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 popu- lations 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. por- toricensis (Smyth), Calosoma alternans alternans (F.), Conoderus sp. and Lacon sub- costatus (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 popula- tions. 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 collec- tions. 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.