Effects of Bt Crops on Nontarget Invertebrates under Large Scale Crowing Conditions Long Term Studies

Nontarget Community3

Natural Enemies Arthropod predators Arthropod predators Australian arthropods

Arthropod predators Arthropods

Foliage

Arthropods Ground Beetles Springtails

Bt Crop

Cotton Cotton

Cotton

Cotton

Corn

Corn

Corn

Corn Corn

Study Length (Years)

Cry Protein

CrylAc CrylAc

CrylAc

CrylAc & CrylAc+ Cry2Ab CrylAb

CrylAb +

VIP3A

Cry3Bb

Cry3Bb Cry3Bb

Significant Adverse Effects

None None

None

None

Someb

None

None None

Reference

Naranjo, 2005112,113 Head et al., 2005114

Torres and Ruberson, 2005ll5

Whitehouse et al., 2005116

Pilcher et al., 2005117

None Dively, 20051

Bhatti et al., 2005120

Bhatti et al., 2005121 Bitzer et al., 2005122

a Each study varied in the number of species monitored, but in general each study sampled a large number of species, typically more than 30. b Populations of the hymenopteran endoparsitoid (Macrocentrus cingulum), which is dependent on the target pest, the European corn borer (Ostrinia nubilalis), declined, as expected, along with its host.

effects were detected in most of these populations over the five- to six-year period of these studies (Figure 3.4). Minor reductions were observed in a few nontarget species, apparently as a result in the reduction of pink bollworm populations. In contrast, large and long-lasting negative effects were observed on numerous nontarget invertebrate populations in both conventional cotton and CrylAc cotton treated with the chemical insecticides buprofezin, pyriproxyfen, and oxamyl. The overall conclusion of these multiyear studies was that there "were essentially no effects of Bt cotton on natural enemy function"112 in Arizona cotton populations.

In the above studies, there was only one principal lepidopteran pest, the pink bollworm, P. gossypiella. In other cotton-growing regions of the United States, such as states in the southeast, there are often multiple lepidopternan pests, including H. virescens, H. zea, S. exigua, and S. frugiperda. In these areas, CrylAc cotton is effective against H. virescens but often not effective against other lepidopteran pests, necessitating the periodic use of chemical insecticides. This makes the economic and environmental analysis of the efficacy of CrylAc cotton more complex. With respect if) »

2001

2002

2003

All Years

2001

2002

2003

All Years

Prédation Dislodge Parasitism Prédation Dislodge Parasitism Prédation Dislodge Parasitism Prédation Dislodge Parasitism

Prédation Dislodge Parasitism Prédation Dislodge Parasitism Prédation Dislodge Parasitism Prédation Dislodge Parasitism

FIGuRE 3.4 Comparison of predator and parasite populations that prey on the white fly (Bemesia tabaci) in non-Bt and CrylAc Bt cotton from 2001-2003. No significant differences were observed over the three-year period between predator and parasite populations on these crops (see Naranjo, S., Long-term assessment of the effects of transgenic Bt cotton on the abundance of nontarget arthropod natural enemies, Environ. Entomol, 34, 1193, 2005; and Naranjo, S., Long-term assessment of the effects of transgenic Bt cotton on the function of the natural enemy community, Environ. Entomol, 34, 1121, 2005).

to nontarget populations, though these may not be affected by Bt cotton, populations will typically decline when treated with chemical insecticides. So the question arises as to whether there are environmental benefits of using Cry1Ac cotton in regions with a complex of pests.

To test this, a three-year study was carried out in large commercial plantings of Cry1Ac cotton in Alabama, Georgia, and South Carolina during 2000-2002.114 Key nontarget beneficial invertebrate populations, including predaceous beetles, heter-opterans, lacewings (again including C. perla), the fire ant (Solenopsis invicta), and spiders were monitored and compared in conventional and Cry1Ac cotton. When needed, chemical insecticides were applied, the principal ones being spinosad, pyre-throids (cyhalothrin, cypermethrin), and an organophosphate (dicrotophos). The results of this study showed that both the primary target pest, H. virescens, and other lepidopteran pests were reduced in the Cry1Ac cotton fields, therefore requiring fewer chemical insecticide applications compared to conventional cotton. On average, across the geographical regions tested, the need for chemical insecticide applications was reduced by about half in the Cry1Ac cotton plots (from 0.3 to 4 in conventional cotton, to 0 to 2.8 in Cry1Ac cotton). Reduction in the number of chemical insecticide applications in the Cry1Ac cotton reduced the impact of using insecticide sprays, yielding a higher abundance of nontarget invertebrates in these fields compared to conventional cotton. This study suggests that the use of Bt cotton in areas where there are multiple pests can still be of benefit to the environment, and specifically to nontarget populations, as a result of reductions in the use of chemical insecticides. However, the extent of the benefit will clearly depend on the pest species complex, which can vary from one year to another. New lines of Bt cotton coming to market that produce two or more insecticidal proteins will likely be more effective in controlling the other lepidopteran pests, resulting in increased environmental benefits.

In a another study carried out in Georgia (U.S.) from 2002 to 2004, the effects of Bt cotton and non-Bt cotton on canopy- and ground-dwelling predatory arthropods were compared.115 In the test fields, which varied from 5 to 15 hectares in size, standard grower practices were used, meaning that pest populations, including stink bugs, were monitored and treated with insecticides when necessary. A variety of insecticides were used, including spinosad, two pyrethroids, and aldicarb. To summarize the results of this study, the authors concluded that Bt cotton (Cry1Ac) had no "negative impact" on predator populations over the three-year period of the study when used in conjunction with standard grower practices, thus supporting the findings of the above study carried out in the southeastern United States.114

In a study carried out in Australia during a three-year period from 1995/1996 to 1997/1998, two different types of Bt cotton (Cry1Ac cotton and a stacked cotton that produces Cry1Ac plus Cry2Aa) were compared to nonsprayed conventional cotton and cotton sprayed with chemical insecticides in commercial fields of cot-ton.116 The arthropods monitored included the pest species Heliocoverpa and a wide variety of other nontarget arthropod groups containing many species of mites, ants, aphids, parasitic wasps, bees, beetles, flies, true bugs, and spiders. A major impact on the arthropod communities was noted in the cotton fields sprayed with chemical insecticides, with only minor differences observed between Bt cotton and non-Bt

FIGuRE 3.5 Effects on Bt and non-Bt cotton on arthropod communities in commercial fields in Australia over three years. The straight line (white circles) represents nonsprayed conventional (control); black circles are conventional sprayed cotton; grey squares are Cry1Ac cotton; and grey triangles are stacked Bt cotton (Cry1A + Cry2A). See Whitehouse, M.E.A., Wilson, L.J., and Fitt, G.P., A comparison of arthropod communities in transgenic Bt and conventional cotton in Australia, Environ. Entomol., 34, 1224, 2005 for details.

FIGuRE 3.5 Effects on Bt and non-Bt cotton on arthropod communities in commercial fields in Australia over three years. The straight line (white circles) represents nonsprayed conventional (control); black circles are conventional sprayed cotton; grey squares are Cry1Ac cotton; and grey triangles are stacked Bt cotton (Cry1A + Cry2A). See Whitehouse, M.E.A., Wilson, L.J., and Fitt, G.P., A comparison of arthropod communities in transgenic Bt and conventional cotton in Australia, Environ. Entomol., 34, 1224, 2005 for details.

conventional cotton (Figure 3.5). The largest difference between the Bt cotton and non-Bt cotton was in the presence of Helicoverpa spp. pests. However, the authors also found a slightly higher abundance of certain fly species and true bugs in the conventional cotton compared to the Bt cotton. As it is anticipated that the percentage of Bt cotton (particularly stacked Bt cotton) will increase in Australia over the next few years, the authors cautioned that nontarget arthropod populations should continue to be monitored to determine whether there will be any long-term effects on these populations.

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