Wednesday, May 20, 2009

A Nine-spotted Predator in my Backyard

While walking the dog yesterday I discovered this aphid buffet line in my backyard:

The rosy apple aphid (Dysaphis plantaginea) produces approximately 6-9 generations annually. Dense colonies (as pictured) are typically produced in middle-to-late May and are devastating to plants. After reaking havoc, the aphids will then migrate to new plants through the beginning of August. Eggs, which remain dormant until the following spring, are produced in the fall.

The aphid eggs hatch around April to produce viviparous females that will in turn parthenogenetically produce about 70 apterous virginoparae. The virginoparae will later generate a sexually reproducing generation (sexuparae) as well as males.

Their impact on plants combined with the ability to reproduce parthenogenetically makes the aphid a formidable foe – but there is a defense.
Here it comes now.

Here's a stare down between an aphid and the seven-spot ladybug Coccinella septempunctata:

The predatory attack of Coccinella septempunctata - the aphid hunter:

Coccinella septempunctata is one of several ladybeetles found in Florida, for a listing click HERE.

Throughout the United States non-native coccinellid populations are on the rise. The primary reason for this increase is most likely the establishment of exotic ladybeetles with the ability to out compete, the locals for vital food resources.

For native Florida ladybugs, those food resources are aphids, and with the exception of Neoharmonia venusta, which is a predator of psyllids (jumping plant lice), all of beetles listed above find them quite delicious.

Another contributing factor to native beetle strife may be the commercial sale and transport of ladybeetles for the purpose of agricultural defense. Although the beetles are a tremendous aid in protecting crops, the increased cross-regional exchange of fauna may be accelerating the spread of pathogenic and parasitic organisms that prey on the ladybugs.

In regards to natives being out competed for food resources, Susan Moser and John Obrycki of the University of Kentucky found that when food resources are plentiful exotic ladybeetle species, such as Harmonia axyridis and Coccinella septempunctata experience higher fecundity than the locales and can expand their numbers very quickly. When food resources aren’t as accessible the natives prove to be a heartier species and sustain reproductive rates that out pace the immigrants.

Special thanks to David Almquist from the Florida Natural Areas Inventory for help with the lady beetle ID.

Moser, S., & Obrycki, J. (2009). Competition and Intraguild Predation Among Three Species of Coccinellids (Coleoptera: Coccinellidae) Annals of the Entomological Society of America, 102 (3), 419-425 DOI: 10.1603/008.102.0310

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