nea that resulted in its ability to survive Selection of the common field rates of a pesticide. Geographical variability green lacewing for The first stage of the laboratory selec- tion program entailed collecting lace- wings from widely separated areas of resistance to carbaryl California. We then screened the lace- wings with six pesticides to see if there Elizabeth E. Grafton-Cardwell 0 Marjorie A. Hoy was any geographical variability in the colonies' response to pesticides. If all of Lacewings, ladybird beetles, predatory applied for navel orangeworm control the lacewing populations showed a simi- mites, wasp parasites, and other natural and kept spider mites under control so lar level of susceptibility to all pesticides, enemies of pests are important biological that fewer applications or lower rates of we would assume that selection was not control agents in many integrated pest acaricides were needed. occurring in the field and the genes neces- management (IPM) programs throughout The adult common green lacewing, sary to develop resistance were rare. If California. These natural enemies, how- Chrysoperla carnea Stephens, is a widely so, laboratory selection could be slow and ever, are usually more sensitive to pesti- dispersing nectar-feeding insect that de- would require screening enough numbers cides than are the pests they attack. As a posits eggs on both orchard and field to pick up such a rare gene. Variability in result, when a pesticide must be applied crops. As a larva, it is a voracious pred- response to insecticides would imply that for a key pest that has no biological ator of aphids, mites, small lepidopterous field selection for resistance had already agents controlling it, the natural enemies larvae, psylla, and eggs of many insects. begun. of other pests are killed and secondary The lacewing has been shown to be rela- We collected adult C. carnea from al- pest outbreaks occur. tively tolerant of some chlorinated hydro- falfa in San Joaquin, Fresno, Kern, and There are several hypotheses to ex- carbons, pyrethroids, and microbial insec- Imperial counties during 1981 and 1982 plain why natural enemies may be more ticides. It is susceptible, however, to most and maintained them as four separate sensitive to pesticides than pest insects of the commonly used organophosphorus colonies. Adults, larvae, and eggs were and mites. One is that they have different and carbamate insecticides. Enhance- screened with the organophosphates dia- feeding habits. The natural defense sys- ment of the lacewing's tolerance of these zinon (50 percent WP) and phosmet (Imi- tems of plants may stimulate production pesticides would improve its effective- dan, 50 percent WP), the carbamates car- of detoxifying enzymes in pests that also ness in many crops. We report here on the baryl (Sevin, 50 percent WP) and break down pesticides. Since natural en- first case of laboratory selection of C. car- methomyl (Lannate, WS liquid), and the emies generally do not feed on plants, pyrethroids permethrin (Ambush, Pounce, they do not have these enzymes in suffi- TABLE 1. Pesticide concentrationsat which 50 EC) and fenvalerate (Pydrin, EC). cient quantities to detoxify pesticides. percent (LCso) and 90 percent (LCgO) mortality Adults were tested in petri dishes Availability of food after pesticide appli- occurred in first-staae common areen lacewina sprayed with a range of concentrations of cations also gives pests an advantage larvae collect;d from fourcounties " formulated pesticide in water plus a wet- over natural enemies. When pesticides Pesticide (field rate)' ting agent. Each dish containing five are applied, most of the hosts and prey of and colony tested LCsnt LCan adult lacewings was closed with tissue pa- the natural enemies are destroyed, which Permethrin (0.2 Ib) /b active inclredient/ga/ per, and adults were provided with food can cause the few survivors to starve. The San Joaquin ' 0.64 a 1.88 and water. Twenty adults were tested at Fresno 2.48 c 20.33 pest survivors, however, simply feed on Kern 0.23 a 11.20 each concentration, and mortality was as- plants and rapidly rebuild their popula- Imperial 1.72 b 4.45 sessed after 72 hours. tions. Thus, the pest population recovers Fenvalerate (0.1 Ib) Adult lacewings were susceptible to much more rapidly after treatment with San Joaquin 1.50 a 5.39 field rates of the organophosphorus and Fresno 1.40 a 2.86 pesticides and develops pesticide resis- Kern 1.63 ab 8.1 6 carbamate insecticides. In contrast, they tance more rapidly. Imperial 2.22 b 17.39 were tolerant of both pyrethroids, easily One method of improving biological Carbaryl (1.5 Ib) surviving field rates. This is a natural tol- control in agricultural IPM systems that San Joaquin 0.0013 a 0.0053 erance, not a field-selected resistance, be- Fresno 0.0023 b 0.0068 use pesticides has been to select the natu- Kern 0.0030 b 0.0063 cause all colonies responded at a similar ral enemy in the laboratory for resistance Imperial 0.0032 b 0.0158 level and because other investigators to one or more commonly used pesticides. Methomyl (0.45Ib) have reported similar results. Two or Predatory mites in the family Phytoseii- San Joaquin 0.0009 ab 0.0023 more of the colonies differed significantly Fresno 0.0012 b 0.0045 dae are currently the only biological con- Kern 0.0004 a 0.0035 in their response to carbaryl, methomyl, trol agents that have been successfully se- Imperial 0.0043b 0.0042 and diazinon, indicating that field selec- lected for levels of resistance useful in the Diazinon (0.5 Ib) tion may be occurring. San Joaquin Coun- field. In California almonds, strains of the San Joaquin 0.0023a 0.0085 ty lacewings consistently responded with (= Fresno 0.0024 a 0.0048 predatory mite Metaseiulus Typhlo- Kern 0.0011 a 0.0045 the greatest susceptibility, which corre- dromus) occidentalis (Nesbitt) have devel- Imperial 0.0043 b 0.0101 lates with the lower use of pesticides in oped resistance to organosphosphorus Phosmet (1 .O Ib) that county. pesticides in the field and to carbamates San Joaquin 10.0 a 20.3 We tested lacewing eggs with the six Fresno 17.5 a 72.0 and pyrethroids in the laboratory. The se- Kern 36.6 b 395.8 pesticides using field rates proposed for lected strains have been mass-reared and Imperial 158.5 c 3206.3 alfalfa mixed in 10 gallons of water: per- released to control Pacific spider mite, * Field rate proposed for alfalfa, mixed in 10 gallons of methrin, 0.2 pound; fenvalerate, 0.1 Tetranychus pacificus McGregor, and water. pound; carbaryl, 1.5 pounds; methomyl, t LC values in the same column for each pesticide two-spotted spider mite, T. urticae Koch. folzwed by the same letter indicate that the responses 0.45 pound; diazinon, 0.5 pound; and phos- The predatory mites have survived sprays of the colonies are not significantly different (p=0.05). met, 1 pound. Female lacewings were al-

22 CALIFORNIA AGRICULTURE, SEPTEMBER-OCTOBER 1986 100 100

p susceptible

- 90 90 -

- 70- - c- 5--70 .g- 50. * - a g 50 5- 30- I30:- -

r Carbaryl-6 10 - 10 - d

0 01-- 1 I8 I 1 I 1 ,0008 .003 ,006 .03 .3 1.5 7.5 15 ,0008 ,003 .006 .03 1.5 15 Carbaryl (Ib Alp0 gal) Carbaryl (Ib A1/10 gal) Fig. 1. Imperial County green lacewing larvae showed more than 80 Fig. 2. Genetic analysis of purified susceptible strain crossed with the percent survival after four generations of selection. All of highly carbaryl-resistant strain (after six rounds of selection) and their susceptible San Joaquin larvae died at concentrations above ,003. offspring indicated no single dominant gene was involved. lowed to deposit eggs on paper toweling. use of pesticides in that county. It is most Selection for carbaryl resistance oc- Each sheet of eggs was cut in two; one likely that resistance has not reached curred very rapidly in this assay (fig. 1). half was sprayed with formulated pesti- field spray levels because lacewing adults All San Joaquin County larvae died at cide in water and the other half was fly to many different crops to deposit rates above 0.003 pound active ingredient sprayed with water alone. None of the their eggs and so may be exposed to many per 10 gallons. Of the unselected Imperial pesticides tested affected egg hatch. pesticides during their lifetime. Because County larvae, 97 to 99 percent died at We tested lacewing larvae individually different pesticides are likely to have dif- rates above 0.03 pound, but after only one (to avoid cannibalism) in small wells of ferent modes of action, selection for any selection (carbaryl-1), mortality de- plastic microtiter plates. Each plate was one is slow when an insect is exposed to creased to approximately 90 percent at treated with a concentration of pesticide several at the same time. these rates. Mortality decreased to 50 to mixed with distilled water plus a wetting Although field-selected green lace- 70 percent after the second round of selec- agent, then air-dried the tops of the wells wings did not have levels of resistance tion (carbaryl-2) and to less than 20 per- were ringed with stickem. Grain moth useful against field rates, the existence of cent after four rounds of selection. Up to eggs, Anagasta kuehniella Zeller, were more tolerant strains prompted us to at- 80 percent of the selected lacewing larvae provided as food for the larvae. Mortality tempt laboratory selection. survived on formulated material at the was assessed after 48 hours. We tested 30 field rate recommended for alfalfa (ap- to 200 first-stage (instar) larvae at each Carbaryl resistance proximately 1.5 pounds active ingredient concentration. The Imperial County lacewing larvae per 10 gallons), compared with only 3 per- Like the adults, larvae tolerated field showed the greatest overall tolerance of cent of the unselected strain. rates of the two pyrethroids, as shown by pesticides and so were chosen for labora- An analysis of the mode by which the the fact that the LC,, values (the concen- tory selection with carbaryl. We screened resistance was inherited indicated that no trations at which 50 percent mortality oc- larvae because they are the predatory single, completely dominant or recessive curs) were higher than the field rates (ta- stage of the lacewing and because they gene was involved (fig. 2). The F, off- ble 1). The larvae were also highly are most directly and continuously ex- spring (produced by crossing the suscept- tolerant of the organophosphate phosmet. posed to the pesticide residues on plants. ible and resistant parents), F, offspring Since no susceptible colonies were found, First-stage lacewing larvae were ex- (produced by crossing F, individuals), and these are most likely natural tolerances. posed to carbaryl at a rate that allowed, the backcross offspring (produced by The larvae were susceptible to field rates at most, 10 percent of the lacewings to crossing F, individuals with susceptible of carbaryl, methomyl, and diazinon. In survive. Larvae were placed in the wells individuals) all responded in an interme- all cases, even for the three pesticides of the treated plates (77°F) for 48 hours. diate manner compared with the purified that the lacewings tolerated, there were Survivors were placed individually in un- susceptible and resistant strains. Recipro- significant differences in the responses of treated 1-ounce plastic cups with lids and cal crosses responded similarly, indicat- the four lacewing colonies, confirming the reared to adulthood at room temperature ing no sex linkage of the resistance traits. adult data suggesting that field selection (75" to 81°F). Their offspring were then The lack of complete dominance suggests is occurring. San Joaquin County lace- used for the next selection. We tested 24 that, in the field, interbreeding with sus- wing larvae showed the greatest suscepti- to 48 larvae from the San Joaquin and the ceptible lacewings would result in off- bility (lowest LC,, values) and Imperial original Imperial colonies as controls. Six spring with lower levels of resistance County larvae generally showed the generations of selection were performed than the resistant parent. The lack of greatest tolerance of the pesticides tested. using 0.003 and 0.3 pound active ingredi- complete return to susceptibility in the F, The greater tolerance to pesticides ex- ent carbaryl per 10 gallons of water for offspring indicates that, if carbaryl hibited by the Imperial County lacewing the first two selections, and 7.5 pounds for sprays were applied, carbaryl resistance larvae correlates well with the greater the last four selections. could be maintained by field selection.

CALIFORNIA AGRICULTURE, SEPTEMBER-OCTOBER 1986 23 Agricultural Experiment Station BULK RATE UNIVERSITY OF CALIFORNIA POSTAGE & FEES PAID Berkeley, California 94720 USDA Lowell N. Lewis, Director PERMIT No. G269 Publication PENALTY FOR PRIVATE USE. $300

Conclusions Our studies showed that common green lacewing larvae collected from widely separated areas of California had different levels of tolerance to six pesti- cides. The most tolerant larvae, collected from Imperial County, were selected in the laboratory for resistance to carbaryl. Carbaryl-resistant larvae exhibited more than 80 percent survival after four gen- erations of selection, in contrast to 3 per- cent survival of the unselected strain. This rapid selection response demon- strates the feasibility of selection for pes- ticide resistance in predatory insects. The mode of inheritance of carbaryl resis- tance in the selected strain of lacewing is not due to a single completely dominant or recessive gene. Thus, the level of resis- tance is lowered when the resistant strain interbreeds with susceptible lacewings. Although field tests of the carbaryl-re- sistant strain have not been conducted, it is interesting to speculate where this strain might be used for biological con- trol. The purpose of selecting a resistant strain is to help it survive carbaryl sprays used to control pests that are not its prey. Because carbaryl resistance is not domi- nant, interbreeding with susceptible lace- wings must be avoided. This can be ac- complished by using the selected strain where susceptible natives do not exist, such as in greenhouses. Where susceptible lacewings cannot be eliminated, the se- lected strain could be used only in inunda- tive single-generation,short-term control. The economics and mechanics of rearing and releasing adequate numbers of resis- tant lacewings for either type of program must be studied before the strain could be commercially available. Elizabeth E. Grafton-Cardwell is Postdoctoral Re- searcher, Department of Entomology, University of California, Davis, and Marjorie A. Hoy is Professor, Department of Entomology and Parasitology, UC Berkeley. The authors thank Ciba-Geigy, Dupont, Shell, Stauffer, and Union Carbide Chemical com- panies for providing the pesticides used in screening and selection. Partial support for this project was provided by the California Department of Food and Agriculture, Environmental Monitoring and Pest Management and Biological Control Services Pro- gram; and by the Western Regional Research Pro- ject w-84,“Establish, improve, and evaluate biologi- The green lacewing, shown here feeding on the egg of a grain moth, is a valued predator of cal control in pest management systems. ” pests in many crops. Its effectiveness may be enhanced by improving its tolerance to pesticides.

24 CALIFORNIA AGRICULTURE, SEPTEMBER-OCTOBER 1986