Daane, Kent M

Hagen, Kenneth S. :

Rasmussen, Yvonne

Yokota, Glenn

Zheng, Yuwei :

Augmentative releases of green lacewings suppressed variegated grape leafhopper in experimental plots and commercial vineyards ; however , effectivenessvaried greatly . Field studies show that improved release methods and a of lacewing better understanding biology are needed to optimize commercial release programs . . ? f D 5 . - - y " X 0 7 Natural lacewing populationsare impor - tant becauseeach adult can lay over 1,000 eggs . of leafhopper control varies Effectiveness with lacewing release methods Kent M . Daane P Glenn Y . Yokota P Yvonne D . Rasmussen P Yuwei Zheng S . Hagen Kenneth The variegated grape leafhopper , leafhopper nymphs during its 10 - day Erythroneura variabilis , has been the pri - development period . The potentiale - scale seemsencouraging ; however , larg mary insectpest in SanJoaquin Valley grape vineyards for the past mdecade.age lacewing release programs for control - Leafhoppernymphs and adults da ling leafhoppers have produced nmixedes the leavesby feeding , which reduces results . Growersneed better guideli photosynthesis , and the fruit by excret - for these programs than are currently available . ing honeydew , which leads to sooty mold growth . Also , the flyipg adults are In our experiments , we examined the a nuisance to workers at harvest and re - effectiveness of lacewingreleases in duce their productivity . To control leaf - grape vineyards and , based upon the hoppers , most grape growers rely on field data , we can now suggest improve - pesticide treatments ; however , thesecon - ments to commercialprograms . treatments can disrupt the natural Experimental plot trials trol of spider mites and mealybugs , and there has been some leafhopper resis - To determine the field effectiveness tance to commonly used insecticides . of lacewingsas leafhopper predators , a series of small - plotexperimentswere To improve natural control , some grape growers are using augmentative releases of green lacewings , Chrysoperla species , and have reported a reduction with a cimel - hair bruih . Previous work or complete elimination of pesticide ap - plicationsfor leafhoppers . Our ' labora - had shown that releases of larvae , rather than tory studies show that lacewingsare in - eggs , provided greater control of deed voraciouspredators of the the release number due to the variability variegated leafhopper , with each larva in egg hatch and survivorship . Leafhop - consuming an average of per densities were determined every 252.4large 2 CALIFORNIA AGRICULTURE , NOVEMBER - DECEMBER 1993 19 Lacewing eggs were mixed with corn grit and placed in 5 - gallon containers . By adjust - of the container , the release rate could be controlled . ing the funnel size at the bottom Treatmentswere establishedin a ran - weeks from nymphal counts on 10 ( 1990 In 1991 , four treatments were set up : domized block design . and 1991 ) and 20 ( 1992 ) leaves per plot . 1 ) no release ; 2 ) 24 lacewingsper plot , In For each release treatment , the equiva - 1991 , two treatments were set up : with release timed by calendar date ; 3 ) 1 ) no release and 2 ) a machine release of lent number of lacewingsper acre is 24 lacewingsper plot , with a â?? synchro - lacewingeggs mixed with corn grit . In nized release given in table 1 . - timed at 50 % to 70 % In 1990 , lacewingswere released into leafhopper egg hatch to match the re - 1992 , a hand release of lacewinglarvae , cages that enclosed one - quarter of a leased lacewingswith the small leafhop - at the same rate as the machine release vine . The cages were set in a random - of lacewingeggs , was added as a third pers - and 4 ) 48 lacewingsper plot , In both years , lacewings were treatment . ized block design , with three treatments : with a synchronizedrelease . released at approximately 1 ) no release , 2 ) 6 lacewingsper cage 3,500 per acre , In 1992 , we set up two treatments in in one and two releases in the first and and 18 lacewing ? per cage . Releases 1 ) no release the first leafhopper brood : second leafhopper broods , respectively , were made accordingto a â?쳌 calendar - and 2 ) 48 lacewingsper plot , with a cal - totaling approximately 10,500 C . carnea date â?쳌 schedule.Most growers release endar - date release . In the secondbrood , per acre . Releases were made on a calen - lacewingsat peak leafhopper density , we tested possible differences among estimating that period to be near June dar - date schedule.Leafhopper densities 1 lacewing species , in four treatments : 1 ) were monitored with biweekly nymphal and July - 15for the first and second leaf - no release , 2 ) 48 C . carneu per plot , 3 ) 48 counts on C . Comanche per plot and 4 ) 48 C . 20 leaves from the center 30 hopper broods , respectively , in the San our releases vines in each plot . Joaquin Valley . We made rufilabris per plot , each with a synchro - accordingly , with slight adjustments to nized release . Releasemethod trials match lacewingdelivery and vineyard Commercialvineyard trials In vineyards , the most common management practices . lacewingrelease method is to mix lace - The study was repeated in 1991 and To test the effectiveness of lacewings wing eggs with a medium , such as cornn 150 - in commercialrelease programs , 1992 in three - vine plots . Each plot was grit , vermiculiteor rice hulls , and the vine plots were establishedin three isolated by pruning border vines spread the mixture over the vines . In the Thompson seedlessvineyards . The vine - throughout the seadon and coveringthe vineyards monitored , lacewingeggs yards were mature exposed wire trellis with a barrier of ( > 10 years ) and hadrai - were combined with corn grit , and athein - similarcultural practices ( pruned for Tanglefoot , which effectivelyprevented mixture was placed in 5 - gallon cont sins , no cover crops , furrow ) irrigation , . lacewinglarvae and leafhopper nymphs ers , which were mounted on a platform and standard application of fertilizer from moving among plots . CALIFORNIA AGRICULTURE , VOLUME 47 , NUMBER 6 20 above the vines . The containershad an adjustable funnel opening at the bottom ; by changing either the funnel opening or the tractor speed , the release rate could be controlled.A series of tests were con - and vi - ducted to determine the number ability of eggs delivered and the result - ing number of lacewinglarvae in the field . The number of lacewingeggs deliv - ered to each vine was measured by col - lecting 0.75 - oz ( 25 - ml ) samples of the egg / corn - gritmixture at the beginning and toward the end of one 2 - gallon ( 7.6 - liter ) release batch . The number of vines covered by each sample was recorded . The samples were dissectedin the labo - ratory , and the number of live , hatched , crushed ( fromthe mixing process ) and dead ( fromthe insectarymix ) eggs and live or dead larvae were recorded . After delivery to the vines , egg mor - tality ( before egg hatch ) can be affected by high temperatures , placement on or off the vine and predators ( seeCalifornia Fig . 1 . Average leafhopper densitiesfound in lacewing release and no release plots in September - October1993 ) . Agriculfure , three Thompson seedless vineyards in ( A ) 1991 anwe ) 1992 . C . carneaeggs were re - Presumably , these mortality factors have leasedat approximately3,50O / acre in the first brood and 7,0001acre in the second brood . a greater effectthe longer the egg is in Mean leafhopper densities , in each brood and vineyard , topped with different letters are the before egg hatch * To test the significantlydifferent ( P < 0.05 ) . mortality of fresh eggs and compare egg and larval releases , three - leaf plots were used , set in a randomized block design , with three treatments : 1 ) no release , 2 ) C . Comanche eggs per plot and three fresh 3 ) three C . Comanche first instar larvae per plot . Leafhopper and lacewing den - 2 or 3 days , sitieswere determined every until no lacewinglarvae were found . To determine lacewinglarvae recov - ery in the field , we sampled 3,000 to 6,000 leaves in each commercialvine - yard monitored in 1991 - 92,5to 10days after the lacewingrelease dates . The number of live or hatched eggs ( onre - stalks ) and lacewinglarvae were corded . Experimentalplot results Results in the experimentalplots for each year generallyshow lower leafhop - per densities in lacewingrelease plots 1 ) . In the than in the controlplots ( table 1990 cage trial , the difference between the release and controlplots was great - est at the release rate of 36,000 eggs per acre , which resulted in a significant42 and 29.4 % reduction in leafhopper num - bers in the second and third broods , re - ( P < 0.05 ) . However , at cur - spectively rent costs for lacewingeggs , about $ 3 per 1,000 , that release rate may be eco - nomicallyprohibitive ( about $ 198 per acre ) for the level of control achieved . Also , the cages prevented the lacewing larvae from moving off the vine and predators of the lacewingsfrom moving CALIFORNIA AGRICULTURE , NOVEMBER - DECEMBER 1993 21 correlated to the leafhopper density at 100 Fig . 2 . The average the time of release . At low leafhopper 0Control leafhopperdensity in densities , lacewingsconsume less , be - 0 C . Comancheeggs three - leaf plots that cause of the time spent searching for receivedfirst instar 0 C . Comanche larvae C . sparse prey , among other factors . T Comanche larvae was 5 80 significantly lower a Release method results Q ) - than in the control \ I / \ Results from the egg delivery test plots or in the plots showed that 4.0 , f 0.5 , ml of the corn grit C . that receivedfresh Ea Comancheeggs ( P c and egg mixture was delivered to each Q 60 0.05 ) . Field hatch of vine . The averagenumber of eggs in Q freshly laid eggs was 0 each 25 - ml samplewas 39.5 , f . 6.2 , mak - 20 % in this lessthan 6.3 ing egg delivery approximately E study . Mean leafhop - Q lacewingsper vine , or 3,160 per acre in per densities , on each each release . This number corresponded 3 40 sample date , topped well to the growers â?? desired release level Releasedate l I with different letters , of 3,0004,000 lacewingsper acre . How - are significantlydif - ever , delivery of eggs throughout thenum - ( Pc 0.05 ) . ferent vineyard was uneven . The average 20 ber of lacewing eggs per 25 - ml sample taken at the beginning of one release 0 10 15 5 Days batch ( 55.3 , f 8.6 ) was sigruficantly greater than the number collected at the end ( 23.9 , f 3.9 ) ( P = 0.003 ) . The results implied that as the tractor moved the eggs sifted to the bottom of the release Commercial vineyard results container and were delivered in greater onto the vine , which most certainly af - Results in 1991show a trend of lower numbers to the beginning rows . There fected the results . leafhoppernumbers in lacewing release was also a great range ( min . 5 , ma . 119 ) In 1991 , we changed the release rates plots than in no release plots ( fig.la ) . In in the number of eggs per sample , which to more closely reflect commercial rates , the first brood , there was a significant ( P indicated an uneven distribution of eggs typically around 3,000 to 4,000 lacewings < 0.05 ) reduction in leafhoppersin only in the field . per acre at each release , with one or two one vineyard ; however , in that vineyard Results from the studies testing the releases in the first and again in the sec - the 34.9 % decrease , from 23.2 to 15.1 viability of deliveredeggs showed that ond leafhopperbroods . At the higher re - leafhoppersper leaf , brought the aver - the method of egg dispersal caused lease rate of 8,000 lacewings per acre , a sug - age leafhopper density down to the some egg mortality , which can be ex - significant 33.6 % and 31.4 % reduction in gested economic injury threshold of 15 pected with almost any delivery system . leafhopper density were found in the leafhoppersper leaf ( GrapePest Man - After dissecting the mixture , we found first and secondbrood , respectively ( P < agement , DANR publicationNo . 3343 ) . 0.05 ) . Results were less consistent at the 62 % survivorship of the eggs delivered In the second brood , there was a sig - lower release rate of to the vines ( liveeggs plus larvae ) , 4,000 lacewings per nificant reduction in leafhoppersin each acre , tested on both release schedules.In 35.5 % crushed eggs ( from the mixing vineyard ( fig . la ) . But although signifi - process ) and the calendar - daterelease , a 31.2 % de - 2.5 % dead eggs . The low cant , the reduced leafhopper densitiesin crease and a number of dead eggs is typical for the 12.9 % increase in leafhop - vineyards 1and 2 remained above the material received from insectaries , with per density were recorded in the efirstc - suggested economic injury threshold . most mortality occurringafter shipment , and second leafhopperbroods , resp Thus , at leafhopper densities above 30 during storage and delivery.The per - tively . In the synchronizedrelease plots , per leaf , the release rates used - appeared centage of live eggs delivered to the there was a 16 % increase and a 12.9 % to be too low to bring about the neces vines was acceptablewhen compared decrease , respectively . sary ( more than 50 % ) decrease in leaf - with other deliverymethods . For ex - In 1992 , there was no sigruficantbe - hopper numbers . In vineyard 3 , leafhop - ample , air delivery of eggs to vines tween - treatmentdifferencesin the first per density was below the suggested places much of the material on the brood leafhopper densities.In the sec - economicinjury threshold in both the re - ground , where it will remain . The corn ond brood , comparingreleases of C . lease and control plots , and the average grit may cause some mortalityby in - carnea , C . comanche and C . rufilabris , only reduction in release plots amounted to C . rufizabrissigruficantlyreduced leaf - creasing egg desiccation.Other mixing only 2.4 leafhoppersper leaf . hopper density compared with the con - substances , such as vermiculite , have In 1992 , leafhopper densitieswereug - been reported to result in less egg mor - trol plots ( P < 0.05 ) . Leafhopper density , low ( fig . lb ) , never exceedingthe s tality , but were difficult to use with the at the time of the release , was fewer than gested economic injury threshold . In cooperatinggrowers â?? systems . Of 5 per leaf , far below * y suggested eco - only one of the three vineyards , vine - course , different release methods may be nomic injury level , which reduces theison yard 1 , was a significantreduction in more suited to other crops . importance of this trial as a compar leafhopper densitiesrecorded , a 36.7 % The egg and larvae release experi - of lacewing species.However , compar - reduction of leafhoppernumbers in theh ment , with C . Comanche in three - leaf ing data from the other trials over the hand release treatment comparedwit plots , tested field egg hatch of fresh in - three years , it was clear that with similar the control plots ( P < 0.05 ) . The actual sectary eggs . Results showed that egg release rates there was a lower - per - leaf decrease was 3 leafhoppersper leaf . As hatch took over 4 days , with less than leafhoppermortality when leafhopper in the experimentalplots , the effective - 20 % egg hatch . The effect of egg com - densities were low than when they ness of lacewing releases is apparently pared with larval release on leafhopper were high . 22 CALIFORNIA AGRICULTURE , VOLUME 47 , NUMBER 6 densities was evident . There was no dif - ferencebetween leafhopper numbers in egg release and controlplots . In plots re - ceiving larvae , leafhopper numbers were significantly ( P < 0.001 ) lower than those in the control ( fig . 2 ) . From this work and field observa - tions , we agree with the many insectary managers who suggest that it isbest to release lacewingswhen eggs are ready to hatch or already have begun . For vineyards , we suggest a 25 % to 50 % egg hatch at the release date . While there will be some cannibalism , the viability of the material delivered to the vines will be increased . Results of the larvae recovery test showed no sigruficantdifference ( P > 0.05 ) between release and controlplots ; 1larva per 1,000 both had fewer than leaves sampled . This poor recovery fig - ure does not necessarily mean that there were low lacewingdensities in the field ; it reflects the difficulty of sampling for lacewinglarvae , given their mobility and the low release rate compared to the number of leaves on the vine . Evidence of high natural lacewingpopulations was obvious from the number of eggs laid on stalks in both the release and controlplots . The highest densities of Staff Research Associate Glenn Yokota monitors for leafhopper nymphs and lacewing lacewingeggs recorded ( 15eggs per 100 eggs and larvae in a commercial vineyardtrial . leaves ) were in vineyards adjacentto peach or almond orchards , which had ery of the eggs . Improved methods are wings must be ordered in advance to en - not received any commerciallacewings . currently being developed by university sure timely delivery and then , after the However , the low number of larvae and insectarypersonnel . Until a method lacewingshave been shipped to the found in these vines again raises the has been perfected , to reduce egg mor - ed grower , the release has to be scheduled question of the importance of the natural tality , we suggest applying a rate bas around other management practices , Calgornia enemies of the lacewing ( see on a 25 % to 50 % egg hatch at the release such as irrigation . September - October1993 ) . Agriculture , date . Insectariesalso stress the impor - Our studies suggested how the level Conclusions tance of proper storage before delivery of leafhopper controlwith augmentative and will work with their customersto lacewingreleases could be improved . Green lacewingsare one of the most deliver viable material at the proper First , leafhopper densities should be common commerciallyreared natural time . carefully monitored so lacewingreleases predators . Our studies in experimental can be matched to the beginning of each plots and commercialvineyards showeds leafhopper brood . This will pair the that releases of green lacewingsat rate K . M . Daane is Associate Specialist , G . Y . newly hatched lacewingswith the between 3,000 and 8,000 per acre for Yokota is StaffResearch Associate , Y . D . smaller stage leafhoppers.Monitoring each leafhopper brood ( costing $ 9 to $ 24 Rasmussen was Laboratory Assistant , Y . the leafhopper density in each block will per acre for each brood ) reduced leaf - Zheng was Posfdoctoral Research Associate , also provide the grower with a better de - hopper densitiesup to 35 % . However , and K . S . Hagen is Professor Emeritus , termination of which blocks are appro - there was a great variabilityin release Laboratory of Biological Control . priate for lacewingreleases . Our results - effectiveness , with leafhopper densities Fundingfor this research was provided suggested that leafhopper densities be in some release plots showing no differ - by the California Table Grape Commission , tween 15and 25 per leaf can be reducedry ence compared to controls . the California Raisin Advisory Board and to below the suggested economicinju The method of releasing the lace - the UC Statewide IPM Project . threshold ( 15per leaf ) with lacewingre - wings was an important factor in their The authors thank Bill Barnett , Areawide leases . However , leafhopper densities effectiveness.Egg delivery to the vines IPM Specialist ; Jake Blehm , Buenaetrick , greater than 30 per leaf cannotbe re - was uneven throughout the vineyard , Biosystems Insectary ; Everett Di duced below the threshold at release and there was up to 38 % egg mortality Rincon - Vitova Insectaries ; Hunter Nadler ; rates economicallycomparableto insec - ( in delivered eggs ) . Proper release tim - Sinthya Penn , Benepcial Insectary ; and Rob ticidal treatments . Similarly , at low leaf - ing was also important , with rebeases Roy , Gallo Vineyards , for helpful sugges - hopper densities ( fewer than 5 per leaf ) synchronized to leafhopper egg hatch tions throughout the project ; and the the decreasein leafhopper numbers is resulting in a greater reduction of leaf - dar Hansen , KAC , Nadler , Rocca , Radoicich , not economicallyefficient . hoppers than releases based on calen Smeds , Swansen and Yokotafarmsfor use of Finally , the most important part of dates . Unfortunately , synchronizedre - their vineyards in some of the experiments . the release program is the careful deliv - leases are more difficultbecause lace - CALIFORNIA AGRICULTURE , NOVEMBER - DECEMBER 1993 23