Carson, William

Nakakihara, Henry : Henry Nakakihara is Staff Research Associate, Department of Entomology, University of California, Riverside, Calif.

Trumble, John T

Monitorina anhid infestations on broccoli John T . Trumble 0 Henry Nakakihara 0 William Carson A p h i ds cause substantial economic losses property at the University of California , suitable feeding sites . Transmission takes to Californiaâ??s broccoli industry in three Riverside . At least 60 plants in each crop , place when virus particles adhering to the which were selected using a stratified ran - ways : by inserting their hollow beaks into or contained in the salivary mouthparts plant tissues and removing sap , by transmit - dom design , were monitored for aphids and glands are injected during feeding . Thus , a ting viruses , and by contaminating the mar - parasites each week between thinning and single green peach aphid can infect many keted product . Since California produces 95 head formation . Counts from the youngest , plants . of the broccoli grown in the United percent highest , and oldest leaves were recorded Throughout most of California , the green States , costs of pesticides , application equip - so that separately from entire - plant counts peach aphid produces a sexual generation in ment , and the labor associated with aphid locational preferences could be determined . the fall , and females lay eggs that overwinter control cause considerable loss of income . on peach trees . In the spring , winged adults Green peach aphid Aphid feeding often results in stunting , leave the peach trees and migrate to a variety of weed and vegetable hosts , including broc - curling , or yellowing of broccoli ; severeinfes - The green peach aphid , Myzus persicae tations may kill plants . Leaves distorted by coli . Offspring from these adults reproduce ( Sulzer ) , was the most common speciesin this aphid feeding or virus infection provide areas parthenogenetically ( nonsexually ) , so that study ( fig . 1 ) . These aphids are pale green to populations may expand quickly . In warmer sheltered from pesticides , and survivors can yellow , and the winged form ( alate ) has an ir - areas like southern California , parthenogen - immediately reinfest the plants . regular black pattern on the upperside of the etic reproduction may occur throughout the Once broccoli heads begin to form , some abdomen . Some plant damage occurred year without need for a sexual generation . aphid species migrate to and thus contamin - when populations reached extremely high ate the marketable portions . Pesticidal sup - levels , but green peach aphids were primarily Cabbage aphid pression of established populations is nearly a problem because of their ability to transmit impossible when aphids are shielded by the viruses . Cabbage aphids , Brevicoryne brmsicae tight , umbrella - shaped flower buds . Unfor - Winged females transmit viruses during ( L . ) , were easily distinguished from green tunately , biological control agents , such as migrations , moving rapidly from one poten - of their gray color and peach aphids because hover flies ( Syrphidae ) and parasites , follow tial host to the next , probing each in search of white waxlike covering . These aphids were their hosts into the heads and cause addi - gregarious , occasionallygathering in colonies tional contamination . Although washing the of several thousand . Such large groups were crop after harvest may reduce losses from quite destructive , often stunting the plants = Green peach aphid contamination , parasitized aphids , or and seriously reducing yields . Cabbaae aDhid â?? mummies , â?쳌 are often firmly attached to the In the cool northern regions of California , plant , so that repeated rinsings are required cabbage aphids overwinter in the egg stageon to dislodge them . Since much of the fresh Brassica . crop debris or weeds in the genus market broccoligrown in California is packed However , warm winters in southern Califor - for shipment in the field and cannot be read - nia permit parthenogenetic reproduction all ily cleaned , pesticidesare used to maintain an year , and 15 to 20 generations may be pro - insect - free crop . duced annually . Cabbage aphids are more The objectives of the study reported here tolerant of cold weather than the other aphid were to determine which aphid species are species attacking broccoli ; infestations gen - economically important and to document erally occur in the winter in southern Cali - when and where each occurs on the plant . fornia and in the spring and fall in northern Based on this information , an efficient , reli - California . able sampling plan could be developed . We Although they did not reach population densities as high as those collected the experimental data in 1980 - 81 of green peach of greater from three successive 0.4 - hectare ( 1 - acre ) aphids , cabbage aphids were Fall Winter Spring Fall Winter economic importance as a contaminant of plantings of â?? De Cicco â?? broccoli at the Uni - Coastal region interior Valley broccoli . Approximately 20 percent of the versity of Californiaâ??s South Coast Field 1 . Occurrence of primary aphid species Fig . harvested broccoli was contaminated in the Station in Santa Ana , and two successive in valley and coastal on broccoli grown fall and winter plantings , and cabbage aphids plantings at the Agricultural Operations areas of California . CALI1 - ORNIAAGRICULTURE , NOVEMBER - DECEMBER1982 15 These preferences appeared to be in response to nitrogen availability in the plants . The youngest and highest leaves near the apical meristem were rapidly growing and served as nitrogen â?? sinks . â?쳌 As the oldest leaves began to senesce , the nitrogen - containing com - pounds released by cellular breakdown were transported out of the leaves for use else - where in the plant , and substantial amounts of amino acidsand nitrogen became available in a form suitable for aphids and other sap - Biological control agents , such feeding insects . The other aphid species were as syrphid larva shown attack - usually found on the intermediate leaves , may ing cabbage aphid colony , unless one of the high - nitrogen niches was cause additional contamination of broccoli heads . available . Earlier in the season , when plant height averaged less than 10 cm ( 4 inches ) physiological differences between the leaves were minor and within - plant distributions of aphid species were not as well defined . Based on this information , early - season monitoring should includeaphid counts from Green peach aphid , shown entire plants . Once plants reach about 10cm , above right in parasitized state , sampling for the cabbage aphid is most effi - is a problem mostly because it transmits virus diseases . cient when only the youngest and highest leaves are sampled . The green peach aphid Parasitized cabbage aphids are can be effectively monitored by checkingjust so firmly attached to the often the underside of the oldest leaf . Researchers plant that repeated rinsings are in both England and the United States have required to dislodge them . demonstrated an â?? edge effect â?쳌 for aphid infestations ; borders of fields tend to have larger populations . Therefore , presence - or - accounted for over 90 percent of the insects most common aphids encountered that did absence sampling should concentrate on observed . Because cabbage aphids tend to not accept broccoli as a host . Therefore , we move from the youngest leaves into the broc - these areas to minimize sampling time and did not investigate the occurrence , distribu - maximize efficiency . This type coli heads , they must be controlled before of sampling is tion , and potential for virus transmission by heading to ensure a marketable crop . particularly important before heads begin to these visitors . form , since aphids must be controlled at this Other aphid species Distribution and sampling time if a marketable crop is to be produced . The turnip aphid , Hyadaphis erysimi Previous research at U.C . , Riverside , has Approximately two weeks after broccoli shown that , in the absence of viruses , broc - ( Kaltenbach ) , and the potato aphid , Macro - thinning , the aphid speciesbegan to segregate siphum euphorbiae ( Thomas ) , were occa - coli plants can tolerate at least 100aphids per by location on the plants . Cabbage aphids sionally found at low population levels but plant without significantyield loss . However , preferred the youngest and highest leaves ; were not considered to be of major impor - if viruses are prevalent , economic losses can green peach aphids were most common on tance . Turnip aphids are generally yellow or occur at much lower population levels , and the undersides of the oldest leaves ( fig . 2 ) . green , with black heads . Although similar in pesticideapplication may be required sooner . appearance to cabbage aphids , they could be Since aphid populations were often distrib - readily distinguishedby the absence of a wax - uted in clumps in the field , counts from just a like coating . The red biotype of the potato few plants were not effective for determining Youngest leaves o , 50 . aphid was the dominant form during fall and the extent of an infestation . Samples collec - - Highest leaves g5 early winter plantings , which greatly facili - ted throughout the field provided the best 111111 Oldest leaves c 5 0.40 . tated identification and separation of species . statistical picture of aphid density , but sam - 2 - - 0 Throughout the remainder of the study the pling from field borders ( especially those 2 u0.30 . green biotype predominated . The relatively downwind of fences or windbreaks ) pro - long cornicles ( tubular structures projecting duced more conservative estimates and pro - upward or backward from the rear of the ab - vided the earliest notice of aphid migrations . domen ) and legs , as well as the extended an - tennal tubercles ( protrusions on the head to John 7 : Trumble is Assistant Professor of Ento - which the antennae are attached ) , aided in mology , Henry Nakakihara is Staff Research distinguishingthis species . Associate , and William Carson is Laboratory Assistant , Department of Entomology , University Winged forms of Macrosiphum ambrosiae of Calsfornia , Riverside , Calif . All photos by Max ( Thomas ) , Aphis spiraecola Patch , and Fig . 2 . Niche separation by green peach and Badgley , Department of Entomology , U.C . , River - Schizaphis graminum ( Rondani ) were the cabbage aphids based on plant development . side . 16 CALIFORNIAAGRICULTURE , NOVEMBER - DECEMBER 1982