Conditioned taste aversion in the cricket Gryllus bimaculatus

Abstract

Conditioned taste aversion (CTA) is a form of classical conditioning in which animals associate the taste of a food with illness caused by toxin contained in the food. CTA in mammals is achieved with a long interval of up to several hours between food ingestion and illness induced by LiCl injection. Insects also exhibit CTA, but not much is known about its features. We investigated whether the cricket Gryllus bimaculatus exhibits CTA when ingestion of a sugar solution is followed by LiCl injection. Crickets that ingested sucrose solution 5-10 min before LiCl injection exhibited reduction of sucrose consumption tested 24 or 48 h after injection compared to that tested 24 h before injection. In contrast, crickets that ingested sucrose solution 5-10 min after LiCl injection or 1 h or 8 h before or after injection did not exhibit reduction of sucrose consumption, indicating that reduction of sucrose consumption by CTA training is pairing-specific. We conclude that CTA in crickets is similar to that in mammals in that one-trial pairing is sufficient to achieve memory retention for days, but it differs in that it is achieved with a relatively short interval (< 1 h) between food ingestion and toxin injection.

Figure 1

Experimental procedures for CTA training and testing in crickets. (A) A feeder used for the sugar consumption test. (B) CTA training to ingest 100 µl sugar solution followed by injection of 5 µl of 1 M LiCl solution. The amount of consumption of sugar solution for a given period of time was measured 24 h before CTA training and 24 or 48 h after CTA training.

Figure 2

Effects of injections of different concentrations of LiCl solution paired with sucrose consumption. (A) Kaplan–Meier plots of survival probabilities of three groups of crickets that received injection of different concentrations of LiCl solution. Crickets in all groups were allowed to consume 0.5 M sucrose solution for 2.5 min and they were injected 5 min later with 5 µl of saline (n = 50) or saline containing 1 M LiCl (n = 50) or 2 M LiCl (n = 54) solution. The probability of survival was measured at various times up to 48 h after injection. Dashed lines indicate 95% confidence interval. The log-rank test was used to compare survival probabilities of different groups. (B) Two groups of crickets were allowed to consume 0.5 M sucrose solution for 2.5 min (pre-test) and they were injected 5 min later with 5 µl of saline or saline containing 1 M LiCl. Sucrose consumption was tested again for 2.5 min 1 day after injection (post-test). The Wilcoxon test was used for statistical comparisons of amounts of sucrose consumption before and after the CTA training (*** P < 0.001, ns: not significant).

Figure 3

Effects of CTA training with different intervals between sucrose ingestion and LiCl injection. Five groups of crickets received an initial 2.5-min consumption test, and the next day they were allowed to ingest 100 µl of 0.5 M sucrose solution at various times before and after injection of LiCl. All of the groups received 2.5-min sucrose consumption at 24 h after LiCl injection. The Wilcoxon test was used for statistical comparisons of amounts of sucrose consumption before and after CTA training (**P < 0.01, ns: not significant).

Figure 4

Effects of CTA training with sucrose or fructose solution tested 2 days after LiCl injection. (A) Two groups of crickets received a 0.5 M sucrose consumption test, and the next day they were allowed to ingest 100 µm of 0.5 M sucrose solution 5–10 min or 8 h before LiCl injection. Their sucrose consumption was tested again 48 h after LiCl injection. (B) Another two groups received CTA training and testing with 1 M fructose solution. The Wilcoxon test was used for statistical comparisons of amounts of sugar consumption 24 h before and 48 h after CTA training (*P < 0.05, **P < 0.01, ns: not significant).