Predators vary in their control of the diamondback moth

Three insect predators showed potential, dependent on the developmental stage, for the biological control of the diamondback moth Plutella xylostella. The study evaluated Eocanthecona furcellata, Hierodula patellifera and Paratenodera sinensis under laboratory conditions. The results indicated greater prey consumption at higher densities. They also showed superior performance in late immature stages and in adults, compared to the early stages of the predators.

The research analyzed the functional response of predators in different combinations of natural enemy stage, prey stage, and supply density. The authors tested larvae, pupae with cocoons, pupae without cocoons, and adults of Plutella xylostella. The study aimed to measure corrected prey consumption and classify functional response patterns using logistic regression and nonlinear models.

The trials with Eocanthecona furcellata involved second- to fifth-instar nymphs and adults. First-instar nymphs were not included in the tests, as previous observations indicate limited or inconsistent feeding at this stage. Predators received pupae of Tenebrio molitor before the fasting period. Then, they were exposed to different densities of larvae or pupae of Plutella xylostella for 24 hours.

In tests with Eocanthecona furcellata, corrected consumption increased with prey density. In adults fed second-instar prey, the average increased from 8,86 prey at density 10 to 75,81 prey at density 100. The study reports significant density effects across all combinations of predator and prey stages.

The results indicated a clearer response in more developed predators. In Eocanthecona furcellata, late instars and adults showed higher consumption and greater differentiation between densities. The authors associated this pattern with increased predatory capacity during development.

Mantidae

The mantids Hierodula patellifera and Paratenodera sinensis also showed increased consumption with higher prey density. The tests involved early instars, late instars, and adults. The prey consisted of third- and fourth-instar larvae and adults of Plutella xylostella. The fasting period used for mantids reached 48 hours, compared to 24 hours for Eocanthecona furcellata. Scientists consider this difference a limitation for direct comparisons between species.

In the classification of functional responses, type II patterns predominated. Among 37 combinations of predator-prey stages, 29 showed a response similar to type II, six showed a response similar to type III, and two were ambiguous. In Eocanthecona furcellata, 22 out of 25 combinations showed a type II curve. In Paratenodera sinensis, there was greater variation, with three responses similar to type III.

Handling prey

Interpreting the parameters required caution. Prey handling time was poorly identified in many models. Only one of the 37 combinations generated an estimate considered stable for this parameter. Therefore, the authors warn against comparisons based solely on maximum predation capacity.

Direct comparisons between species received limited analysis. Researchers restricted this step to the fourth instar of prey, the second and third instars of predators, and densities of 10, 20, and 30. Within this subset, Eocanthecona furcellata consumed less prey than the two mantids in the second instar. In the third instar, this pattern ceased to occur consistently. At some densities, Eocanthecona furcellata overcame Hierodula patellifera and Paratenodera sinensis.

Differences and stages

Scientists conclude that differences between predators depend on the stage of development being compared. Aggregate assessment by species may distort the potential for control. The developmental stage of the natural enemy and prey should guide predator selection and release timing in biological control strategies.

From an applied perspective, mantises showed higher per capita larval consumption under certain laboratory conditions. This suggests potential for rapid suppression of larval populations at high densities. Eocanthecona furcellata, on the other hand, it attacked different stages of the pest, including pupae with and without cocoons. This behavior may offer complementary value in management programs.

More information at DOI 10.3390/insects17050490