Natural events, September 2015

September was warm and dry, with less than an inch of rain for the entire month. The contrast with our deluge-inal spring is startling; it will seem very strange if this long dry spell ends up drawing the annual precipitation average back toward “normal”. One thing about Missouri weather, it’s a textbook lesson in the danger of relying on averages for accurate information about a system.

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Monarch caterpillars were present, though we saw fewer caterpillars than last year, in spite of allowing lots of Common Milkweed to grow for their benefit. I (Joanna) found the Hermit Sphinx (Sphinx eremitus) caterpillar on wild bergamot while pulling snakeroot in a goat paddock. The black spot did an impressively good job of making this look like an empty, hollowed out shell of plant or animal origin, perhaps a form of mimicry to convince predators that there’s nothing to eat here. It almost tricked me, but a second look convinced me this was a caterpillar worth bringing back to the house for ID and a picture. Since it eats mint family plants, I decided to keep it in a jar with some munchies from the herb garden. Turns out that the specimen had been visited by a parasitoid wasp, perhaps Cotesia congregata? Interestingly, the Hermit Sphinx’s relatives, the tomato-eating Tobacco Hornworms have been minimally present this year. Perhaps we can thank parasitoids for that?

Our brassicas, on the other hand, haven’t fared so well with the caterpillars. We’re used to some damage, but this year we’ve seen complete defoliation on some plants. The photo on the left, from the beginning of September, shows some of our kale that we kept through the summer, and the photo on the right shows the same plants (from a different angle) towards the end of the month:

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Note the shade cloth over some cabbages in the back of the left photo; it is an effective method for keeping adult lepidopterans from laying their eggs on the plants. There’s been very little caterpillar damage on the plants protected by shade cloth compared to those unprotected.

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The Cross-striped Cabbage Worm vastly outnumbered any other caterpillars (probably 10:1), and most of the rest were the caterpillar of the Cabbage White Butterfly.

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These unidentified caterpillars (thumb for scale) were also present (but rare compared to the others). I’m guessing these two are color variants of a single species, perhaps a species of hairstreak butterfly? Anyone know?

So, why was this such a bad year for brassica caterpillars? There are probably multiple reasons, but the extended warmth is almost certainly a factor. Caterpillars mature sooner and reproduce faster in warm compared to cool weather. From this University of Georgia site on the topic of Cross-striped Cabbage Worms:

The duration time from egg to adult ranges from 18 days under warm conditions (35°C) to two months under cool conditions (20°C). The egg takes 2-12 days to hatch (warm and cool temperatures, respectively), larval development is 2-3 weeks and the pupal stage takes 9-11 days. Newly emerged adults take 3-6 days to begin laying eggs and then lay eggs over the next two weeks. Adults live only 20 days (as little as a week under warm conditions).

Other factors that we suspect have a role: The plants were probably a bit stressed for water when the real caterpillar attack escalated, as we haven’t pampered them with irrigation in the way that we do when we’re selling crops; a lack of water/nutrients may result in plants that can’t put up a good defensive response. In combination, the plants received a bit less of our attention than in past years. Collards make a great trap crop, but a trap crop that gets ignored can result in a mass of caterpillars that move onto neighboring plants. Did leaving some brassicas over the summer help to maintain a continuous population of caterpillars? Perhaps, though a different planting of over-summered kale also hosted the best collection of a parasitoid wasp pupae that we found on any of the plantings.

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The slug eggs photographed on the left were hiding in a moist spot under a straw bale, and we think they are the eggs of the same large slug featured in the July natural events post, which we suspect is a Leopard Slug (Limax maximus). These have had a notable presence this year, the first year we’ve seen them in meaningful numbers, and we’ve been seeing them even after the weather turned dry. We also suspect that they are responsible for an especially high rate of seedling loss in August & September, especially among our young transplants of cabbage, kohlrabi, and broccoli. We never saw the herbivory in action, but they feed nocturnally, so we wouldn’t have. They did leave a mark, though, with the shade cloth in the photo on the right showing what appears to us to be a trail of slug slime.

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Enough griping about pests & caterpillars. Without caterpillars we wouldn’t have butterflies, and the warm, pleasant weather was good for watching these beauties, which seemed especially fond of some of our domestic flowers (Tithonia and Zinnia). The Monarchs were prevalent towards the end of the month, actively migrating, we assume. Clockwise from top left: Monarch, Cloudless Sulphur, Silver-spotted Skipper, and Great Spangled Fritillary (with Monarch in background).

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The spider on the left superficially resembles the Black and Yellow Garden spider, and I started my searches with spiders in that genus, Argiope. Sure enough, I found a match on BugGuide.net Argiope trifasciata. Right: not yet identified. Input from readers?

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Left: The asters were buzzing with bees. Right: Carolina Mantis on sunflower leaf.

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This smartweed, which we think is Oriental lady’s thumb (Persicaria longiseta), is an aggressive weed that just seems to show up in more places every year. It likes wet, so the 2015 population got off to an impressive start thanks to the early summer moisture. Though it mostly establishes itself in our roads and aisles, the rate at which a plant clump can spread over the course of a season is disheartening.

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Crownbeard has been a prolific bloomer this year, and now the seed heads are forming.

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The Hog Peanut (Amphicarpaea bractaeta) that was featured in the August natural events post is now putting on seeds, as well. sep_natural_flowers

Various flowers in bloom: lobelia, spiderwort, thistle (a native one).

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Left: An eft (the terrestrial, juvenile life stage of the Central Newt) on a sweet potato during harvest. We’ve come across these during sweet potato harvest before, but finding them this year was especially surprising because of the dry conditions (and the fact that we didn’t irrigate the sweet potatoes at all). Right: Northern Red-bellied Snake that we found slithering up the sidewalk in front of the house. This must be a youngster, since it was considerably smaller than an 8-10″ adult.

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Digging sweet potatoes is a good way to take stock of soil life. Many of the smaller earthworms were curled up in little pockets in the soil, apparently estivating in response to the dry conditions (for example, see this source). Some of our bigger earthworms were out and about; maybe these are capable of burrowing more deeply to moisture and thus stay active under these conditions?

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