8.0 ALTERNATIVES TO PESTICIDE USE AND APPLICATION 8,1 Introduction The amount of pe::: :- :--::.=:_:: qplied in California is large, and pesticide users would deem c,·11 --" ": :2 necess:':i·y,. A co!lsiderable portion of the. pesticides applied fi!,c!,; '-:3 ·:1ay into the ~tmosp;1ere and contributes to the air pollution problem. .e:2 is to be any reduction in air pollution ca~sed by pesticides. it must almost certainly involve shifting to alterna­ tive ways of pest control and, to some degree, through using better appli­ cation methods to ensure t~at a higher percentage of the pesticide applied reaches the target organism. These alternative methods are discussed here, 8.2 Alternatives to Pesticide Use 8.2.1 Biological Control Many natural enemies cf destructive pests are already being used for 1 pest control, primari1y in agriculture,- and methods are being developed 2 for using a variety of different organisms for various kinds of pests. The organisms imported for the destruction of pests thus far have been mostly arthropods (insects ar1 related groups), but other organisms have also been used to some deg0~2. For example, fungi have been used to control 3 4 weeds, fish to control masqLli~Js and bacteria and viruses to 6 7 con t ro l 1nsec. t s~ anaI various. c~oorganisms to control plant pathogens. The nature of b1ofoqica1 control. The ·term "biologica1 control" has been defined as ''the act~o~ cf p2rasit2s. pr2datcrs, er pathogens in main- taining another organisms J □ ~~1ation density at a lo~er average than would 14-1 . 8 occur in their absence." Biological control is part of the 11 natural control" through which biotic and abiotic factors operate to prevent a population of organisms from increasing to infinity when the number of offspring produced is greater than the parent stock. We are not usually aware of the effective operation of biological control, but it becomes apparent in some instances when the balance of the control is disrupted. This kind of disruption has been observed where pes­ ticide applications have decimated the predators of an insect pest and allowed the pest population to increase dramatically. 9 In a natural biological community, the populations of individual species tend to fluctuate above and below the average density for each species. Some species will remain rare in a given area while others will be abundant. Each population may be said to vary within certain limits about a typical mean density or equilibrium pas ition . 10 A similar dy­ namically changing population equilibrium is considered to exist among 10 various organisms in an agricultural crop area. , 11 The equilibrium position of a population can be shifted upward or downward by changes in the favorability of the environment. More favorable conditions consist of readily available food, optimal temperature and moisture, etc. Competition for food, predation, parasitism, etc. are un­ favorable and can lead to a lowered equilibrium position. 11 A small number of the pest organisms can be tolerated in essentially every crop and in most other places where pests occur. Often, the level considered tolerable in a crop is the number of pests which would cause damage equal to the cost of controlling or suppressing the pest population. 10 This level of pest infestation is called the 11 economic threshold." It 142 should be recognized that pests cannot be permanently eradicated by any method except in smal1 isc1ated areas. The goal of biological control is not to eliminate pest~ ·· ··•-::: · but to keep thei'' populations well below the economic threshold -~?~?~J~e, in areas where adequate biological control is operating, ·::·::: ~':::::::ice of a possible !Jest organism is not considered to be a proj1 2~ :sq~iring a ccn~~Jl action. Application ~f bic~saica1 control. Since bio1ogica1 pest control functions by the actions of other living organisms, man's activities in applying biological control have been limited to three areas: (1) impor­ tation of natural enemies of pests, (2) augmentation of the action of the hatural enemies through ~edification of the environment, ~nd (3) mass­ production and release of species capable of destroying members of pest 12 populations. The first of these approaches is preferred since, if it is ..,.. carried out successfu11y, the pest may be pemanent1y controlled by the natural enemy with no further action required. The other two approaches require continued action and ~ay be mo~e expensive in the long run. Each of these approaches avoid many of the disadvantages of chemical control methods. There is no chemical contamination of the environment, and de- . ' . , l , . ; " 1.2 ve l opmen t of hos t res 1 s-ca.nc2 1s 111 gn y 1..m 11 i(e iY o Damcge to nontarget organisms and disruptions t~e envircnme~tal balance are rare from in- sects, bacteria, a~d Importation of natL11··,d enem'les, The term "natural enemies 11 is used to refer to any insect or oth,2r O:"g2rrism i,.ilrlch 1s parasitic or predatory on another, particularly Although exotic natural enemies are often imported to cantro 1 specific pests ich are their natural hosts, they may be useful in the conttol of other, related pests as well. 14.3 A large part of the problem with pests has resulted from the accidental entry of the pest into an area without the parasites or predators which keep them under control in their native habitats. It has been estimated that 60 percent of the major arthropod pest species in the U. S. and more than 60 percent of the plant species recognized as weeds in California are 14 from other countries.· The best place to 1oo k for organisms capabl e of destroying these immigrant pests is the pests' native lands where their natural enemies exist. A considerable part of the biological control effort is spent in seeking out and testing such organisms. It should not be thought, however, that the only species which will attack a pest are those which originated in the same area. The introduced oriental fruit moth Grapholitho molesta (Busek), for example, is reported 15 to be attacked by as many as 56 species of parasites in the United States 16 and 25 in France and Italy. A successful program for importing a pest's natural enemies requires well trained personnel and an adequate organization to ensure that an appro­ priate search is made for the right organisms. Necessary safeguards must be taken to prevent the accidental introduction of other harmful organisms. Although natural enemies of pests are sought in foreign lands, usually where the pests originated if it is known, predatory insects do not always show great host specificity. Bartlett and Van den Bosch 13 recorded some instances in which pests were controlled by insects from other areas. In one case, the grubs of a beetle from Korea and Japan, Anomala orienta1is, attacked sugar cane in Hawaii but were contro1led by a wasp, Campsomeris marg1n~lla. modesto (Sm.), which is native to the Philippines. It has been recommended that multiple importations of various kinds of 144 natural enemies should be made in order to increase the chances of obtaining the best natural enern) c~ f ~2st/host in a particul2r habitat or range of habitats. 12 I • I ' Natural enemies I,• ~ '" _...., ,--, been found during foreign explorations must be collected and some-~':::. - ·2c:•..,2d to pto'dde sufficient numbers and shipped to a quarantine laborat:,·: , ·:::,2 destfoa:fon count,··y. The collector or the quarantine laborat:,r~.: r:~us.t study and select n..~tura1 enemies based on their host preference, other characteristics of behavior 1 and their life cycle. 13 Such biological control agents must be thoroughly examined for the presence of diseases ape! seconda:·y p.aras ites which m.ay attack alternate, desirable hosts among native species.. 17 Organisms which show some promise of controlling a pest must be cultured for further testing, mass produced, distributed. and released into areas where damage from the host occurs; Sometimes the imported organism can be colonized, without mass production or elaborate testing to determine its ability to survive, by simply releasing a few indiv-Jduals in the vicinity of the host. Ordinarily, repeated releases are ~ade at a number of sites selected for environmental diversity. It has been suggested that adverse climate has been responsible for more failures of colonization than any 18 other single factor. t't',flrC•'•1menti:.1 va at"icns may also iimit a natural enemy to only a part c·:= thE c::,·2a occupi2d by its hosL Once a natural enemy of c pest species is established in an area it generally provides some de,gr22 of permanent biological control of the host; this may be disrupted by the actions of man. The effectiveness of b~a1oqical control. The biological control of 145 pests through the importation of natural enemies has worked very well in some instances and less well in others. 12 In the first well known application of the method, the threatened destruction of the California citrus industry by the insect, cottony-cushion scale, Icerya purchasi (Mask.), \vas stopped by the vadalia beetle, Rodolia cardinalis, brought from Australia in 1888. The cottony-cushion scale has not been a problem since that time except when the vadalia beetle population has been reduced by insecticide application. 19 Van den Bosch and Messenger1 listed 95 species of insect pests and 21 weed pests which have been completely or substantially controlled in dif­ fererit parts of the world by imported insects. The 12 insect pests con­ trolled in California are listed in Table 8-1. Two species of weeds have been substantially or completely controlled in California by imported natural enemies.