WALNUTHUSK FLY MANAGEMENT

Helmut Riedl, R. G. Hislop, V. A. Brown, J. Reilly, W. W. Barnett, W. W.Coates, R. Coviello, J. E. DeTar, J. Joos, P. McNally, W. H. Olson, R. R.Sanborn, and W. R. Schreader.

OBJECTIVE 1

adults: In our 1981 trapping experiments we sought to improve the ef-ficiency of the spherical trap through additional studies of trap color,chemical baits, and trap size and shape.

PROCEDURES (Objective 1)

Trap color: Spherical traps (dlam. 8 em) painted five different shades ofgreen were compared: light fluorescent green, dark fluorescent green,foliage green, Shamrock green and a very light green. Reflectance curveswere obtained far all colors used in this test with a Spectronlc 505spectrophotometer.

Chemical bait: In this test ammonium carbonate was added to the yellowrectangle and the green sphere. Ammoniumcarbonate (3g) was placed In aplastic vial which was open on each side and mounted In the center of eachtrap. Four trapping units were tested: green spheres and yellow rec-tangles with and without ammonium carbonate.

Trap shape and size: Three 3-dlmenslonal trap shapes and three differenttrap sizes were evaluated: a cube, a sphere, and an oval. The smallesttraps were similar In size to a walnut and within each size class thevisible area (silhouette) was the same. There was a four-fold differencein visible area between size classes. In another test the green sphericaltrap was compared to a single disc with the same diameter as the sphere,two discs arranged In a cross and a three-disc trap. All traps In thesetests were painted Shamrock green.

In all trapping experiments described here, five replicates of each traptype were used. Traps were coated with Tanglefoot and hung at eye levelsurrounded by foliage. The catch was sexed, recorded and removed twice orthree times every week. To minimize the effect of distributional dif-ferences In the husk fly population on catch, traps were rotated to anothertrap location whenever they were checked.

RESULTS (Objective 1)

Trap color: Spheres painted very light green caught significantly fewerfiles than the other shades. The fluorescent greens In this test had aconsiderably higher reflectance than Shamrock green or foliage green.However, this did not result In higher catches and except for the verylight green all other shades were equally attractive.

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Chemical bait (Table 1): Addition of ammonium carbonate considerably In-creased trapping efficiency of the yellow rectangle and the green sphere.However, ammoniumcarbonate reduced the species-specificity of the sphereand large numbers of other fl ies, mainly in the family Lauxaniidae, werecaught. We did not investigate whether ammoniumcarbonate-baited greenspheres gave similar seasonal catch curves as unbaited spheres.

Table 1.-Evaluation of baited vs. unba-ited spheres and rectangles formonitoring walnut husk fly. 1981.

Trap type

Green sphere2

Sphere + a.c.AM (ye II ow)

rectangleRectangle + a.c.

1/Means followed by a different letter are significantly different (0.05level).

Zla.c. (ammoniumcarbonate)

Trap shape and size: The round shapes, spheres and ovals, were more at-tractive than cubes (Table 2). With the spherical and oval traps we noteda definite increase in response to the larger sizes. The medium sphere ap-peared to be as efficient as the large sphere. Ovals which more closelymimic the shape of a walnut were not more attractive than spheres. The ex-periment with single and multiple disc traps was an attempt to develop amore practical alternative to the spherical trap (Table 3). The singledisc caught few fl ies, but catches Increased significantly as discs wereadded to the trap unit. The 3-dlsc trap which has a silhouette similar toa sphere regardless of the direction of approach was as effective as thesphere.

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Table 2.-Evaluatlon of traps of different

shapes and sizes for monitoring walnut husk fly.1981.

Trap type

1

Avg. husk fly catch/trap/day8/10-8/19 8/20-8/28

Large cubeMedium cubeSmall cube

2Large sphere~1edIum sphere

Sma II sphere

Large ovalMedi um ovalSma II oval

8.0ab

8 .1ab

1.2c

19.7a10.4ab

1.8c

14.3a6.9b

0.3c

7.8cd13.7b2.0e

22.0ab18.1abc3.9de

28.7a10.0bc1.4e

1/Means followed by a different letter aresignificantly different (0.05 level).

7./D ian. 16, 8, and 4 em.

Table 3.-Evaluation of green disc traps for

monitoring walnut husk fly. 1981.

Trap type

Avg. husk fly catch/trap/day8/31-9/7 9/8-9/15

SingleDouble

TripleSphere

discdiscdisc

3.918.024.410.7

1.94.612.98.4

CONCLUSIONS (Objective 1)

In research prior to this year, we determined the color preference with 2different trap shapes. Green was the most attractive color when combined

with a spherical shape, while yellow was preferred when combined with a

-ectangular shape. Addition of a chemical bait to a visual trap can vastlyImprove its trapping efficiency. For Instance, anmonium carbonate added to

The vellow rectangle increased its sensitivity several fold. By com-~artson, protein hydrolysates are poor attractants for the walnut husk fly.~he green sphere was quite selective and caught primarily walnut husk

,.,ies. Its major drawback was low trapping efficiency. Results of our

981 trapping studies to improve the sensitivity of the spherical trap sug-;~S+ that Shanrock green is as attractive as fluorescent greens with high

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reflectance, spherical traps are as attractive as walnut-shaped, ovaltraps, and catches Increase with the size of a trap. In addition, a trap

consisting of three green discs may be a more practical design than a solidspherical trap since coated discs can be easily transported in a flat

package and then assembled in the field.

OBJECTIVE 2

oviposition: As in 1980, field experiments were carried out in majorwalnut-growing areas to compare trapping efficiency of husk fly traps andto define the relationship between seasonal catch curves and oviposition.

PROCEDURE (Objective 2)

Two trap types were used in these tests: 1) fluorescent yellow rectanglecharged with a dispenser containing 3 grams of ammonium carbonate, and 2)green sphere (diam. 8 cw). Traps were coated with Bird Tanglefoot and hungat head height in the N quadrant of a tree. Five traps of each type wereused in this season-long experiment. The catch was removed and recordedonce a week. Three weeks after the first files were caught, 400 nuts (20per tree) were inspected for stings every week until the first stings werefound. After that nuts were Inspected for oviposition punctures and damageevery two weeks. Similar experiments were conducted In six differentlocations.

RESULTS (Objective 2)

Similar to results in 1980, ammonium carbonate baited rectangles were farmore sensitive than the spheres, and began to pick up files as soon as they

emerged in late June, early July. Throughout the season, the baited rec-

tangles caught significantly more files than the green spheres. The green

spheres began to catch files In August when nut damage was first noticed Inthe orchards. Catches on the green spheres were better synchronized with

oviposition (Fig. 1). The same trend was observed In all six locationswhere experiments were conducted.

CONCLUSIONS (Objective 2)

The ammonium carbonate baited yellow rectangle and the green spherical

traps may both have a place In a monitoring program for the walnut huskfly, since each trap type provides different Information. The baited rec-tangle is a much more sensitive trap and thus appears to be better suited

for survey purposes and detection of low populations. By comparison, the

sphere Is a better Indicator for oviposition and damage and thus appears tobe a more useful tool for timing of control measures against the husk fly.

In addition, research Is In progress to evaluate whether any meaningfulcorrelations can be developed between catches In the two trap types anddamage levels.

OBJECTI VE 3

A sequential sampling plan has been developed based on distributional

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studiesof ovipositionpunctures on the nut, within a tree and between

trees. We anticipate field testing of this sampling program In 1982.

OBJECTIVE 4

Varietal susceptlbl Iity: Larval development, mortality and damage to shell

and kernel In relation to time of attack on major walnut varieties.

PROCEDURE(Objective 4)

Nuts (Franquette variety) were caged weekly through the season with files

which had emerged In the laboratory. The date of oviposition was recordedand files were removed. Cages were left In place to prevent further

oviposition on a nut by feral files. Alternatively, uncaged marked nuts

were checked for oviposition several times a week. When a nut was stung Itwas caged to prevent addltlnal oviposition. Two weeks after ovlpostlon the

egg cache was removed from each nut to determine percent hatch and obtain a

base value for larval mortality. Caged nuts were checked dally for larvalemergence and the number of emerging larvae was recorded. Continuous

records of ambient temperature were obtralned with a hygrothermograph. Abattery-powered analog recorder was used for temperature measurements Inthe husk.

RESULTS (Objective 4)

Larval development: The heat unit total necessary to complete larvaldevelopment varied markedly with the time of attack. The duration of lar-

val development was longer In early season and It was strongly negativelycorrelated with nut maturity. Duration of development Is likely Influencedby food quality of the maturing husk. Egg and larval mortality: Egg mor-tality in the husk was very low through the season. However, larvalsurvival was low very early In the season and close to hull spilt. Periodsof 100°F and above for several hours also caused high larval mortality.Damage to shell and kernel: Nuts which were Infested at various timesthrough the season were bleached and dried. These samples will be sub-jected to a quality check to determine degree of shell staining, kernelmalformation, discoloration, and mold.

CONCLUSIONS (Objective 4)

Information on varietal susceptibility, and on changes In susceptibility

through the season wil I allow us to fine-tune the management program forthe walnut husk fly. From the quality analysis of husk-fly Infested nuts

we wll I be able to relate husk Infestation levels to the actual damage toshell and kernel and determine how this relationship varies through theseason. This Information Is essential In defining decision lines for thesequential sampling program (see Objective 3).

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OBJECTIVE 5

PROCEDURE(Objective 5)

In previous years we demonstrated with hydraul ic handgun applications thatbait sprays need not be appl led to the full canopy for good control ofadult husk fl ies (see article In California Agriculture 35, 9 & 10: 23-25).In 1981 we evaluated the pyrethrold fenvalerate (Pydrln) with and withoutbait appl led by speed sprayer In a ful I-scale orchard test. We comparedthe following treatments: 1) ful I coverage without bait, 2) alternate rowwith bait, 3) every third row with bait, 4) one side every row with bait,and 5) untreated check. Fenvalerate 2.4 EC was used at 0.1 lb. AI/l00 gal.and protein hydrolysate was added at 1 qt./l00 gal. Each treatment con-sisted of three 1 acre replicates. Pherocon AM traps were placed in thecenter of each repl icate. Sprays were appl led about ten days after catchesshowed a significant increase. Leaf samples were collected twice afterdate of treatment and examined for mites. At hull spilt about 40 nuts wereexamined for husk fly Injury on each of 10 trees In each replicate for atotal of 1200 nuts per treatment.

RESULTS (Objective 5)

The infestation levels In the five treatments are shown in Table 4. As Inprevious years, the pyrethroid fenvalerate without bait did not providecontrol. Applications of fenvalerate with bait to every other row or toone side in each row provided the same level of control. Both of thesetreatments required only half of the insecticide used In the full-coveragetreatment. Spraying only every third row would be even more economical,but may not provide adequate control (Table 4).

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Table 4.-Control of the walnut husk fly with fenvalerate 2.4 ECwith and

without protein hydrolysate bait at full and reduced coverage.

~/ALNUTS- ~/AUIUTHUSKFLY .l!

FULTOtl ORCHARD- SON0I-1ACOUNTY,CA. - - 1981

II. Rledl, J. L. Joos, J. t1. Johnson, R. S. ~1endes,R. G. Hislop, J. E. Aliaga

--

Materials and Rate of Application 2/and Coverage -

Total # of 3/Nuts Counted

# of NutsInfested

%-Infested

I0\V1I

Fenvalerate 2.4 EC0.1 lb./ai/100

1. Fu11 Coverage

2. Alternate RowsSprayed

3. Every Third RowSprayed-.--4. One Side, Every Row Sprayed

5. Untreated Check

1/ Rhagoletis completa Cresson

£/ Applied by speed sprayer at 250 gal ./acre on 8/9/81j treatment #2, #3, and #4with Staley's 17 bait at 1 qt./l00 gal. Treatment #1 without Staley.s #7 bait

1/ Samples taken on 10/1 and 10/5/81, from 3 replications (average 10 trees/replication)

1306 321 25

1237 79 6

1281 153 12

1159 81 7----- -

1211 374 31

CONClUSIONS (Objective5)

Tests In 1981 confirmed previous results that pyrethrolds are only effec-tive against the walnut husk fly if applied In combination with proteinhydrolysate bait. With bait, coverage can be reduced without sacrificingeffectiveness of the application. Alternate row spraying appears to be themost economicaltreatmentmethod becauseof savings In Insecticide, fueland labor. Some growers reportedly have been using alternate row sprayingwith good success against the husk fly. According to our data alternaterow spraying is indeed an effective treatment concept for the applicationof bait sprays against the walnut husk fly.

OBJECTIVE 6

nut husk fly: Basic biological studies have been carried out to developInformation on the temperature thresholds for growth of eggs and larvae andon the duration of development in the egg and larval stage as a function oftemperature. These studies are being completed and are part of a thesisproject (Valerie Brown). In addition, studies were conducted to determinefactors responsible for dlapause termination In the overwintering prepupalstage. We began to examinethe followingfactors In laboratory and fieldexperiments: duration of chi Iling below 41°F, effect of moistureandamount and seasonal distribution of rainfall.

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PUBLICATIONS

Riedl, H., and S. A. Hoying. 1981. Evaluations of trap designs and at-tractants for monitoring the walnut husk fly, Rhagoletls completaCresson (Dlptera: Tephrltldae). Z. ang. Ent. 91: 510-520.

Riedl, H. et al. 1981. New monitoring methods for the walnut husk fly.California Agriculture 35 (9 & 10): 21-22.

Hislop, R. G., H. Riedl, and J. L. Joos. 1981. Control of the walnut huskfly with pyrethrolds and bait. California Agriculture 35 (9 & 10):23-25.

Hislop, R. G., H. Riedl, and J. L. Joos. 1981.of bait sprays on walnut husk fly control.Tests 6: 46.

Effect of reduced coverageInsecticide & Acaricide

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I0\00I

.-. 100ZU.IU0::U.I0-U.I>~-J=>~::>u

JUL

000 RECTANGLE+ a.c.... SPHERE-

- - - NUT DAMAGE

AUG SEPT OCT

Fig. l.-$easonal catches (cumulative percent) with two trap types in relation to

nut damage(Cooperator: J. E. DeTar, FarmAdvisor, Solano C.).