Improvement of quarantine techniques for detecting early-stage Callosobruchus maculatus Fabricius

Callosobruchus maculatus Fabricius is a quarantine pest for imported plants and agricultural plants in China, posing a severe threat to the safety of stored beans. Despite the availability of various detection methods, they are insufficient in terms of detection accuracy and operational simplicity, and they focus only on larvae, pupae, and adults, lacking a detection method for eggs, which can lead to missed identifications. This study addresses the issue of lightly infested beans failing to float in the conventional flotation method (using saturated NaCl solution), and the absence of an effective egg detection method. We aimed to optimize the quarantine detection methods for larvae and eggs of C. maculatus and provide support for improving quarantine accuracy.

The flotation characteristics of mung beans were compared in saturated NaCl and CaCl₂ solutions to determine the optimal detection solution and concentration. Meanwhile, five common types of beans (mung beans, peas, soybeans, broad beans, and chickpeas) were selected and immersed in 1%, 5%, 10%, and 20% Tween 80 solutions, and different soaking time gradients were set to compare the elution rates of C. maculatus eggs from the grain surface of each treatment group.

Using a 1.35 g/cm³ CaCl₂ solution enhanced detection rates, particularly for early-instar larvae, advancing the earliest detection time to 24 hours after initial larval infestation. Furthermore, all concentrations of Tween 80 solution demonstrated certain efficiency, but the elution rates varied with bean type and immersion duration. Specifically, after 4 hours of immersion in 5% Tween, 80%~85% of egg masses detached from mung beans and peas, approximately 60% from soybeans and broad beans, but only 35% from chickpeas.

These findings suggested that floating beans in a 1.35 g/cm³ CaCl₂ solution was an effective method for detecting mung beans lightly infested by C. maculatus larvae, while 5% Tween (immersion for 4 hours) was more effective for detecting eggs of C. maculatus on mung beans and peas. The research results provided valuable insights for optimizing current quarantine techniques for C. maculatus.