Tracing dietary origins of aphids and the predatory beetle Propylea japonica in agricultural systems using stable isotope analyses

Abstract

Tracing dietary origins of the predatory beetle Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) aids understanding their roles in the food web and provides information to develop strategies for effective conservation in agroecosystems comprised of wheat [Triticum aestivum L. (Poaceae)], cotton [Hirsutum spp. (Malvaceae)], and maize [Zea mays L. (Poaceae)]. Intrinsic markers of carbon and nitrogen stable isotope ratios (δ13C and δ15N) in P. japonica need to be developed to ascertain the source(s) of diet. Experiments were carried out to examine the changes of δ13C and δ15N among the three crops, pests (wheat, cotton, and maize aphids; all Hemiptera: Aphididae), and P. japonica fed on aphids of each of the three crops. Results indicated that δ13C values in P. japonica fed on wheat, cotton, and maize aphids were −27.2 to −26.5‰, −24.2 to −23.9‰, and −11.0 to −10.7‰, respectively, whereas their δ15N values were 1.1 to 2.9‰, 6.0 to 7.4‰, and −0.6 to 0.1‰, respectively. δ13C and δ15N plots clearly identify the three crops, the dietary origins of the aphids, and the host origins of the aphid prey consumed by the ladybird beetles, as each pathway displays a non‐overlapping pattern. Based on the values of δ13C and δ15N of the three food webs, dietary origins can be traced in the predatory beetle P. japonica derived from wheat, cotton, and maize crops.

Variable Isotopic Compositions of Host Plant Populations Preclude Assessment of Aphid Overwintering Sites

“…Soybean aphid 13 C and 15 N values were significantly positively correlated with those of their host plants ( Figure 2 a), being slightly enriched (slope = 1.1), on average, relative to the plant in terms of 15 N, and depleted (slope = 0.8) in terms of 13 C. Previous studies have also found scaling of bulk 15 N between aphids and host plants, though the direction of scaling varies among studies [ 24 , 36 , 37 , 38 , 39 ]. Importantly, the observed signal of isotopic congruence between the soybean aphids and buckthorn host plants suggests stable isotopes, particularly 15 N, could be used to distinguish the origins of spring colonizers of soybean.…”

“…For example, geographic variation in stable isotope composition of deuterium and 13 C has been utilized to make inferences about monarch butterfly ( Danaus plexippus L.) migration from overwintering sites in Mexico to summer habitats across a broad expanse of North America [ 18 , 19 ]. Within agricultural landscapes, variation in diet revealed by stable isotopes of 13 C and 15 N has been used to track movement of herbivores and predators among crop types [ 20 , 21 , 22 , 23 , 24 ]. The stable isotope composition of an organism derives from (1) the maternal contribution to its biomass; (2) the isotopic compositions of the proteins, lipids, water, and sugars in its diet; (3) N-turnover within the organism; (4) energy demands of the organism; and (5) background isotopic signatures, as a function of latitude/longitude, altitude, humidity, habitat type, and the myriad random effects of life in a heterogeneous landscape [ 25 , 26 , 27 ].…”

Natal origin of the invasive biosecurity pest, brown marmorated stink bug (Halyomorpha halys: Penatomidae), determined by dual‐element stable isotope‐ratio mass spectrometry

“…Hitherto, there has been little research on stable isotopes as provenance markers in sap‐sucking insects (e.g. ) and none on the family Pentatomidae. Of note is that the intra‐population δ 2 H variation was less than observed for other entomological isotope studies and the intra‐country variation was generally consistent across the reference data‐set.…”

Trophic ecology of citrus pests based on stable isotope analysis

“…According to Ye et al (2014), peanut was a more effective refuge to sustain Bt-susceptible bollworm individuals and reduce the risk of development of a Btresistant biotype. Ouyang et al (2015) traced dietary origins of the predatory beetle Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) based on the values of δ 15 N and δ 13 C, in order to understand their roles in the food web and provide information to develop strategies for effective conservation in agroecosystems.…”