When and how to apply Heterorhabditis indica for small hive beetle control? / by Ganpati Jagdale

Small hive beetles

Small hive beetles, Aethina tumida are the most devastating insect pest of honey bee (Aphis mellifera) hives (Photo 1). Both adults and larvae of small hive beetle cause direct and indirect damages to honeybees. In case of direct damage, larvae of  small hive beetle directly feed on the honeybee brood, honey. pollen and destroy honeycombs. In case of indirect damage, both adults and larvae of small hive beetle spread yeast, Kodamaea ohmeri into the colony and yeast that grows on the honeycombs causes fermentation of honey, which is not suitable for human consumption or as the food for honeybees.

 Photo 1. An adult of small hive beetle and honeybee hive.

Photo 1. An adult of small hive beetle and honeybee hive.

Small hive beetles complete some part of their life cycle in the hives and some in the soil. Briefly,  adults of small hive beetles overwinter in the beehives. During spring eggs laid by small hive beetles females hatch into young larvae inside the beehives where they start feeding on honey, pollen and brood and become mature. Mature larvae then move out of beehives in the soil where they pupate. Small hive beetle adults emerge from pupae and move back into beehives. As several overlapping generations are completed from April through November, new generation larvae constantly move from hives and pupate in the soil in 3-4 feet radius around the beehives (Photo 2).

 Photo 2. Movement of mature larvae of small hive beetles

Photo 2. Movement of mature larvae of small hive beetles

Control of small hive beetles

Since small hive beetles can destroy honeycombs, and bee colony, and deteriorate quality of honey, timely control of these beetles is essential to stop the complete destruction of honeybee colonies and prevent economic losses to beekeepers. Control of small hive beetles with chemical pesticides can not be a safe option because of their detrimental effects on the bees and consumers of honey. Currently, beneficial entomopathogenic nematodes called Heterorhabditis indica are used as alternatives to chemical pesticides for controlling small hive beetles.

Heterorhabditis indica nematodes

Heterorhabditis indica nematodes are microscopic, insect- parasitic and commercially produced roundworms (Photo 3). When Heterorhabditis indica nematodes applied into the soil around beehives, they search, infect and kill soil-dwelling larvae and pupae of small hive beetles. Briefly, in the soil, once nematodes find either larva or pupa of small hive beetles, they enter into their body cavity through the natural openings like anus, mouth and spiracles and release symbiotic bacteria (Photorhabdus spp.) in the blood. In the blood, bacteria multiply quickly, cause septicemia and kill larva or pupa within 48 hours of infection that in turn completely stops the emergence of next generation of small hive beetles.

 Photo 3. An infective juvenile of  Heterorhabditis indica  nematodes

Photo 3. An infective juvenile of Heterorhabditis indica nematodes

How to apply Heterorhabditis indica nematodes?

The main aim of application of beneficial Heterorhabditis indica nematodes in the soil is to kill soil-dwelling mature larvae and pupae of small hive beetles so that the next generation adults will not emerge from pupae and invade the beehives again. Heterorhabditis indica nematodes are supplied as infective juveniles on alginate gel and they can be easily mixed with tap water and applied using a watering can with a sprinkling head (Photo 4).

 Photo 4. Use watering can for the application of nematodes

Photo 4. Use watering can for the application of nematodes

For effective control, Heterorhabditis indica nematodes should be applied at the rate of 23000 infective juvenile nematodes per square foot area (which is equivalent to 1 billion nematodes per acre) covering about 3-4 feet area all around the beehives upon their arrival. However, for some reason, if it is not possible to apply them immediately, then they can be stored at 10°C (50oF) for a week without affecting their infectivity (virulence).  For even distribution of nematodes around the beehives, make sure that nematodes are thoroughly mixed in the water and constantly agitated at the time of their application, to prevent them from sinking and settling to the bottom of watering can.

When to apply Heterorhabditis indica nematodes?

Heterorhabditis indica nematodes can be applied starting from April through November for targeting and killing both the mature larvae and pupae because these stages should be always present in the soil due to several overlapping generations completed by small hive beetles during these months. However, make sure that the nematodes are applied when environmental conditions like soil moisture, temperature and ultraviolet (UV) radiation are optimum.

For example, Heterorhabditis indica nematodes need a film of water for their free movement in the soil to seek both the larvae and pupae of small hive beetles but if soil is too dry, the will deissicate and may die before finding host. Therefore, irrigate areas around beehive before and after application of nematodes. Since extreme cold or hot soil temperatures can kill nematodes, apply nematodes when soil temperature is between 24°C (75.2°F). Since exposure to UV light can kill nematodes instantly, apply nematodes early in the morning or late in the evening when intensity of UV radiation is low.