Selecting insecticides or miticides with less impact to honeybees for use in Cucurbit crops

Published: June 1, 2012

Insecticides are used to get rid of unwanted insects. Unfortunately, honey bees and most other beneficial insects or mites are greatly affected by insecticides. There are several ways honey bees (and other bees) can be killed by insecticides. One is direct contact of the insecticide on the bee while it is foraging in the field. The bee immediately dies and does not return to the hive. In this case the queen, brood and nurse bees are not contaminated and the colony survives. The second more deadly way is when the bee comes in contact with an insecticide and transports it back to the colony, either as contaminated pollen or nectar or on its body. This article discusses the relative toxicity of insecticides to honey bees and other beneficial insects with a focus on products listed for cucurbits in the 2012 Midwest Vegetable Production Guide given the high need for these crops to get sufficient pollination services.

Cucurbits have the male and female flower parts in separate flowers (yet still on the same plant) and therefore insects are needed to transfer pollen from male flowers to female flowers while collecting nectar and pollen. In general terms, the more bee visits per flower, the greater the number of seeds per fruit, the larger the size of the fruit, and the fewer number of mishapen fruit.

The 2012 Production Guide lists 29 different insecticide/miticide products that can be used in cucurbit crops (squash, pumpkins, melons, cucumbers, etc.). Of these, 8 insecticides are reduced-risk products and 2 can be used in organic production. Cornell University developed a method to estimate how toxic insecticides are to fish, birds, bees, and other beneficials, combined. This method yields a single value that for the purposes of this article can be called Ecological Impact Value (EIV). In brief, it is calculated taking into account the inherent toxicity of the chemical, the % active ingredient in formulation, the rate at which is being used (for the calculations the high rate was used), and the number of applications. The table below provides the ranking of insecticides listed in the 2012 Midwest Production Guide for cucurbit crops, from the most toxic (higher EIV) to the least toxic (lower EIV) to bees and other beneficials. The top 10 most toxic materials are highlighted in red. Check the 2012 Production Guide for specific uses (crops, pests) of the materials listed below.

In addition to the above data, the following recommendations can minimize the risk of inadvertently killing bees and other beneficial insects:

• Use less toxic, rapidly degradable pesticides – The table above can help you select effective yet the least toxic (to non-target organisms) insecticides.
• Choose the appropriate formulation- The appropriate choice of formulation is another way to avoid honey bee pesticide kills. Pesticides come in different formulations: dusts (D), wettable powders (WP), soluble powders (SP), emulsifiable concentrates (EC), solutions (LS), and granulars (G). Solutions, emulsifiable concentrates, and granulars are the best formulations to use. Solutions and emulsifiable concentrates dry quickly and do not leave a powdery residue unlike the dusts and wettable powders. Granulars are similar to dusts but are larger in particle size.
• If at all possible do not spray blooms directly with pesticides. If the bloom needs to be sprayed, apply the pesticides in the evening hours.

Editor's note:
The Midwest Vegetable Production Guide for Commercial Growers also addresses this topic. For the 2012 edition it starts on page 25 and provides a list of pesticides and their toxicity on page 26. The scale provided in this article is easier to use. Look for more information on this topic in upcoming newsletters.