Intraguild Prey Served as Alternative Prey for Intraguild Predators in a Reciprocal Predator Guild between Neoseiulus barkeri and Scolothrips takahashii

Abstract

The predatory mites Neoseiulus barkeri (Hughes) and the predatory thrips Scolothrips takahashii (Priesner) are known as potential biocontrol agents for the two-spotted spider mite Tetranychus urticae (Koch). These two predator species occur simultaneously on crops in agricultural ecosystems and are proved to be involved in life-stage specific intraguild predation. The intraguild prey may play a role in securing the persistence of the intraguild predators during food shortage periods. To understand the potential of intraguild prey as food source for intraguild predators in the N. barkeri and S. takahashii guild at low T. urticae densities, the survival, development and reproduction of both predators was determined when fed on heterospecific predators. The choice tests were conducted to determine the preference of the intraguild predator between the intraguild prey and the shared prey. Results showed that 53.3% N. barkeri and 60% S. takahashii juveniles successfully developed when fed on heterospecific predators. Female intraguild predators of both species fed on intraguild prey survived and laid eggs throughout the experiment. In the choice test, both intraguild predator species preferred their extraguild prey T. urticae. This study suggested that intraguild prey served as an alternative prey for intraguild predators prolonged survival and ensured the reproduction of intraguild predators during food shortage, ultimately decreasing the need for the continual release of the predators.

Keywords: intraguild predation; predatory mites; predatory thrips; prey preference; reproduction; survival.

Figure 1

Cumulative survival rates of immature Neoseiulus barkeri (A) and Scolothrips takahashii (B) fed with intraguild prey (S. takahashii first instar larva served as intraguild prey for N. barkeri, N. barkeri egg served as intraguild prey for S. takahashii), extraguild prey (Tetranycus urticae protonymph), or no food. T. u: T. urticae; S. t: S. takahashii; N. b: N. barkeri; N1: protonymph; L1: first instar larva; E: egg. The cumulative survival rates of intraguild predators under different types of diet were compared with Kaplan–Meier survival analysis using Log-rank tests (p < 0.05).

Figure 2

Cumulative survival rates of female Neoseiulus barkeri and Scolothrips takahashii subject to no food. N. b: N. barkeri; S. t: S. takahashii; F: female.

Figure 3

The oviposition (mean ± SE) of females of Neoseiulus barkeri (A) and Scolothrips takahashii (B) when offered intraguild prey (S. takahashii first instar larva served as intraguild prey for N. barkeri female, N. barkeri egg served as intraguild prey for S. takahashii female) and extraguild prey (Tetranychus urticae protonymph). T. u: T. urticae; S. t: S. takahashii; N. b: N. barkeri; N1: protonymph; L1: first instar larva; E: egg. T-test for independent samples was used to measure the oviposition per female per day in different diets (p < 0.05). The arrow points to the time at which all predators resumed the ability to lay eggs.

Figure 4

Preference experiments. Attack frequencies of Neoseiulus barkeri (A) and Scolothrips takahashii (B) on intraguild prey (S. takahashii first instar larva served as intraguild prey for N. barkeri female, N. barkeri egg served as intraguild prey for S. takahashii female) and extraguild prey (Tetranychus urticae protonymph). Attack 1, 2, 3 and total were calculated as the proportion of intraguild predator first attack, second attack, third attack and the sum of these three attacks on a specific prey. Theoretical response represents no prey preference by the intraguild predator for each specific prey (theoretical index of 50%). T. u: T. urticae; S. t: S. takahashii; N. b: N. barkeri; N1: protonymph; L1: first instar larva; E: egg. Red areas show predation on the T. urticae, blue areas show predation on intraguild prey. Asterisks indicate a significant prey preference (χ², p < 0.05).