Suboptimal nutrient balancing despite dietary choice in glucose-averse German cockroaches, Blattella germanica Kim Jensen ⇑ , Coby Schal, Jules Silverman Department of Entomology and the W.M. Keck Center for Behavioral Biology, North Carolina State University, Raleigh, NC 27695-7613, USA article info Article history: Received 8 May 2015 Received in revised form 24 June 2015 Accepted 1 July 2015 Available online 2 July 2015 Keywords: Carbohydrate Deterrence Geometric framework Glucose aversion Gustatory functioning Oocyte development Optimal foraging Protein Taste adaptation Toxin avoidance abstract Insects have evolved fine-tuned gustatory and post-ingestive physiological mechanisms that enable them to self-select an optimal composition of macronutrients. Their ability to forage optimally among multiple food sources and maximize fitness parameters depends on their ability not only to taste and perceive the nutritional value of potential foods but also to avoid deleterious components; the strength of such avoid- ance should reflect the severity of the perceived hazard. In German cockroaches (Blattella germanica), glucose aversion has evolved in some populations in response to anthropogenic selection with glucose-containing insecticidal baits. In four feeding treatments, we gave newly eclosed glucose-averse female cockroaches free choice to feed from two artificial, nutritionally complementary foods varying in protein and carbohydrate composition, with glucose or fructose as the sole carbohydrate source in either food. After 6 days of feeding, we measured diet consumption and the length of basal oocytes as an estimate of sexual maturation. The females did not compromise on their aversion to glucose in order to balance their protein and carbohydrate intake, and experienced lower sexual maturation rates as a consequence. Nutrient specific hunger via feedback mechanisms, and adjustments to gustatory sensitiv- ity thus do not override the deterrence of glucose, likely due to strong selection against ingesting even small amounts of toxin associated with glucose in baits. In the absence of baits, glucose aversion would be expected to incur a fitness cost compared to wild-type individuals due to lower overall food availability but also to larger difficulty in attaining a nutritionally balanced diet. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction A wide range of animals, spanning from herbivores to omni- vores and predators, have been shown to forage optimally for specific nutrients when allowed to compose a balanced diet from nutritionally complementary food sources (Behmer, 2009; Fanson et al., 2009; Lee et al., 2008; Jensen et al., 2012, 2013; Raubenheimer and Jones, 2006; Simpson et al., 2004, 2015). In particular, omnivores that scavenge in nutritionally heterogeneous environments are faced with the challenge of composing an overall balanced diet from food sources that may vary widely in nutri- tional composition, quality and availability. In order to do so, ani- mals have evolved highly sensitive chemosensory and internal feedback mechanisms that enable them to sense what specific nutrients they need, and to be stimulated to consume them (Simpson and Raubenheimer, 1993, 1996; Simpson et al., 1991). However, little is known about how the evolution of optimal nutri- ent balancing mechanisms interacts with mechanisms of deterrence and toxin avoidance, which function to prevent the ingestion of lethal or deleterious compounds. The effects of food deterrents on nutrient balancing are rela- tively well studied in herbivorous insects (Behmer et al., 2002; Bernays and Raubenheimer, 1991; Hägele and Rowell-Rahier, 1999; Raubenheimer, 1992; Simpson and Raubenheimer, 2001; Singer et al., 2002), but nutrient balancing and performance in relation to potentially lethal toxins has only been investigated very recently (Archer et al., 2014; Schmehl et al., 2014; Shik et al., 2014). Whereas deterrents typically stop the forager from eating before detrimental toxin doses are ingested (Chapman, 2013; Ozaki et al., 2003), toxins that are coupled with phagostimulating nutrients to disguise their taste and facilitate consumption would require highly sensitive gustatory reception capabilities. The German cockroach (Blattella germanica Linnaeus) is an extreme generalist omnivore and a widespread pest in human establishments, where it is apparently able to compose a nutrition- ally balanced overall diet from various food objects within a house- hold (Jones and Raubenheimer, 2001; Schal, 2011; Schal et al., 1984). German cockroach nymphs have been shown to grow slower when restricted to nutritionally deficient or imbalanced http://dx.doi.org/10.1016/j.jinsphys.2015.07.001 0022-1910/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: kjensen@ncsu.edu (K. Jensen). Journal of Insect Physiology 81 (2015) 42–47 Contents lists available at ScienceDirect Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys