Pharmacophagy in green lacewings (Neuroptera: Chrysopidae: Chrysopa spp.)?

Jeffrey R Aldrich,Qing-He Zhang,Kamal Chauhan

doi:10.7717/peerj.1564

Abstract

Green lacewings (Neuroptera: Chrysopidae) are voracious predators of aphids and other small, soft-bodied insects and mites. Earlier, we identified (1R,2S,5R,8R)-iridodial from wild males of the goldeneyed lacewing, Chrysopa oculata Say, which is released from thousands of microscopic dermal glands on the abdominal sterna. Iridodial-baited traps attract C. oculata and other Chrysopa spp. males into traps, while females come to the vicinity of, but do not usually enter traps. Despite their healthy appearance and normal fertility, laboratory-reared C. oculata males do not produce iridodial. Surprisingly, goldeneyed lacewing males caught alive in iridodial-baited traps attempt to eat the lure and, in Asia, males of other Chrysopa species reportedly eat the native plant, Actinidia polygama (Siebold & Zucc.) Maxim. (Actinidiaceae) to obtain the monoterpenoid, neomatatabiol. These observations suggest that Chrysopa males must sequester exogenous natural iridoids in order to produce iridodial; we investigated this phenomenon in laboratory feeding studies. Lacewing adult males fed various monoterpenes reduced carbonyls to alcohols and saturated double bonds, but did not convert these compounds to iridodial. Only males fed the common aphid sex pheromone component, (1R,4aS,7S,7aR)-nepetalactol, produced (1R,2S,5R,8R)-iridodial. Furthermore, although C. oculata males fed the second common aphid sex pheromone component, (4aS,7S,7aR)-nepetalactone, did not produce iridodial, they did convert ∼75% of this compound to the corresponding dihydronepetalactone, and wild C. oculata males collected in early spring contained traces of this dihydronepetalactone. These findings are consistent with the hypothesis that Chrysopa males feed on oviparae (the late-season pheromone producing stage of aphids) to obtain nepetalactol as a precursor to iridodial. In the spring, however, wild C. oculata males produce less iridodial than do males collected later in the season. Therefore, we further hypothesize that Asian Chrysopa eat A. polygama to obtain iridoid precursors in order to make their pheromone, and that other iridoid-producing plants elsewhere in the world must be similarly usurped by male Chrysopa species to sequester pheromone precursors.

Highlights

With ~ 6000 living species, Neuroptera is one of the smaller orders of insects (Winterton et al.2010), but most larval neuropterans are predacious, often in agricultural systems, lending added importance to this group (Tauber et al 2009)
Analyses of C. oculata revealed that nonanal and nonanol were abundant in extracts of the abdominal sternites of males regardless of whether they were collected in the wild or reared in the laboratory; iridodial was absent in extracts of laboratory-reared C. oculata males (Fig. 3A and B; Table 1)
Rearing C. oculata males in isolation from conspecific males did not result in production of iridodial (Table 1), and removing the antennae of C. oculata males had no affect on production of iridodial (Supplemental Figure 2)

Summary

Introduction

With ~ 6000 living species, Neuroptera is one of the smaller orders of insects (Winterton et al.2010), but most larval neuropterans are predacious, often in agricultural systems, lending added importance to this group (Tauber et al 2009). Green lacewings (Chrysopidae) are the most agriculturally important of the neuropterans because their larvae are generalist predators that actively hunt for aphids, mites, whiteflies, caterpillars, and other small, soft-bodied prey that are common pests on horticultural plants, and in field and tree crops (McEwen et al 2007). While most chrysopids are predacious as adults, species in the genus Chrysoperla feed on nectar and pollen, a characteristic that led to development of artificial diets and mechanized mass rearing of some species (McEwen et al 2007; Nordlund et al 2001). Many other lacewings whose adults are predacious are naturally important in agricultural systems, most notably Chrysopa species, but efforts to develop artificial diets or lures for these species have been largely unsuccessful (McEwen et al 2007). Pheromones are potentially useful for attracting generalist predators for augmentative and conservation biological control

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