Mass Trapping with Blacklight: Effects on Isolated Populations of Insectsl

w. W. CANTELO; J. L. GOODENOUGH," A. H. BAUMHOVER,' J. S. SMITH, JR.,' J. M. STANLEY,· AND T. J. HENNEBERRY' USDA

ABSTRACT Blacklight traps were operated for 43 months at a density of 3 per square mile on an isolated tropical island, St. Croix, U. S. Virgin Islands, to determine the effect on populations of 25 insect species. Subsequently, the density of traps was reduced to 0.3 per square mile for] 8 months, and changes in the collections were noted. The test species were: Agrius cingulatus (F.), Callionima ramsdeni (Clark), Eumor- pha vitis (L.), Hyles lineata (F.), Manduca rustica harterti (Rothschild), Manduca sexta (L.), Xylophanes pluto (F.), X. tersa (L.), Heliothis virescens (F.), H. zea (Bod-

die), Ecpantheria icasia (Cramer), Gryllus assimilis (F.), Microcentrum triangulatum Downloaded from https://academic.oup.com/ee/article/3/3/389/2395318 by guest on 29 September 2021 Brunner, N eoconocephalus triops (L.), Schistocerca pallens (Thunberg), A crosternum marginatum (Palisot De Beauvois), Loxa pilipes Horvath, Nezara viridula (L.), ladera rufofusca Barber, Bothynus cuniculus (F.), Phyllophaga microphylla Moser, P. portoricensis (Smyth), Calosoma alternans alternans (F.), Conoderus sp. and Lacon subcostatus (Candeze). Many species had decreased populations as measured by BL trap collections during the 43 months, and within a year after the trap density was reduced most had surges to population levels as high or higher than those recorded during masstrapping. Lepidop- teran population indices were more affected than indices of other orders. Generally, most decreases and increases in populations appeared to be related to the trapping, but the numbers of some species that were removed by the traps were so low that any effect was indirect. Blacklight traps have a potential as a supplement for other control meas- ures or possibly as a control themselves if the trap area is sufficiently large or sufficiently isolated.

When blacklight (BL) traps were operated for Xylophanes pluto (F.), X. tersa (L.), Heliothis vi- 31;2 yr on an isolated tropical island, the populations rescens (F.) H. zea (Boddie), and Ecpantheria icasia of many species seemed to have been reduced (Can- (Cramer). Orthoptera: Gryllus assimilis (F.), Mi- telo et al. ]972a and b, ]973a), but the primary evi- crocentrum triangulatum Brunner, Neoconocephalus dence was drawn from the progressive decreases in triops (L.), and Schistocerca pallens (Thunberg), the collections in the BL traps. These decreases Hemiptera: Acrosternum marginatum (Palisot De could not be corroborated by data concerning infes- Beauvois), Loxa pilipes Horvath, Nezara viridula tation because of the difficulty in regularly finding (L.), and ladera rufofusca Barber, Coleoptera: infested host material. Nearly all the species studied Bothynus cuniculus (F.), Phyllophaga microphylla required noncultivated hosts for survival and develop- Moser, P. portoricensis (Smyth), Calosoma alternans ment. Therefore, the decrease in collections could alternans (F.), Conoderus sp. and Lacon subcostatus have been caused by other factors such as changes (Candeze). in the weather or land use. We sought additional in- Seasonal variations in collections and in the host formation about any trapping effect by reducing the plants of each species were reported in earlier papers density of the traps to 0.3/ mile" and observing the (Cantelo et al. ] 972a, band ]973a). collections for ] 8 months. The present paper re- Methods ports the results of these studies. The population trends of the following insects Ca. 250 BL traps were installed and operated from are discussed in the order given. Lepidoptera: Agrius May ]966 through December ]969 on St. Croix, an cingulatus (F.), Callionima ramsdeni (Clark), Eu- island in the Caribbean Sea of 84 mile". The catch morpha vitis (L.), Hyles lineata (F.), Manduca of insects was collected from 51-53 of these traps rustica harterti (Rothschild), Manduca sexta (L.), 2-3 times a week to obtain an index of the populations. At the end of December 1969, all but 25 BL 1 Received for publication 15 Oct. 1973. " Vegetable Laboratory, Agric. Res. Serv., Beltsville, MD 20705. traps were turned off. These 25 traps were then Formerly: Tobacco Insect Investigations, Agric. Res. Serv., St. Croix, V. I. operated from January 1970 through June 1971, and 3 Univ. of Tenn., Dept. of Agric. Engin.. Knoxville 37916. collections were made 3 times a week. The traps, Formerly: Electromagnetic Radiation Investigations, Agric. Res. Serv., St. Croix, V. I. and the locations, and physical and environmental 'Tobacco Res. Lab., Agric. Res. Serv., Oxford, NC 27565. information about St. Croix were described by Stan- • Southeastern Fruit and Tree Nut Res. Stn., Byron, GA 31008. Formerly: Electromagnetic Radiation Investigations, Agric. Res. ley et aJ. (197]). Serv., St. Croix, V. I. n [nseet Attractants Behavior and Basic BioI. Res. Lab., Agric. A possible criterion in determining whether mass Res. Serv., Gainesville. FL 32601. trapping affects insect populations is the change in 'Area Director, Western Region, Agric. Res. Serv., Phoenix, AZ llSooO. Formerly: Vegetable, Ornamental and Specialty Crops the collections during and after mass trapping. If the Insects Res. Branch, Entomology Res. Div., Agric. Res. Serv., Beltsville, Md. trapping suppresses populations, the collections will 389 390 ENVIRONMENTAL ENTOMOLOGY Vol. 3, no. 3 decrease during the mass trapping and increase after- (J anuary 1970) were compared with the collections wards. One could argue that reducing the trap den- expected if the collections were or were not affected sity (from 3/ mile' to 0.3/ mile") will result in higher by the other 230 traps operating. (In December mean collections in the remaining traps due to less 1969, ca. 255 traps were in operation at all times.) intertrap competition; then an increase in the col- The expected January collection, which assumed lections after the cessation of mass trapping would that the collections in each trap were independent of not represent actual changes in population. How- the collections in the other traps, was derived for ever, the distance between traps did not affect the each species by first calculating the average change trap collections of the tobacco horn worm (McFadden in collections between December and January for the and Lam 1968), the cabbage looper, or the com ear- 5 yr of trapping (omitting the December 1969- worm, (Sparks et al. 1967). January 1970 data). This rate of change was then Whenever trap density has affected collections, the multiplied by the observed December 1969 collec- traps have been much closer than in the present tion to obtain the expected January 1970 collection. Downloaded from https://academic.oup.com/ee/article/3/3/389/2395318 by guest on 29 September 2021 study. For example, Embody (1971) estimated that Also, we accounted for the assumption that each collections of pink bollworm moths would not be trap affected the collections of other traps by multi- reduced with traps located over 729 ft apart. Hart- plying the expected collection for independent col- stack et al. (1971) calculated that only a slight re- lection (unaffected by other traps) by 10.2, the ap- duction would occur in the collections of the com proximate multiple of the number of traps operating earworm and the cabbage looper if the traps were in December vs. the number operating in January. closer than 600 ft. Also, when the number of BL (We thus assumed a linear proportional relationship traps on St. Croix was increased in May 1966 from between the number of traps and the collections.) 9-250, the 12-month mean collection of tobacco When the observed and expected January collec- homworm moths increased the next 4 months, rather tions were compared (Table 1), the observed collec- than decreased (Cantelo et al. 1972 a, Fig. 3). tion was within one standard deviation of 16 species Although the traps may have been too far apart for the calculated independent collection and 6 spe- during and after mass trapping to be in direct com- cies for the calculated dependent collection. For petition with one another, the great mobility of some only one species, E. vitis, was the observed collection of the test species could have influenced the collec- within a standard deviation of the dependent collections. To determine whether lower trap density re- tion but not the independent collection. In most sulted in higher mean collections, the collections in cases the observed collections were much closer to the first 4 weeks after mass trapping was stopped the independent than the dependent expected collec-

Table I.-Observed collections (per trap night) in January vs. expected collections if collections were unaffected (independent) or affected (dependent) by collections in other traps.

Observed collection Expected January collection (± I s.d.)' --- .. -- '--~ .--.------Species December January Independent Dependent

A. cingulatlls 0.26 0.18 0.23±0.15* 2.34± 1.55 C. ramsdeni .29 .74 .38± .17 3.86± 1.77 E. vilis .01 .02 .OO± .00 .02± .01* H. !ineata .03 .02 .01± .00 .I0± .03 M. r. harterti 1.24 .62 .51± .04 5.21± .41 M. sexta .40 .15 .21± .07* 2.18± .71 X. pluto .56 .86 .52± .28 5.32± 2.86 X. tersa .10 .18 .13± .05* l.31± .48 H. virescens .00 .00 .00 .00 H. zea .00 .01 .00 .00 E. icasia 1.58 3.16 2.69±1.87* 27.46±19.08 G. assimilis .20 .78 .94±1.19* 9.57±12.J2* M. trianglllatulII ') N.triops 6.06 3.96 5.91±4.17* 60.29±42.56 S. pallens J A. marginatllm .81 1.27 .64± .15 6.52± 1.55 L. pilipes .28 1.98 2.02±2.41 * 20.65±24.58* N. viridula .29 .72 .30± .13 3.06± 1.28 J. rufofusca .28 2.17 1.23± 1.61* 12.51±16.47* B. cuniculus 5.99 5.80 4.67±1.21 * 47.67± 12.38 P. microphylla .03 .03 .03± .03* .27± .33* P. portoricensis .02 .01 .OJ± .00* .14± .05 C. a. alternans .14 .02 .06± .05* .58± .54 Conoderus sp. .03 .03 .03± .03* .27± .33* L. subcostatus

• Text describes how estimates were calculated. • Indicates that actual collection was within I standard deviation of estimated collection. June 1974 C.~NTELO ET AL.: INSECT TRAPPING WITH BLACKLIGHT 391

reductions were calculated by using the formula Nt = Noe'l" "-v' where No = initial population; p = z rate of change in population size per month; t = 2 time in months after traps energized; Nt = population remaining after t months. Then several rates of recovery were calculated and plotted for the post mass .. trapping period (January ]970-June 1971) by using ;: the formula Nt = Noe'l"""" (Fig. 1A). The June ::: 3 o ] 966-April 1967 data are not included in the figure. w :z: The rates of reduction that approximated those ob- .. served for a species could be considered an estimate o of the efficiency of the trap system in changing the Downloaded from https://academic.oup.com/ee/article/3/3/389/2395318 by guest on 29 September 2021 1.0' size of the population of the species under the exist- ing environmental conditions. Thus, the greater the .8 rate of decrease, the more effective the traps. Also, the rates of recovery would indicate the ability of the species to increase when the pressure of BL trapping is removed. (Because ] 2-month means are used, there is a lag in the decreases and increases.)

Results 0 The populations of many species were affected by ;; 16 the pattern of rainfall during the test. Normally St. % C !12 Croix has 2 periods of drought a year, a total of ca. 5 months, but there was no drought from July 1968 through December 1969 (Fig. 1C). As a result, succulent vegetation (and presumably host material for the test insects) abounded, and the populations of many species increased during 1969. This re- sponse of tropical insect species to the rainfall pattern is usual, and larger collections normally occur FIG. IA.- Theoretical population indices showing sev· eral constant reductions in monthly populations from during or immediately after rainy seasons (Owen May 1966 to December 1969 and increases from Janu· ]969), (Janzen ]973). ary 1970 to J line 197 \. The initial and normal index Agriu.\· cingulatus was assllmed to be 10 insects/trap-night. B. Twelve- month moving mean collections of H. linea/a, N. viri- The population of the sweetpotato hornworm duJu, and C. ramsdeni. C. Monthly rainfall on St. Croix: showed no definite trend during the period of mass mean of all stations reporting ( ]6-22). trapping (Fig. 2A). However, a major increase occurred after the mass trapping stopped, an average tions. These data strongly suggested that the reduc- of ca. 14%/month from December 1969 to Janu- tion in trap density did not substantially affect the ary 1971. mean trap collections. The population of all species fluctuated consider- Ca/lionima ramsdeni ably during each year, partly because of the lunar The population of C. ramsdeni declined steadily cycle, brood maturation, and mortality, but primarily from September 1967 to February 1969 (Fig. 18) because of seasonal weather changes. We therefore and then surged immediately after the mass trapping clarified long-term population changes by minimizing stopped. Thus reducing the trap density apparently the seasonal and shorter cycling effects by calculating increased the mean collections though the calcula- a moving mean for every 12-month period during tions (Table 1) predicted the increase would be only the test, i.e., for the 12 months ending June 1967 about a factor of 2. The rate of increase from De- (the first 12 months of trapping), July 1967, August cember 1969 to December 1970 was ca. 16%/month. 1967 ... June ]971. Earlier data were available for Eumorpha vilis M. sex/a and were used to calculate the mean col- Populations of this sphingid were sharply reduced lections of this species; however, only collections of during the time of mass trapping; the rate of decrease females were used in the studies of M. sexta because was ca. 7 % / month. However, within 16 months from July 1968 to December 1969, ca. 240 of the after the mass trapping stopped, the population had traps were baited with virgin female M. sexla, which increased (at a rate of ca. 12 % / month) to the level increased the collections of males during this period. of the initial year (Fig. 28). As an aid in interpreting data arranged as moving means, models were prepared based on the assump- Hyles Iineata tion that a normal collection is 10 insects/trap per The population of this sphingid decreased steadily night and that several rates of reduction per month at a rate of ca. 5 % / month during the mass trapping. occurred from June 1966 to December 1969. The Within 7 months after the pressure of trapping was 392 ENVIRONMENTAL ENTOMOLOGY Vol. 3, no. 3

COLLECTION 1.6 population size being dependent to a considerable ex-

A tent on the population developing from insects that 1.4 had been in diapause for many months. We found

ORnLUS 1.2 0\55111\1 LIS (unpublished data) that on St. Croix the tobacco horn worm commonly diapauses for as much as a 1.0 year. If the number entering 'diapause was reduced

0.8 by the trapping (as appears quite possible) and if the insects emerging from diapause did constitute a 0.6 sizable percentage of the active population, the population of tobacco hornworms would not regain its 0.4 pretrapping level until all the diapausing insects from the broods exposed to the mass trapping had emerged and produced another brood. Downloaded from https://academic.oup.com/ee/article/3/3/389/2395318 by guest on 29 September 2021 Xylophanes pluto ---250 U •••" IN O'II"IION----:15 TlAPSIN O'&I",ION- 1.4 The collections of this sphingid declined from the initiation of the trapping until May 1969 and then 1.2 B 'C,"NTH_lllA increased steadily thereafter (Fig. 28). The trapping ICAIIA 1.0 apparently reduced the population, but the continual supply of food made available as a result of the lack 0.8 of dry seasons, in 1968-69 permitted a rate of de- velopment that exceeded the number being removed from the population by the traps. X. tersa The variation in the population of this moth can not be attributed to the trapping though the rapid J A J 0 J ••• J 0 increase in mid-! 970 resembled the trend of a re- -1967---196.----1969----1970- __ 1971_ covering population (Fig. 4B). He/iothis virescens FIG.2.- Twelve-month moving mean collection. A. A. cinKlllatus, G. assimilis, L. pilipes; B. E. icasia, E. Collections of the tobacco budworm were very low vitis, X. pluto. throughout this study. Therefore, we did not expect reduced, the population had regained its initial level COLLECTION (Fig. I B). This is substantial evidence that the trap- 14 ping suppressed the population. 12 Manduca rustica harterti A

The rapid drop in the collection of this sphingid at IOTHYNUS CUNICULUS the beginning of the mass trapping, the continued J,..---./ decline thereafter, and the surge in collections that occurred when the mass trapping stopped suggest that trapping suppressed the population. From De- cember 1969 to January 197 I, the rate of recovery was 17% Imonth (Fig. 3A). During the last 18 months of mass trapping the 5 I survey traps collected 37,394 moths of this species, an average of 1.31

trap-night. On the other hand, during the 18 months ---2S0 nA'S IN 0' ••.••'ION----25 'I"'S IN O'II •.'ION'" 3.5 (January I97G-June 1971) after the mass trapping stopped, the 25 survey traps collected I 17,105 of 3.0 B this species, an average of 8.5ltrap-night. 2.5 Manduca sexta The collections of tobacco hornworms declined 2.0 steadily from September 1966 to April 1970 when they were 89% below the initial collectons. There- after, the collections increased slowly (at the rate of 5%/month) until by June 1971, they were ca. % of the collections of the initial year (Fig. 4B) . This marked effect of mass trapping confirmed the results JOJAJQJAJOJAJOJA of the Oxford, N.C., workers (Lawson et a!. 1963, _1967 1961----1969 -----1910- 1971_ Gentry et al. 1967, Lam et al. 1968, 1971). How- ever, the slow recovery after the cessation of mass FIG. 3.-Twelve-month moving mean collection. A. B. cuniculus, M. r. harterti, J. rufofusca; B. A. marRi- trapping was unexpected. Possibly it was due to the na/um, grasshoppers, P. portoricensis. June 1974 CANTELO ET AL.: INSECT TRAPPING WITH BLACKLIGHT 393

COLLECTION 0.20 in April-June 1969 was 78-30 I. Snow et al. (1969) estimated that in 1967 the BL trap system caught

_HILIOTHIS ca. 5% of the total population, but we calculated VIIESCINS X 10 from the data Snow et al. (1971) reported for 1969 the BL traps caught 0.03%-0.1 % of the total. How- LACON SUICOUATUS AND ever, we assumed that the irradiated males were as CONOD.aUS'P. attracted to the virgin females as were the native males. This is not true for M. sexta (Cantelo et aI. 1973b) and may not be so for H. zea. In that case, the trap efficiency would be increased proportion- 0.04 ately. In view of the trap efficiency and the estimated earworm production vs. captures, the numbers removed would not be expected to have a measurable Downloaded from https://academic.oup.com/ee/article/3/3/389/2395318 by guest on 29 September 2021

------250 n",s IN O'IiAflON----25 n",s IN OPUATION- effect on the population. Ecpantheria ;casia The trapping appeared to have no effect on the population of this species; although the surge during 1970 suggests that lowering the trap density removed a suppressive factor (Fig. 28). Gryl/us assimilis The trapping did not appear to have an effect on the population of the cricket, and the plateaus shown in Fig. 2A indicate that the population remained the same size for considerable periods. The ]969 surge was presumed to be an indirect result of the unusual rainfall that year. ~-- ' •• 7---._ --- --196'~ -~~196.~---'970 '911_ Microcentrum triangulatum, Neoconocephalus triops, FIG. 4.- Twelve-month moving mean collection. A. and Schistocerca pallens P. microphylla, H. zea, H. I'irescells, L. subcostatlls, and COllodems sp.; B. M. sexta, C. a/temans a/temans, X. The 3 species of grasshoppers were recorded to- ler.m. gether. As Fig. 38 shows, the trend in population was similar to that of G. assimilis during the period of mass trapping. The limiting agent apparently was that the trapping was influencing the size of the the amount of food available, which was in turn population though there was a continued decline in limited by rainfall. the collections during the mass trapping (a 97% reduction from the first year to December 1969) Acrosternum marginatum and a steady increase (rate of 30%/month) after The population trend of this stinkbug was similar the mass trapping ceased (Fig. 4A). These changes to that of several of the test species, that is the col- are difficult to ascribe to anything but the trapping, lections declining moderately until ]969 and then The rate of increase may have been reduced because increased in 1971 to a level ca. double that of the 28 sticky traps baited with virgin female moths were initial year (Fig. 38). operated from October 1970 to September 1971 and Loxa pili pes because similarly baited electric grid traps were The population trend of this stinkbug was similar operated in May and June 1971 (Goodenough and Snow 1973), to that of A. marginatum (Fig. 2A). This test species and C. ramsdeni were the only ones to show a H. zea surge as soon as the number of traps was reduced, a The com earworm, in a similar fashion to H. result that would be expected with intertrap compe- virescens, experienced a 94% reduction in collec- tition. tions (Fig. 4A) during mass trapping though these Nezara viridula collections too were very low except during Novem- The trend of the population of the southern green ber and December 1970 when the high relative col- stinkbug was like that of A. marginatum during the lections increased the total 12-month mean collec- mass trapping, but for unknown reasons, the populations substantially above those prevailing at the be- tion declined sharply during] 971 (Fig. 18). ginning of the test. The collections were affected by other traps that were baited with virgin female moths ladera rutotusca and the populations by the release of sterile males The population of this rhopalid bug appeared to that occurred in another study (Snow et al. 1968, be strongly affected by the trapping (Fig. 3A). It ]969, ]971). From the recapture data of Snow et dropped at the rate of ca. 24%/month to ca. 5% al. (1969, ]971), we estimated that the daily native the size of the initial year and remained there until population in July-August 1967 was 242-515 and the end of ]968. In ]969, it rose to a higher plateau 394 ENVIRONMENTAL ENTOMOLOGY Vol. 3, no. 3 where it remained until the mass trapping ceased. populations of several insect species were substan- Then it increased at the rate of ca. 10%/month. tially reduced by the BL trapping. As might be ex- Bothynus cuniculus pected, species that are nocturnally active and have several generations a year, e.g., the lepidopteran test The collections indicated that the population of species, were suppressed to a greater degree than this may beetle declined moderately until October species that are primarily diurnal and have fewer 1965 and then began increasing until it had reached generations per year, e.g., the orthopterans. The the level of the initial year by the end of 1970 (Fig. strong flying species appeared to be more affected 3A). The slowness of the changes in population than the weaker fliers by the trapping presumably be- may be attributed to the 3-month or more life cycle cause the individuals would have a higher probability of this insect (Fennah 1947). of being trapped. Apparently the populations of Phyllophaga portoricensis many lepidopteran species that were not recorded Downloaded from https://academic.oup.com/ee/article/3/3/389/2395318 by guest on 29 September 2021 The population trend of this may beetle was very were suppressed. In 1970, the year after the mass similar to that of B. cuniculus except that a great trapping stopped, St. Croix experienced an outbreak surge occurred after mass trapping stopped (Fig. of many lepidopteran species (e.g., Melipotis spp. 3B). The collections increased at an average rate of and Spodop/era spp.) for the first time since 1966, 10%/month. the first year of the mass trapping. These outbreaks had previously been a yearly phenomenon. P. microphylla The results we report have been based entirely on This may beetle had changes in population similar the numbers of insects caught and not on any pos- to those of B. cuniculus (Fig. 4A). sible indirect effects of trapping. However, some Calosoma alternans alternans species; particularly H. virescens and H. zea, de- The irregular fluctuations in the population of this clined dramatically during the trapping period, even carabid beetle probably reflect the quantity of the though only small numbers were caught, and then host material that was available for the previous recovered rapidly after mass trapping ceased. Our generation. The mass trapping did not appear to observations indicate that in attracting insects re- have any influence (Fig. 4B). peatedly to a given location, various predators be- came habituated to these sites. (This was also true Conoderus sp. and Lacon subcostatus at insect release sites). Thus it seems likely that The 2 species of click beetles were recorded to- the indirect effects of trapping, i.e., causing insects gether. The populations appeared to be suppressed to congregate near the trap sites, where they are by the mass trapping since an 8 % reduction per vulnerable to predators, may play an important role month occurred from the initial year to December in suppressing these species. Another possibility is 1968. After the trapping ceased, the population in- that the frequent exposure to BL had a detrimental creased steadily for the remainder of the study effect on behavior or shortened their lives as sug- period (Fig. 4A). The slow recovery may reflect gested by Levengood (1969). Certainly, during the their long life cycle. early part of the trapping period, large quantities of insects were caught, and some traps were completely Discussion filled in one or 2 nights (ca. 40 liters of insects). The collections of most of the study species de- During the latter part of the trapping period, only creased during mass trapping and increased when the small quantities were caught (frequently no more mass trapping was stopped. Moreover, decreases than I liter in 51 traps). In addition, the weights of (1966-1969) occurred despite steady increases in the trap collections taken over the 17-month period the annual rainfall during this period. At the Federal beginning with the last month of mass trapping pro- Experiment Station, the annual rainfall was 27 in. vided evidence of a general buildup of insects. They in 1966,32 in. in 1967,36 in. in 1968, and 62 in. in were (in grams/trap per night minus the weights of 1969. The average rainfall at this location is 37 in. the orthopterans): 1969, December-I 4; 1970, Janu- Several species (A. cingula/us, X. tersa, C. rams- ary-IS, February-21, March-14, April-13, May deni, E. icasia, A. marginatum, L. pilipes. P. portori- -110, June-196, July-132, August-49, Septem- censis, and P. microphylla) did not have major ber-43, October-74, November-70, December changes in collections during the mass trapping, but -42; 1971, January-30, February-17, March- the collections after mass trapping ceased increased IS, April-57. to several times the highest previous level. This Probably as the food reservoir for insectivorous could indicate that (1) the population was low at predators and parasites diminishes (that is, as insect the beginning of the mass trapping, and the trapping populations are reduced), the increased competition kept it low despite favorable environmental condi- for food increases the pressure on remaining host tions, but it increased greatly when the trapping pres- populations. If the reduction in total insects avail- sure was reduced; or (2) the surge was the result of able for food limits reproduction of predators and environmental factors only; or (3) a trap density parasites, the competition will stabilize at a lower dependent factor was present that is not apparent level, which will decrease the pressure on the insect from Table 1. hosts. Therefore, resurgence of many populations We believe the evidence is convincing that the after the end of mass trapping to levels far exceeding June 1974 CANTELO ET AL.: INSECT TRAPPING WITH BLACKLIGHT 395 the initial levels may indicate that the rates of in- Goodenough, J. L., and J. W. Snow. 1973. Increased crease were approaching the net biotic potential be- collection of tobacco budworm by electric grid traps cause the predators and parasites could provide so as compared with black light and sticky traps. Ibid., little restraint. These and other possible factors asso- 66: 450-3. Hartstack, A. W., Jr., J. P. Hollingsworth, R. L. Ridgway, ciated with trapping require further study. and H. H. Hunt. 1971. Determination of trap In an isolated habitat, a system of BL traps has spacings required to control an insect population. potential as an adjuvant to control some species. Ibid., 64: 1090-1100. With sustained trapping, it is possible that no other Janzen, D. H. 1973. Sweep samples of tropical foliage controls would be necessary in some years. insects: effects of seasons, vegetation types, eleva- tion, time of day and insularity. Ecology 54: 687- Acknowledgment 708. Lam, J. J., Jr., A. H. Baumhover, and C. M. Knott.

We gratefully acknowledge the assistance of M. 1971. Hornworm population suppression in a large Downloaded from https://academic.oup.com/ee/article/3/3/389/2395318 by guest on 29 September 2021 Garcia, M. B. Peace, O. Skov, J. Fuertes and C. area with traps using black light lamps. Trans. Am. Asencio, research technicians on St. Croix, in this Soc. Agric. Eng. 14: 706-8. research. The comments on the manuscript by E. F. Lam, J. J., Jr., J. M. Stanley, C. M. Knott, and A. H. Knipling, G. Tamaki, 1. A. Onsager, and J. P. Hol- Baumhover. 1968. Suppression of nocturnal to- lingsworth were most helpful. J. U. McGuire, Jr. bacco insect popUlations with blacklight traps. Ibid., provided useful suggestions for analyzing the data. II: 611-2. L. Priddy prepared the graphs. Lawson, F. R., C. R. Gelllry, and J. M. Stunley. 1963. Effect of light traps on hornworm populations in large areas. USDA-ARS 33-91, 18 pp. REFERENCES CITED Levengood, W. C. 1969. Infrared method for deter- Burrett, J. R., Jr., H. O. Deay, and J. G. Hartsock. mining circadian patterns of carbon dioxide release. 1971. Reduction in insect damage to cucumbers, Z. Vergl. Physiologie 62: 153-66. tomatoes, and sweet corn through use of electric McFadden, M. W., and J. J. Lam, Jr. 1968. Influence light traps. J. Econ. Entomol. 64: 1241-9. of population level and trap spacing on capture of ClIntelo, W. W., J. S. Smith, Jr., A. H. BlIumhover, J. M. tobacco hornworm moths in blacklight traps with Stanley, and T. J. Henneberry. 1972a. Suppres- virgin females. J. Econ. Entomol. 61: 1150-2. sion of an isolated population of the tobacco horn- Onsager, J. A., and A. Day. 1973. Efficiency and ef- worm with blacklight traps unbaited or baited with fective radius of blacklight traps against southern virgin female moths. Environ. Entomol. I: 253-8. potato wireworm. Ibid., 66: 403--9. ClIntelo, W. W., J. S. Smith, Jr., A. H. Baumhover, J. M. Owen, D. F. 1969. Species diversity and seasonal Stanley, T. J. Henneberry, and M. B. Peace. 1972b. abundance in tropical sphingidae (Lepidoptera). The suppression of isolated populations of sphingids Proc. R. Entomol. Soc. London (A) 44: 162-8. by blacklight traps. Ibid., I: 753-9. Snow, J, W., R. L. Burton, A. N. Sparks, and W. W. Can- 1973a. Changes in the population levels of 17 insect telo. 1971. Attempted eradication of the corn ear- species during a 3 '12 year blacklight trapping pro- worm from St. Croix, U. S. Virgin Islands. USDA gram. Ibid .• 2: 1033-8. Prod. Res. Rep. 125. 12 pp. ClIntelo, W. W., A. H. Baumhover, T. J. Henneberry, and Snow, J. W., W. W. Cantelo, and G. C. Bowman. 1969. J. S. Smith, Jr. 1973b. Attempted suppression of Distribution of the corn eaTWorm on S1. Croix, U. the tobacco hornworm with sterile males. Ibid., 2: S. Virgin Islands and its relation to suppression pro- 48-54. gram. 1. Econ. Entomol. 62: 606-11. Deay, H. 0., J. G. Hartsock, and J. R. Barrett. 1963. Snow, J. W., W. W. CaDtelo, R. L. Burton, aDd S. D. Results on the use of light traps to control cucum- Hensley. 1968. Populations of fall armyworm, ber beetles. Proc. N. Centro Br. Entom. Soc. Am. corn eaTWorm, and sugarcane borer on St. Croix, 18: 37. U. S. Virgin Islands. Ibid., 61: 1757-60. Embody, D. R. 1971. Possible methods for measuring Sparks, A. N., R. L. Wrigbt, and J. P. Hollingsworth. the effective range of the sex-lure trap for the pink 1967. Evaluation of designs and installations of bollworm. USDA-ARS 81-43. 5 pp. electric insect traps to collect bollworm moths in Fennah, R. G. 1947. Insect pests of food crops in the Reeves County, Texas. Ibid., 60: 929-36. Lesser Antilles. Department of Agriculture Wind- Stanley, J. M., A. H. Baumbover, W. W. Cautelo, J. S. ward Islands, St. George, Grenada, B.W.I. 207 pp. Smith, Jr., M. B. Peace, aDd C. Asencio. 1971. A Gentry, C. R., F. R. Lawson, C. M. Knott, J. M. Stanley, population suppression experiment for tobacco horn- and J. J. Lam, Jr. 1967. Control of hornworms worms and other nocturnal insects using blacklight by trapping with blacklight and stalk cutting in traps on an isolated island, preliminary studies. North Carolina. J. Econ. Entomol. 60: 1437-42. USDA-ARS 42-193. 8 pp.