Conservation of Predatory Carabid Beetles (Coleoptera: Carabidae) in agroecosystems of the Southern Great Plains
Stable carbon isotope data can elucidate carabid dispersal powers, habitat utilization, and the impact of tillage on carabid beetle populations in diverse agroecosystems in the Southern Great Plains. Based on early season isotope data from crops, host-specific aphids and carabid beetles there was significant carabid dispersal from the semi-permanent refuge alfalfa to sorghum an annual crop. Isotope data is supported by physical data from trapping locations. More carabid beetles were trapped in no-till sorghum than in conventionally tilled sorghum during the growing season. Significant differences in habitat selection were more discernable at the genera level for the target carabids.
It has been noted that carabids are an important component of natural enemy assemblages consuming agricultural pests. Through the use of pitfall trapping and stable carbon isotope analyses the relationship of carabid dispersal and prey consumption can be better understood (Teeri and Schoeller 1979, Peterson and Fry 1987, Ostrom and Fry 1993).
The first objective has been completed:
1. Quantify carabid colonization of annual crops (sorghum/winter wheat) from a semi-permanent habitat (alfalfa) as it relates to disturbance (tillage);
The second objective is in process.
2. Elucidate carabid dispersal powers through prey selection, diet changes within and among habitats, and larval habitat utilization;
The third objective will begin after data analysis.
3. Provide results of this research to producers and IPM professionals.
Objective 1: I have evaluated colonization of sorghum (conventional tillage vs. no-till) by carabids from a semi-permanent refugia habitat (alfalfa). Using standard pitfall traps spaced at specific distances within sorghum strips, we were able to calculate distances traveled over time for targeted carabid species.
Objective 2: I will elucidate the dispersal power of carabids between a semi-permanent refugia habitat (alfalfa) and an annual crop (sorghum) using stable carbon isotope analyses. This data coupled with results from objective one will be used to estimate carabid dispersal power among habitats and will be used to determine natal origins and therefore source of refuge.
Objective 3: Results from this study will be presented to producers and IPM professionals via extension publications, research journals, field days, and presentations at professional meetings.
During 2009, work continued on sample preparation and shipment for stable carbon isotope processing (SCIP). Examination of carabid dispersal based on carbon isotope ratios can only be done within systems with distinct 13C sources. Alfalfa, a C3 plant and sorghum, a C4 plant, have distinctly different carbon isotope ratios that provide a predictive relationship as 13C depletion or enrichment occurs. Preparation and shipment of an additional 23 plant samples has been completed. Isotope data has been returned for 6 of those plant samples. Alfalfa and sorghum isotope ratios continue to be within expected values for C3 (-20 to -35 0/00) and C4 (-9 to -19 0/00) plants.
In Oklahoma, four aphid species found only in alfalfa include the spotted alfalfa aphid (Therioaphis maculate), pea aphid (Acyrthosiphon pisum), blue aphid (Acyrthosiphon kondoi), and the cowpea aphid (Aphis craccivora). Aphid sampling in alfalfa during 2006 and 2007 found that blue and pea aphids were the most abundant. The corn leaf aphid (Rhopalosiphum maidis) and the green bug (Schizaphis graminum) are found on sorghum but not alfalfa in Oklahoma. The corn leaf aphid was the only species found and collected in sorghum during 2006 and 2007. Once the aphids were identified to species they were combined by species, location, and date to provide sufficient sample material for processing. Data has been returned on 12 of 97 host-specific aphid samples sent for isotope processing. Aphid isotope ratios consistently reflect the isotopic composition of the plant type, C3 or C4, from which they were collected.
Eight common cropland species of carabids: Cratacanthus dubius, Cyclotrachelus torvus, Pasimachus elongatus, Poecilus chalcites, Scarites subterraneus, Cicindela punctulata, Tetracha virginica, and Calosoma affine, were collected during previous sampling and are being used for isotope investigation. All eight of these species are predators within the agroecosystems of the Southern Great Plains. Dissection of 2006 carabids into subsamples has continued and as a result 12 of 21 sampling days have been completed. The dissections for 2007 carabids were started in February and 9 of 19 sampling days are now complete. A total of 1576 carabid tissue subsamples were shipped for stable carbon isotope processing. Data has been returned for 768 beetle samples. Preliminary data analysis has begun for 2006.
In June 2006, dispersal of 325 target carabids was analyzed based on their SCIR (See Figure 1). Isotope data provided evidence that 226 carabids moved from alfalfa to sorghum and six moved from sorghum to alfalfa. This trend indicates that semi-permanent alfalfa is being used as a refuge during the early stages of soil preparation (tillage) and planting of sorghum. This SCIR data revealed that 43 carabids didn’t move from alfalfa and 16 carabids didn’t move from sorghum. Dispersal for 34 carabids was undetermined due to isotope ratios in the range of -180/00 to -20 0/00, which may indicate diet mixing. Based on SCIR, one beetle, Pasimachus elongates, (CA66236) demonstrated diet switching. Beetle CA66236 had a SCIR of -15.760/00 in its metabolically inactive tissue subsample which is more similar to sorghum, C4 (-9 to -19 0/00). These tissues retain past dietary intake. Recent dietary intake is represented in Beetle CA66236’s metabolically active tissue subsample which had a SCIR of -22.170/00 and this is more similar to alfalfa, C3 (-20 to -35 0/00). Beetle CA66236 was trapped in alfalfa which supports the isotope data demonstrating movement from sorghum to alfalfa.
Habitat utilization and the impact of tillage on carabid adult and larvae were analyzed for 2006 and 2007. There was a total of 1,354 beetles trapped of which 561 were caught in 2006 and 793 were caught in 2007. There were more beetles trapped in no-till (NT) for both years (n=361, mean = 25.79) than there were in conventional tillage (CT), (n=272, mean =19.43). In 2006, 142 beetles were trapped in NT, 134 in CT and 285 in the adjacent alfalfa. In 2007, 219 beetles were trapped in NT, 138 in CT, and 436 in adjacent alfalfa field. There was insufficient larval data in 2006 to analyze. A total of 255 larvae were collected in 2007. There were 107 larvae trapped in alfalfa and 148 trapped in sorghum strips. Within these strips, 74 larvae were trapped in NT and 74 in CT.
There was a significant difference in habitat selection by two genera Calosoma and Tetracha in both years. In 2006, there were 52 Calosoma beetles trapped in alfalfa compared to zero trapped in CT. This genus had 235 beetles collected in alfalfa compared to seven in CT in 2007. For the genus Tetracha there were 51 individuals trapped in alfalfa compared to 16 in the CT in 2006. In 2007, Tetracha had 87 beetles collected in alfalfa compared to zero in CT.
There was no difference between NT and CT in 2006 for adult carabids (See Graph 1). Throughout the 2006 season, the genera Pasimachus (n=7) and Cyclotrachelus (n=4) had very low numbers of beetles collected in sorghum. The genus Calosoma was not collected in sorghum until September 2006 (n=6).These small sample sizes and a lack of a discernable habitat preference for CT or NT could have been in response to the severe drought conditions during 2006.
In 2007, the overall trend indicated a preference for NT in all target genera (See Graph 2). Sorghum was planted in late May of 2007 and in June the genera Cicindela, Cratacanthus, Cyclotrachelus, and Scarites had fewer adults trapped in CT compared to NT. These results support the conclusion that NT is more favorable to carabids than CT in this location. Only two genera, Cicindela and Tetracha, showed a month-by-month increase in the number of individuals collected in CT after planting. This may demonstrate a recovery trend in CT as conditions stabilize over time.
The sorghum strips interfaced with alfalfa, thereby providing carabids with the opportunity to utilize alfalfa as a refuge from CT. In June 2007, the number of carabid larvae trapped in alfalfa compared to CT indicates alfalfa was used as a refuge from disturbance regimes (See Graph 3). Data from July reflects a rebound in larvae presence in NT and CT as conditions normalized. Larvae numbers demonstrated a recovery trend in CT over time (See Graph 3). Overall, carabid adults and larvae tended to prefer NT over CT in 2007. A recovery trend was demonstrated by carabid larvae and adults of two genera over time after CT.
Impacts and Contributions/Outcomes
Results from this study will be communicated to producers and IPM professionals through extension fact sheets and publication in a scientific journal (e.g. Journal of Economic Entomology, Journal of Ecological Entomology). These data will be presented at county field days when complete. A poster was presented about the effects of no-till and conventional till on carabid adult and larval dispersal at the 2009 Southwestern Branch meeting of the Entomological Society of America, Stillwater, Oklahoma in February 2009. An oral presentation was given on the early stable carbon isotope data elucidating carabid dispersal at the National Entomological Society meeting, Indianapolis, Indiana in December 2009. This research project will be available as a dissection publication when completed.
Oklahoma State University
127 Noble Research Center
Stillwater, OK 74078
Office Phone: 4057446298