An Experimental Study on Colorado Potato Beetle Hibernation Under Natural Conditions

Summary

Here we present a method for studying Colorado potato beetle hibernation under the natural conditions of the temperate zone as well as a technique for collecting beetles in winter. This method allows to obtain a desired number of overwintering individuals for various analyses at any stage of hibernation.

Abstract

One of the major pests of potato Solanum tuberosum L. in the temperate zone is the insect Colorado potato beetle (CPB). Most studies on the immunity and diseases of the CPB are conducted during active feeding stages. Nonetheless, there are fewer studies on resting stages, although these beetles spend most of their life cycle in a state of winter diapause (hibernation). In this work, a method for investigating CPB hibernation under natural conditions was developed and tested, offering an opportunity to collect a sufficient number of individuals in winter. In this article, CPB survival was assessed, and infectious agents at different stages of hibernation were identified. CPB mortality increased during the hibernation, reaching a maximum in April-May. Entomopathogenic fungi (Beauveria, Isaria, and Lecanicillium) and bacteria Bacillus, Sphingobacterium, Peribacillus, Pseudomonas, and Serratia were isolated from the dead insects. The survival rate of the beetles for the entire hibernation period was 61%. No frozen or desiccated beetles were found, indicating the success of the presented method.

Introduction

The Colorado potato beetle Leptinotarsa decemlineata Say (CPB) is an important pest of Solanaceae plants, predominantly potato Solanum tuberosum L. The geographic range of this species is more than 16 million km² and constantly expands¹. The CPB has facultative winter diapause, and hibernation is obligatory in the temperate zone. The diapause is induced by a short-day photoperiod and modulated by temperature¹. These beetles overwinter in the adult stage by burrowing into soil. With increasing latitudes, the duration of the hibernation period extends. In the temperate zone, especially on north....

Protocol

1. Description of the cages for hibernation

NOTE: Depending on the aims of the experiment, the number of cages varies. Use at least three cages per sampling date. To estimate the number of beetles that will emerge, prepare at least three additional cages, which will not be taken out of the soil until spring.

1. Use cages made of a rigid wooden frame with a size of 25 × 25 × 40 cm (L × W × H).
2. To build a frame for the cage, use wooden slats at least 2 cm thick and 4 cm wide.
3. Cover the inside of the cage with a stainless-steel mesh having a size of openings ....

Results

The results below on overwintering CPBs show soil temperature, survival, and infections.

Soil temperature dynamics.
Temperatures below zero in the cages at a depth of 30 cm were registered from the end of November to the beginning of April (Figure 1). The average temperature during this period was minus 3.3 ± 0.1 °C (mean ± standard error). The lowest recorded temperature was minus 7.9 °C in mid-February.

Discussion

This study shows that the proposed method for studying the overwintering of CPBs enables us to obtain a sufficient number of insects in different periods of hibernation. The success of the presented technique depends on several independent factors, the most important of which is weather conditions. In a cold, snowless winter, the soil may freeze to the entire depth of the cage. In this case, the risk of death of all beetles goes up significantly¹⁸. The survival of the beetle depends on a combinati.......

Materials

Name	Company	Catalog Number	Comments
Agar-agar bacteriological purified	diaGene	1806.5000
Bile Esculin Agar	HiMedia	M972
Endo Agar	HiMedia	M029
Glucose monohydrate-D	PanReac Applichem	143140.1000Φ
Lactic acid	PanReac Applichem	141034.1211
Luria-Bertani liquid medium	HiMedia	G009
15 ml conical centrifuge tubes	Axygen	SCT-15ML-25-S
Peptone	FBIS SRCAMB	M030/O61
Phosphate buffered saline	Medigen	PBS500
Temperatutre and humidity datalogger Ecklerk-M-11	Relsib		Waterproof datalogger