Acute toxicity effects of agrochemicals on honeybees (Apis mellifera jementica) in Tigray region of Ethiopia

Gebrecherkos Yeebyo, Amssalu Bezabeh¹ and Asaminew Tassew²

Mekelle Agricultural Research Center
gyeebyo@gmail.com
¹ Holeta Bee Research Center
² Bahr Dar University

Abstract

Oral acute toxicity effects of six agrochemicals; (Malathion 50% EC, Profenofos 72% EC, Karate 5 EC, 2, 4-D, Pallas 45 OD and Mancozeb 80% WP), were evaluated under laboratory condition. All the tested agrochemicals were found to be toxic to the local honeybee race compared to negative control (50% honey solution) administered through oral feeding. Malathion 50% EC and Profenofos 72% EC exhibited fast action, took less than 2 hours after exposure, in imposing death for 100% of the experimental adult honeybees. Karate 5 EC and 2, 4-D took longer time (24 hours) to kill the same percent of the experimental adult honeybees. It is advisable not to apply those products or allow them to drift to blooming crops or weeds while honeybees are actively visiting the treatment area.

Keywords: biodiversity, exposure, fast-acting

Introduction

Honeybees are one of the most important beneficiary insects which play vital role in pollinating the crop and the forest plants. Almost 90% of the angiosperms depend on pollinators to survive and honeybees are the best-known pollinators (Baskar et al 2016). The value in terms of agricultural production, achieved by pollinating bees, was estimated to be 10 -15 times higher than the value of the production of honey and wax (Goulson et al 2015).

Beekeeping significantly contributes livelihood and to the Ethiopia economy. From 1.5 to 1.8 million households earn various levels of income from beekeeping. “Tej” to which the major proportion of local honey goes is a high calorie traditional drink providing significant additional rural employment and incomes (Desalegn Begna 2014). An average of 15 million USD is obtained annually from the sale of honey, both in local and world markets (Workneh Abebe et al 2008). Honeybees also increase the yield of Guizotia abyssinica, Allium cepa and Vicia faba by 43%, 84% and 28% respectively via pollination services (Adimasu Addi et al 2000; Adimasu Addi et al 2006; Haftom Gebremedhin et al 2014).

Honeybees are not immune to biological and physical threats, and they are currently under tremendous pressures from natural and human interference, including pests, parasites, pathogens, agrochemicals, and loss of natural foliage (Potts et al 2010; Goulson et al 2015). Honeybees are often adversely impacted (although unintentionally) by farming practices, such as the loss of favorable natural habitats, and direct poisoning from agrochemical treatments (especially seed coating and foliar sprays) (Desneux et al 2007).

Honeybees (Apis mellifera), the most common managed pollinators, have experienced exacerbated rates of colony losses across the global North in recent years, from an average of 30% in the United States to as high as 85% in the Middle East (Neumann and Carreck 2010). One stressor, exposure to agrochemicals, has been, and remains, an important focus for research (Goulson et al 2015).

The use of agricultural inputs in Ethiopia, including agrochemicals, were introduced to the small holder farmers through various agriculture extension systems since the 1960’s (Gizachew Assefa 2011). Since then the use of agrochemicals showed a steady growth and currently with the development of the flower sector and expansion of irrigation the importation of agrochemicals on average has reached to over 2400 tonnes per annum (Gizachew Assefa 2011).

In the Tigray Region, new concerns arose regarding honeybee toxicity from indiscriminate use of agrochemicals. Some farmer beekeepers in the region are now claiming they are left with empty hives and forced to leave their long-lived practice of beekeeping due to the unwise and careless use of agrochemicals.

Therefore, this study was conducted to determine oral acute toxicity to honeybees of commonly applied agrochemicals.

Objectives

· To evaluate the acute oral toxicity of the agrochemicals

· To determine level of toxicity of the commonly applied agrochemicals

Laboratory procedure

Oral acute toxicity effects of six agrochemicals (Malathion 50% EC, Profenofos 72% EC, Karate 5 EC, 2, 4-D, Pallas 45 OD and Mancozeb 80%WP) were examined via feeding mode. The effects these agrochemicals impose on adult honeybees were assessed according to the following guide lines of OECD (1998a), EPPO (2010b) and CEB (2011). Commercial formulations available in the local market were used. The recommended dose levels for crop treatment (field concentration) of the agrochemicals were identified from the labels and applied at volumes appropriate to laboratory level conditions.

Adult worker honeybees were taken from a healthy, strong and queen-right single colony in Mekelle Agricultural Research Center Apiary site. The bees were collected from the hive entrance in the early morning and put in well-ventilated plastic jars. After transporting to the experimental room, the honeybees were anaesthetized with CO₂ for ease of counting and finally held in easy to clean and well-ventilated wooden cages (5.5 x 8.5 x 10 cm). Moribund bees, affected by the handling or otherwise, were rejected and replaced by healthy vital bees before starting the test. The bees were held in the dark experimental room at a temperature of 25 ± 2°C with relative humidity, normally around 60-70%, during the trial periods (OECD 1998).

The mortalities caused by individual agro-chemicals were compared with a positive toxic standard chemical (Dimethoate 40% EC) and negative controls (50% honey solution).

Feeding Test

Thirty predetermined healthy adult worker honeybees were placed in each cage and starved for 2 hours before the test began. Formulations of the agrochemicals were dissolved with distilled water. A glass tube 50 mm long and 10 mm wide with the open end narrowed to about 2 mm diameter was used as feeder unit. The bees were provided with formerly prepared 50 % honey solution containing the recommended concentration (10ml/bee) of the test solution to determine the toxicity. Each treatment (agrochemical) was replicated three times in a random design (CRD). The acute oral toxicity of the agrochemicals tested was compared with a highly toxic standard reference 0.3 ml of Dimethoate 40% EC) (Gough et al 1994) and a separate negative control (50 % honey solution). Finally, mortality rates were recorded starting from 15, 30, 45 minutes, and up to 1, 2, 4, 6, 12, 24, 48 h. The honey solutions were offered ad libitum to the honeybees for the entire trial period.

Percent of mortality of the honeybees caused by each agrochemical was corrected (using Abbott 1925 model) as follows:

Statistical analysis

Analysis of variance was done by ANOVA (SPSS version 20) and Tukey’s separation of means at 5% level of significance.

Results

The tested agrochemicals differed in imposing acute mortality effects on the adult honeybees (Table 2). Malathion 50% EC, Profenofos 72% EC and Karate 5 EC were highly toxic and all induced 100% death rate of the bees (Figure 1). Malathion 50% EC and Profenofos 72% exhibited fast action, with less than 2 hours after exposure to kill 100% of the adult honeybees. These agrochemicals were equivalent to the standard toxic agrochemical, Dimethoate 40%EC, in imposing the death of 100% of the experimental adult honeybees during the same trial period. Karate 5 EC and 2,4-D took longer time (24 hours), to kill the same percent of the experimental honeybees(Figure 2).

The LD₅₀ of the agrochemicals were determined under laboratory condition. Accordingly, four out of the tested agrochemicals (Malathion 50% EC, Profenofos 72% EC, Karate 5EC and 2,4-D) were in the range of highly toxic classification (acute LD50 < 2μg/bee; Table 1).

Figure 1. Mortality rate caused by different agrochemicals

Mancozeb 80%WP and Pallas 45 OD were less toxic than the other agrochemicals in acute toxicity effects but higher than the non-toxic negative control (Table 2). These results are supported by the LD ₅₀ of these two agrochemicals; confirmed as belonging to the range of slightly toxic classification (acute LD₅₀ 11-100μg/bee) (Table 1). Sub-lethal exposures to agrochemicals, especially fungicides and some herbicides, often produce stress in animals, because the organisms try to metabolize and get rid of the toxic chemicals quickly using large amounts of energy. The indirect effects caused by herbicides cannot be ignored (Francisco and Koichi 2016).

Figure 2. Mean adult honeybee mortality by different agrochemicals

Discussion

The results of the current study are in accordance with previous research conducted in Pakistan by Khan et al (2016) that showed Malathion 50% EC is highly toxic to honeybees and its residual toxicity effects persist up to 10 days. Malathion 50%EC affects honeybees in different ways that relate to acute, chronic or sub lethal intoxication, all contributing to the honeybee death (Desneux et al 2007). Malathion 50% EC is highly toxic to a number of other hymenopterous insects in addition to the honeybee (Levin et al 1968). Due to its broad-spectrum toxicity characteristic, Malathion 50% EC aerial bait sprays have been prohibited in Guatemala since 1987 (Villaseñor et al 2000). This study is also supporting the ideas of Amssalu Bezabeh et al (2012a) and Dawit Melisie et al (2015).

Karate 5 EC is highly toxic when bees are exposed to direct application at normal use rates (USEPA 1988). Lambda-cyhalothrin (Karate 5 EC) is the most dangerous to honeybees when sprayed to agricultural crops. The micro-encapsulated formulation of lambda-cyhalothrin (Karate 5 EC) is particularly hazardous because honeybees can carry the microcapsules containing the concentrated chemical to the hive (Francisco and Koichi 2016). These products are highly toxic to honeybees exposed to direct treatment on blooming crops or weeds. This can be attributed to the fact that those agrochemicals are insecticides in nature and honeybees are insects, therefore, susceptible to any poison designed to kill insect pests. The findings of the current study do not support the previous research by Turner and Larry (1993) who reported Karate 5 EC (Lambda-cyhalothrin) spray on crops had little effect on the honeybee foragers but found it to be highly toxic and caused heavy losses if applied in combination with fungicide.

2, 4-Dichlorophenoxyacetic acid, commonly known as 2, 4-D, a widely used herbicide in the study area to control broad-leaved weeds, was found to be highly toxic (killed 95%) to the local honeybee race ( Apis melifera jementica) when ingested with food. This outcome is contrary to that of Amssalu Bezabeh et al (2012a) who found that the agrochemical 2, 4-D didn’t impose significant adult honeybee mortality when ingested with food. The difference in agro-ecology (arid midland vs highland) as well as local honeybee race variations ( apis mellifera jementica vs apis mellifera bandassi) probably account for the different results. For many agrochemical substances, a linear relationship links ambient temperature and LD ₅₀s, positively with some and negatively with others; hygrometry is also a factor of variation (Medrzycki et al 2015). At the individual level, subspecies and strains of honeybees are not equally susceptible to a given dose of active ingredient (Suchail et al 2000).The current study is also in contrast with previous reports of “Beyond Pesticides Factsheet” (2003) which showed that 2, 4-D and its salts and esters are predicted to pose minimal risk to pollinators, like the honeybee, and other beneficial insects.

Herbicides are not toxic to bees, but they disturb the environment in which bees and other pollinators live (Francisco and Goka 2016). Consequently, bees find it more difficult to collect the variety of pollen that is required for a healthy bee diet. Poor bee nutrition due to scarcity of flowers is the indirect result of continuous herbicide applications in crops and forestry areas over many decades.

Conclusions

• The agrochemicals Malathion 50% EC, Proift 72%, Karate 5 EC, 2, 4-D, Pallas 45 OD and Mancozeb, used for crop protection, harm honeybees when ingested with food.
  
  
• These substances are among the most potent agrochemicals toxic to honeybees and should not be applied during the flowering period of crops and weeds.

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Received 9 November 2019; Accepted 25 January 2020; Published 2 March 2020

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