protected by the parasites.

E. varivestis has the potential to bounce back and become a problem again, however it can
be kept from economically damaging levels as long as the Phillip Alampi Beneficial Insect
Laboratory can maintain its highly effective nurse plot monitoring and parasite release
program.



2007 PLANS

Plans for the upcoming season are to keep parasite pressure on developing MBB populations
by maintaining maintenance numbers of Nurse Plots throughout the counties with Mexican
bean beetle populations. The number of plots statewide will remain between 55-60 due to the
overall decline in the MBB population. If the MBB populations increase in the future, the 6 number of plots will be increased in those areas of higher MBB levels. The Port Norris area
of Cumberland County is one such area. Mummy releases worked well and will continue in
2007.

TABLE 1. Pediobius foveolatus DECISION TABLE DEVELOPED BY NJDA Pediobius foveolatus Parasite Release Decision Table First Trigger Second Trigger Peak Larval Count 1 Total Pediobius Release (Adults) #Adults #Screens/bags #Adults #Screens/bag s 1-150 2,000 2000 2 151-225 4,000 2000 2 2000 2
226-300 10,000 6000 6 4000 4
301-375 14,000 8000 8 6000 6
376-450 18,000 10000 10 8000 8
451-525 22,000 12000 12 10000 10 526+ 26,000 14000 14 12000 12 1 Total number of all larvae (1 st 4 th instars) in 125-plant nurse plot sample.
(40 mummies; approx. 1,000 P. foveolatus adults) per paper bag. 7 TABLE 2. NURSE PLOT SUMMARY BY COUNTY 2006 Average No. No. of Percent of No. of No. of Total No. of P. foveolatus Plots with Plots with Average Plots with Plots with Total No. of Parasites Released P. foveolatus P. foveolatus Percent Egg Releases Trigger County of Plots Released per Plot Releases Releases Parasitism Only Releases BURLINGTON 4 10,000 2500 2 50.0 5.7 0 2 CUMBERLAND 17 68,000 4000 11 64.7 11.4 3 8 GLOUCESTER 7 20,000 2857 5 71.4 10.9 3 2 MERCER 2 6,000 3000 1 50.0 5 0 1 MONMOUTH 8 24,000 3000 4 50.0 12.6 1 3 SALEM 17 46,000 2705 10 58.8 8.9 5 5 TOTAL 55 174,000 33 57.5 12 21 AVG. LEVELS 3010 11


TABLE 3. NURSE PLOT SUMMARY BY YEAR Year Total No. of Plots Total No. of Parasites Released Average No. of P. foveolatus Released per Plot No. of Plots with P. foveolatus Releases Percent of Plots with P. foveolatus Releases Average Percent Parasitism No. of Plots with Egg Releases Only No. of Plots with Trigger Releases 2006 55 174,000 3010 33 57.5 11 12 21 2005 64 275,000 4588 40 62.5 3.8 13 27 2004 62 252,000 3475 40 64.5 11.4 23 16 2003 84 216,000 2156 32 38.1 10.2 20 12 2002 96 544,000 5975 74 77 20.6 39 35 2001 89 578,000 7009 68 76.4 49.4 21 47 2000 90 520,000 5778 64 69 26.4 16 47 1999 96 710,000 7395 80 83.3 25.1 34 46 1998 108 680,000 6296 79 73.1 22.9 19 60 1997 113 834,000 7381 98 86.7 41.7 29 69 1996 109 670,000 6204 79 72 11.2 24 49 1995 120 828,000 6900 86 71.6 35.2 17 57 1994 120 850,000 7083 72 60 17.2 22 27 1993 111 1,101,600 9924 99 89.2 28.9 26 41 1992 112 1,272,000 11357 106 95 36.9 39 25 1991 100 1,000,000 10000 84 84 22.8 23 31 1990 106 628,000 5925 70 66 17.7 16 9 1989 130 424,000 3240 63 48.1 33.8 54 8 1988 118 682,000 8883 76 64.4 14.2 62 10 1987 117 1,260,000 10125 110 94.0 28.7 39 64 1986 117 1,541,000 9487 108 92.3 17.1 49 32 1985 111 1,156,500 9973 32.3 1984 108 633,000 6806 27.1 1983 139 975,000 8705 37.1 8

TABLE 4. SUMMARY OF ALL RELEASES IN 2006 FIELD RELEASES NURSE PLOT RELEASES
County #Field Releases #P. foveolatus Released Number of Nurse Plots #P. foveolatus Released in Nurse Plots Total #P. foveolatus Released Atlantic 1 10,000 10,000 Burlington 4 10,000 10,000 Cape May 10 114,000 114,000 Cumberland 7 76,000 17 68,000 144,000 Gloucester 7 20,000 20,000 Mercer 2 6,000 6,000 Monmouth 8 24,000 24,000 Morris 1 4,000 4,000 Salem 5 48,000 17 46,000 94,000 TOTAL 24 252,000 55 174,000 426,000
Total Parasites Released Statewide including nurse plots= 426,000




REFERENCES

1985. Dively, G.P. Mexican Bean Beetle Biological control Demonstration Project: 1980-1983. Conducted By The State Departments of Agriculture in Delaware, Maryland, New Jersey, and Virginia in Cooperation with the USDA-APHIS-PPQ National Biological Control Program.

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