Evaluating the Effect of Pesticides on the Larvae of the Solitary Bees

Summary

The present protocol explains a method to feed pesticide-contaminated provisions to the larvae of the solitary bees, Osmia excavata. The procedure examines the ecotoxicity of the pesticide to the larvae of the solitary bees.

Abstract

Current ecological risk assessments of pesticides on pollinators have primarily considered only laboratory conditions. For the larvae of solitary bees, ingestion of provisions contaminated with pesticides may increase the mortality rate of the larvae, decrease the collection rate and the population of adult solitary bees in the next year from a demographic perspective. But there are limited studies on the effects of pesticides on the larvae of solitary bees. Therefore, understanding how pesticides influence the larvae of solitary bees should be considered an integral part of pesticide ecological risk assessment. This study presents a method to expose the larvae of solitary bee, Osmia excavata, to lethal or sublethal doses of pesticide, tracking larval weight gain, developmental duration, eclosion ability, and food consumption efficiency conversion of ingested food. To demonstrate the effectiveness of this method, the larvae of O. excavata were fed with provisions containing acute lethal and sublethal doses of chlorpyrifos. Then, the above indexes of the treated larvae were investigated. This technique helps to predict and mitigate the risk of pesticides to pollinators.

Introduction

Pollinators play a critical role in the ecosystem services of modern global agriculture. While honey bees (Apis mellifera; Hymenoptera: Apidae) have traditionally been considered as the essential economic pollinators of crops, recent research suggests that Osmia (Hymenoptera: Megachilidae) is also very important in improving pollination for certain crops, increasing fruit size and number of seeds, and reducing the proportion of asymmetric fruit in commercial orchards in different parts of the world¹. Osmia excavata has been considered an ideal species for apple pollination, mainly in Asia, like in north and northwest ....

Protocol

1. Preparation of the feeding tube

1. Punch a hole (~0.3 mm diameter) into the lid of a 2 mL centrifuge tube using an electric winding iron (see Table of Materials). Use such a centrifuge tube to maintain an O. excavata larva and its provision mass.

2. Preparation of pesticide

1. Dissolve the technical-grade pesticide (see Table of Materials) in acetone to acquire stock solutions of 1 x 10⁴ µg a.i. mL^-1. Then, perform gradient dilutions of the solution to more than five concentrations.
   NOTE: Chlorpyrifos at....

Results

The contents of commonly used pesticides, chlorpyrifos, imidacloprid, fendifenuron, phoxim, avermectin in provisions were less than the limit of quantification (0.01-0.02 mg kg^-1) in the control group; these results excluded the influence of pesticide residues on each treatment. The mortality with and without removing larvae from provisions after 48 h in control groups was evaluated; the results showed no significant differences (Table 1), indicating a minor human error.

Discussion

For adult pollinators, there are two main methods for measuring the ecotoxicity of pesticides. One is the contact method, in which the pesticide is applied to the prothorax of the adult insects; the other is the gastric toxicity method, in which the adult pollinators are fed with honey water containing pesticide^25,26. In recent years, it has been found that the pollination effect and eclosion rate of O. excavata are relatively low²⁷

Materials

Name	Company	Catalog Number	Comments
Abamectin	Jinan Lvba Pesticide Co. Ltd
Black-light lamps	Kanghua Medical Device Co., Ltd
Centrifugal tube box with 100 Wells	Shanghai Rebus Network Technology Co., Ltd
Centrifuge tube	Shanghai Rebus Network Technology Co., Ltd		2 mL;  Serve as bee tube
Electric soldering iron	Kunshan Kaipai Hardware Electromechanical Co., Ltd
Electronic scale	Sartorius Scientific Instruments (Beijing) Co., Ltd	3137510295
Graduated cylinder	Anhui Weiss Experimental Equipment Co. Ltd
Petri dishes (60 mm diameter)	Qingdao jindian biochemical equipment co., LTD
Pollen provision	Yantai Bifeng Agricultural Science and Technology Co. Ltd
Soft brush	Wengang Wenhai painting material factory
Solitary bees	Yantai Bifeng Agricultural Science and Technology Co. Ltd