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Research Project Report
California Melon Research Board
for the period of January 1, 2005 to December 31, 2005
Carbamate Baits for Soil Dwelling Insects on Melon Crops
PRINCIPAL
INVESTIGATOR: Eric T. Natwick
University of California Cooperative Extension - Imperial County
COOPERATING
PERSONNEL:

LOCATION:

OBJECTIVES:
The immediate objectives are to assess the efficacy of insecticide baits and timing of their
placement to protect cantaloupe melons from soil dwelling insect pests.
ABSTRACT:
Nine insecticide baits and a control were evaluated for efficacy against darkling ground beetles
(DGB), Blapstinus spp., in cantaloupe at Holtville, CA. Randomized complete block design field
plots, with four replicates, measured 15.25m X 8.13m. Insecticide baits were applied at 2 week
intervals in May and June. Baits included 2-Gowan Co. products, 5% carbaryl bran bait and
0.5% permethrin grape pumas bait; 2-Wilber Ellis Co. products, 5% carbaryl bran pellets and 5%
carbaryl bran crumbles; 2-DuPont products; 0.22% indoxacarb corn grit granules and 0.045%
indoxacarb corn grit granules; and 4 baits formulated by USDA-ARS-NCAUR consisting of pre-
gelatinized corn flour granules with 20% montmorillonite clay and cantaloupe rind juice baits
with 5% carbaryl, 1% imidacloprid, 5% spinosad, or no insecticide, respectively. Beetle
populations in field plots were evaluated via 2 methods. First, numbers of beetles beneath 20
melons per plot were recorded. Second, beetles beneath 10 potato slices, 6.35mm thick, per plot
were recorded after12h. Laboratory experiments consisted of choice tests, evaluating
attractiveness, and no-choice tests evaluating toxicity. All insecticide bait entries controlled DGB
in the field study. In the no-choice laboratory experiment, the 0.5% permethrin grape pumice bait
treatment had the most rapid knock-down and highest mortality, followed by 5% carbaryl bran
bait. In the choice tests, DuPont 0.22% indoxacarb, Advion (0.045% indoxacarb) and USDA
corn flour bait formulations were among the most attractive to DGB. Addition of 10% sugar, 5%
vegetable oil or a combination of sugar and oil made the USDA corn flour bait more attractive to
DGB. A comparison of the 4 formulations of pre-gelatinized corn flour granules, showed that
bait with insecticide were no less attractive than blank corn flour bait.
INTRODUCTION:
Darkling ground beetles (DGB), Blapstinus spp., are pests of cantaloupe melons in the desert
southwest, USA. They congregate beneath fruit when they begin to ripen and feed on the net and
may bore into the flesh of the melon, Fig. 1. Insecticide baits have long been used to control this
pest through broadcast application just prior to and during fruit ripening.
Fig. 1. Darkling ground beetles and damage to cantaloupe. Imperial County, CA is a major melon producing areas in the low deserts of the southwestern US. In 2002, there were 12,685 acres of melons; 10,629 acres of cantaloupe, 1,101 acres of honeydew and misc. melons, and 955 acres of watermelons in Imperial County, which had a combined gross value of over $53.8 million. In 2003 there were 12,626 acres of melons in Imperial County including 10,042 acres of cantaloupe, 1,466 acres of honeydew and misc. melons, and 1,118 acres of watermelons in Imperial County, which had a combined gross value of over $44.3 million (2003 Imperial County Agricultural Crop and Livestock Report). Failure to control these pests reduced the quantity and quality of fruit harvested. Alternatives to carbamate baits used against darkling beetles needs to be identified and registered for use in melon fields in California. Several insecticides are now available for insect pest control in melons, but many uses of older insecticides are being limited or lost to melon growers as the agricultural chemical industry struggles to meet Food Quality Protection Act (FQPA) target for risk cup allowances for organophosphate, carbamate and pyrethroid chemicals. There is resistance in the agricultural chemical industry to develop, register and market insecticide baits. Insecticide baits containing carbamate insecticides (methomyl or carbaryl) or pyrethroid insecticides have been used historically for control of soil dwelling pests such as darkling beetle earwigs and sowbugs. Alternative insect pest control insecticides need to be identified and registered for use in California to replace carbamate baits for control of soil dwelling insect pest such as darkling ground beetle and earwigs. Proper timing and application of insecticide baits needs to be investigated to maximize control of soil dwelling insect pests in melon crops. Our goal is to identify insecticides acceptable to US EPA to replace chemicals targeted by the FQPA and provide information needed for registration of new insecticides for control of soil dwelling insect pest, such as darkling beetles, on melon crops in California. PROCEDURES:
Cantaloupe Field Study
Esteem cantaloupe were planted on March 17, 2005 at the University of California Desert
Research and Extension Center near Holtville, CA. Nine insecticide baits applied on May 11, 26
& June 6 for comparison to the untreated control in a randomized complete block experiment
with four replicates. Darkling ground beetles counted on 20 fruit per plot on June 10,15 and 22
and counted on potato piece (Fig. 2) placed in plots on June 7, 10 and 15. Melon harvest data
were collected on June 16, 20 and 24.
Fig. 2. Potato slice used in DGB bait efficacy evaluation.
Treatments are listed below:
Gowan Ambush 0.5% permethrin bait (grape pumas)
Gowan Sevin 5% bait (bran)
Wilber Ellis Sevin 5% bait (pellets)
Wilber Ellis Sevin 5% bait (crumbles)
DuPont Indoxacarb 0.22% bran bait
TN-Advion Fire Ant Bait 0.045% indoxacarb
Carbaryl 5% corn flour granule bait (USDA-ARS-NCAUR)
Imidacloprid 1% corn flour granule bait (USDA-ARS-NCAUR)
Spinosad 5% corn flour granule bait (USDA-ARS-NCAUR)
Untreated Control
Laboratory Studies
Several laboratory studies were conducted including some or all of the aforementioned
treatments, corn flour granule bait with 10% sugar, corn flour granule bait with 5% vegetable oil,
corn flour granule bait with 10% sugar and 5% vegetable oil, blank corn flour granule bait.
No-choice test
No-choice tests were carried out in 5.5” diameter Petri dishes with damp filter paper in a
randomized complete block experiment with 8 replicates; 10 beetles per Petri dish in each
replicate and 0.1 grams bait per petri dish, Fig. 3. Darkling ground beetle mortality was assessed
at 1, 2, 3, 4, 5, 6, 7, 8 and 24 hours of exposure.
Fig. 3. No-choice test for bait efficacy against DGB.
Choice test (arena)
An arena choice test was conducted using 11” diameter bowls with untreated soil from melon
field. Pitfall traps (1” deep x 7/8” diameter plastic vials) were arranged in a circular pattern
within the arenas and 0.2 grams of each bait were placed in the vial in a randomized complete
block with 8 replicates. In the center of each arena, 100 live DGB were released. The DGB
numbers were recorded at 1, 2, 3, 4, and 24 hr after release, Fig. 4.

Fig. 4. Arena choice test for bait attractiveness to DGB
Choice test (chambers)
A chamber choice test was conducted using a 13.5” x 2” channel in front of nine parallel
chambers with ¾” holes leading to 2.25” x 1.125” chambers in which 0.2 grams bait was placed
in a randomized complete block with 8 replicates, Fig. 5. Along each channel, 100 live DGB
were evenly distributed. The DGB numbers were recorded at 1, 2, 3, 4, and 24 hr after release.
Fig. 5. Chamber choice test for bait attractiveness to DGB
Choice test (paired)
Paired choice tests with 13.5 x 1.75” channels with damp filter paper at each end which received
0.2 grams of the baits to be compared Each individual experiment was replicated 4 times with
100 DGB per replicate placed equidistance between the baits tested. The number of beetles per
side recorded at 1 hour after release (center 1/3 not counted), Fig 6. Percentages of DGB found at
each end calculated providing each bait 32 replicates, regardless of competing bait, to analyze for
ranking.
Fig. 6. Paired comparison arena for insecticide bait testing

Attractiveness of insecticide baits compared to blank bait paired test
Paired choice tests were performed in the aforementioned manner. The USDA-ARS corn flour
baits containing the insecticides Carbaryl, Spinosad, and Imidacloprid baits were compared to
blank bait (same bait matrix with no active ingredient).
Addition of sugar and/or oil of increase the attractiveness of blank bait paired test
Paired choice tests were performed in the aforementioned manner.Blank bait was compared to
the same bait matrix with addition of sugar and/or oil.
Field Study & No-Choice Test Results Summary
All commercially available and experimental insecticide baits reduced DGB infestations in
melons, Tables 1. All commercial and experimental baits except Sevin 5% Pellets reduced DGB
damage to melons, Table 1.
The quickest knock down in the no-choice test was as follows: Ambush > Sevin Bran >
Imidacloprid > others, Fig7. The highest percentage mortality in the no-choice test was as
follows: Ambush > Sevin Bran = Indoxacarb > Imidacloprid = Advion > others, Fig. 7.
Table 1. Insecticide Bait Efficacy Against Darkling Ground Beetles In Melon, Holtville, CA
z PTM is the post treatment mean. Means within columns followed by the same letter are not significantly different, LSD P#0.05. Fig. 7. No-choice test results.
Arena & Chamber Choice Test Summary
In the arena choice test, bait attractiveness was as follows: Indoxacarb > Blank > Sevin Bran >
others, Fig. 8. In the chamber choice test, bait attractiveness follows: Imidacloprid = Indoxacarb
= Carbaryl flour > Advion > Spinosad > others, Fig 9. All flour bait formulations were more
attractive that registered commercial formulation except Advion. Among commercial baits,
attractiveness follows: Advion > Sevin Bran > Sevin Crumbles = Ambush > Pellets.
DuPont 0.22% Indoxacarb is not a registered bait formulation.
Fig. 8. Arena choice test.
Fig. 9. Chamber choice test.
Paired Comparisons Results Summary
The percentages of DGB attracted to a bait, at 1 hour after release were as follows: Indoxacarb
bait and Carbaryl flour were more attractive (P < 0.05) that all other formulations except
Imidacloprid flour and Advion, Fig. 8. Sevin Pellets were less attractive (P < 0.05) than all other
baits except Sevin Bran. In paired comparisons, Indoxacarb bait was more attractive (P < 0.05)
than all commercial baits except Advion and Ambush bait (grape pumas). Carbaryl Flour was
more attractive (P < 0.05) than all commercial baits except Advion and Sevin Crumbles.
Fig. 10. Percent of beetles, regardless of competing treatment, at 1 hour after release.
Paired Comparisons for Insecticide Repellency and Comparisons for added Attractiveness
with Sugar or Oil Summary
Carbaryl, Spinosad, and Imidacloprid flour formulations each attracted fewer DGB than the
blank flour bait, but the differences were not significant at P=0.05, Fig. 11. The 10% sugar, 5%
oil and a combination of each were more attractive (P < 0.05) to DGB when added to USDA-
ARS corn flour bait that blank flour bait, Fig. 12.

Fig. 11. Ground beetle attractiveness of blank bait compared to baits with active
ingredients.


Fig. 12. Ground beetle attractiveness of blank bait compared to blank bait with sugar
and/or oil added.
Conclusion
Currently registered insecticide baits for melons all control DGB. DuPont 0.22% Indoxacarb bait
and Advion (0.045% Indoxacarb) Fire Ant Bait contain oil and are more attractive to DGB than
commercial formulations of 5% Sevin and 0.5% Ambush baits. USDA-ARS flour bait
formulations are more attractive to DGB than Currently registered insecticide baits for melons.
Addition of the insecticides Spinosad, Imidacloprid, or Carbaryl to USDA-ARS flour bait does
not decrease attractiveness of the formulations. Addition of 10% sugar, 5% oil, or a combination
of sugar and oil increases attractiveness of USDA-ARS flour bait to DGB.

Acknowledgments
We wish to express our sincere thanks to the California Melon Research Board for funding this
research project. We also express our thanks to DuPont Agriculture & Nutrition and to Gowan
for their support of this project.

Source: http://www.cmrb.org/documents/files/20060105100007.pdf