Barbara : as far as I know there is little direct toxicity of herbicides to Lepids, unlike insecticides and some fungicides.  The main effects of herbicides are the destruction of Lepid food plants in farmland and other areas. There are several studies providing evidence supporting this and i copy one such paper below . In some EU countries farmers are now required to not spray (herbicides)  near field margins and there are conservation programmes where unsprayed areas are left around the outside of crops to encourage weed growth. In some cases these areas are sown with wild flower mixtures for insects (and birds) . 

Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population

1.      JOHN M. PLEASANTS1 and KAREN S. OBERHAUSER2

Insect Conservation and Diversity Volume 6, Issue 2, pages 135–144, March 2013

Keywords:

·        Glyphosate;

·        GMO;

·        milkweed;

·        monarch butterfly

Abstract.  1. The size of the Mexican overwintering population of monarch butterflies has decreased over the last decade. Approximately half of these butterflies come from the U.S. Midwest where larvae feed on common milkweed. There has been a large decline in milkweed in agricultural fields in the Midwest over the last decade. This loss is coincident with the increased use of glyphosate herbicide in conjunction with increased planting of genetically modified (GM) glyphosate-tolerant corn (maize) and soybeans (soya).

2. We INVESTIGATE  whether the decline in the size of the overwintering population can be attributed to a decline in monarch production owing to a loss of milkweeds in agricultural fields in the Midwest. We estimate Midwest annual monarch production using data on the number of monarch eggs per milkweed plant for milkweeds in different habitats, the density of milkweeds in different habitats, and the area occupied by those habitats on the landscape.

3. We estimate that there has been a 58% decline in milkweeds on the Midwest landscape and an 81% decline in monarch production in the Midwest from 1999 to 2010. Monarch production in the Midwest each year was positively correlated with the size of the subsequent overwintering population in Mexico. Taken together, these results strongly suggest that a loss of agricultural milkweeds is a major contributor to the decline in the monarch population.

4. The smaller monarch population size that has become the norm will make the species more vulnerable to other conservation threats.

The herbicide effect on diversity of butterflies is indirectly by host destruction. When weed hosts are as alternate,alternative,off season resource etc then impact will be acute.Generally butterfly activity is more in less disturbed eco-systems.

Dear Barbara,

The current literature mentions mainly insecticides and herbicides as harming factors on lepidopteran species. These may cause direct mortality and sublethal harms on fecundity, longevity, and decreasing food as adult nectar and larval host plants. Here you can find some references even a review and risk assessment:

http://www.nev.nl/pages/publicaties/proceedings/nummers/13/29-34.pdf

https://www.stir.ac.uk/news/2015/11/butterfly-declines-linked-to-pesticides/

http://www.sciencedaily.com/releases/2015/12/151202124613.htm

http://www.sciencedirect.com/science/article/pii/S0167880996010948

http://www.express.co.uk/news/nature/621662/Butterflies-decline-pesticides-scientists

By the way, the use of wide-spectrum volatiles (e.g. Phenylacetaldehyde) attracting both males and females caused the killing of many thousands of non-target moths in traps prepared for pest species in Hungary.

Thus, the main problem may be the eternal and unlimited desire for more and more profit without respecting the environment.

Hi Barbara:

The main impact on  insect communities including butterflies is destruction of the habitat that affect the abundance and diversity of butterflies.  Weeds can provide ecological benefits by a variety of ways. Weeds can complement the planned diversity and spatial-temporal extent of plant communities of agroecosystems with substantial increases in ecological services provided by these communities. Certain weeds extert strong qualitative effects on interactions between agroecosystem plant communities and beneficial biota at other trophic levels. Beneficial organisms (parasitoids and predators) whose diversity, abundance and provision of beneficial effects are plausibly affected by interactions with weeds include soil biota, arthropods, and beneficial microorganisms on leaf surface. Butterflies for instance take pollen and nectar from some weeds, and some are their host plant for larval survival.

I recommend read the following books:

Weed biology and management. Inderjit (ed.) 2013. Springer. 553 p.

Altieri, M.A. 1994. The influence of adjacent habitats on insect population in crop fields. In Biodiversity and Pest Management in Agroecosistems. M. Altieri (ed.) New York, Haworth Press.

Altieri, M.A. 1988- The impact, uses and ecological role of weeds in agroecosystems. In Weed Management in Agroecosystems. Ecological Approaches, M. A. Altieri and M. Liebman (Eds.). CRC Press Inc. 560 p.

Hi Barbara,

There was a very interesting paper by John Stark and colleagues in 2012: Effects of herbicides on Behr’s metalmark butterfly, a surrogate species for the

endangered butterfly, Lange’s metalmark, Environmental Pollution 164: 24-27. Here is the abstract:

Lange’s metalmark butterfly, Apodemia mormo langei Comstock, is in danger of extinction due to loss of habitat caused by invasive exotic plants which are eliminating its food, naked stem buckwheat. Herbicides are being used to remove invasive weeds from the dunes; however, little is known about the potential effects of herbicides on butterflies. To address this concern we evaluated potential toxic

effects of three herbicides on Behr’s metalmark, a close relative of Lange’s metalmark. First instars were exposed to recommended field rates of triclopyr, sethoxydim, and imazapyr. Life history parameters were recorded after exposure. These herbicides reduced the number of adults that emerged from pupation (24e36%). Each herbicide has a different mode of action. Therefore, we speculate that effects are due to inert ingredients or indirect effects on food plant quality. If these herbicides act the same in A. mormo langei, they may contribute to the decline of this species.

Cheers and see you soon,

Ryszard