No.11 Article 1 Technical aspects of my internship: Insects and disease
By Romy Krueger | Newsletter No. 11 April - May 2009

There are six alley cropping sites utilizing Inga sp. trees at the FunaVid property. Spacing between tree rows and individual trees varied from site to site to investigate which spacing is most beneficial for crop production. All but one site are located in the mountains and trees are planted on a slope.

At all sites trees were randomly selected and their leaves were examined for insects present, damage to leaves, and disease incidence. For the smaller trees I tried to look at all the leaves, but had to sample the leaves of larger trees.  Leaves were examined usually from below the canopy and were inspected more closely if anything suspicious was found. In the laboratory leaf samples indicating disease were examined with a dissecting microscope, before slides were prepared and inspected under a compound light microscope. Insects were examined using a dissecting microscope.

In addition, soil samples were taken at all sites to survey for nematodes present in the soil.  These are microscopic worm-like organisms and were extracted using Baerman trays. Here the Baerman tray was a plastic sandwich box that was filled with water. A sieve, which was covered with filter paper, was placed into the water. Soil was then placed into the filter paper-covered sieve and covered with the overhanging edges of the filter paper. Nematodes will move from the soil into the water. Soil samples were collected using the following method: The field was divided roughly into 3 zones: upper, middle and lower zone.  In each zone two locations were chosen: one in the root zone of a tree and one in the row middle. Since there were three zones and two samples in each zone were collected, six samples total were obtained.

The most frequently encountered pests were whiteflies (Hemiptera: Aleyrodidae) (Fig. 1), which in vegetable production are very important pests, because they cause silvering of leaves (decreasing photosynthesis) and can transmit viruses, which in turn cause serious plant diseases. I did not notice that trees were severely affected by the feeding activities of whiteflies.   This may have been because their numbers were not high enough yet. However they may affect crops later grown in the alleys. I was unable to determine the species, because of the lack of literature available for identification of locally occurring insects. Therefore it is hard to say if the species affecting Inga sp. would affect any crops planted next to Inga sp., but it is a possibility. Other insects likely to affect Inga sp. negatively are leaf-skeletonizing (forming webbing over feeding area) unidentified lepidopterans (Fig. 2) and an unidentified coreid (Hemiptera-Coreidae) (Fig. 3). These are commonly known as leaf-footed and squash bugs (Coreidae) In addition other species of the family Coreidae were present, but they did not appear to be as abundant as the foremost mentioned species.

 

Hemiptera- Aleyrodidae                       Unidentified lepidopterans

Fig. 1 Fig. 1 Hemiptera- Aleyrodidae                                                                       Fig. 2

Hemiptera-Coreidae           

Fig. 3 Hemiptera-Coreidae

There were also several families of various hoppers present (Hemiptera-Cixiidae Fig. 4, Membracidae Fig. 5, Flatidae Fig. 6) that were feeding on the foliage of the trees, but none of them appeared to be present in great numbers.

Membracidae

Cixiidae

 

 

 

 

 

 

 

Fig. 4 Cixiidae                                                                                        Fig. 5 Membracidae

Flatida

Fig. 6 Flatidae

Most leaves examined had leaf-mining insects present, probably of lepidopteran origin. This feed right under the epidermis, which creates a visible feeding trail that indicates their presence. Eventually they pupate (the larvae do the feeding) and then metamorphose into adults, which chew a little exit hole and emerge from the leaf. These can be flies, wasps, or moths.

At two sites Ortheziid scales (Hemiptera-Coccoidea-Monophlebidae-Crypticerya spp.) were found. These attached mainly to the main leaf veins (Fig. 7 and 8). They appeared to reproduce prolifically and may become a greater problem.

Ortheziid scales                       Ortheziid scales

Fig. 7                                                                                                                                Fig. 8

Several trees were subjected to galling, caused by an unknown agent (Fig. 9-11). Dissection of various galls revealed the pupae of an unidentified insect. Galling, if a leaf was affected, was usually heavy, often covering the entire underside of a leaf. In general several leaves of one tree were affected. These galls were small brown oval structures, covered with rough hairs. At the point of attachment the galls caused browning of the leaf tissue. Since they covered the leaf, they may have reduced photosynthesis, because less photosynthetic tissue was available, which may have limited development, growth, and reproduction.  These specific galls were found on almost all trees that were inspected. But since trees were only surveyed and no real experiment was conducted it is difficult to tell if they actually impacted the trees.                      

Galling

Galling

 

 

 

 

 

 

 

Fig. 9                                                                                                                               Fig. 10

Galling

Fig. 11

Furthermore the lepidopteran family Hesperiidae was present (Fig. 12). The larvae roll a leaf around their bodies and consume the leaf from the inside out while it is growing.

 

 Lepidoptera-Hesperiidae-  Pyrginae-Telemiades sp.

Fig. 12 Lepidoptera-Hesperiidae-

Pyrginae-Telemiades sp.

 

Also in three instances (three individual trees) armored scales (Hemiptera-Diaspididae) of three different species were discovered (Fig. 13-15), one of which inhabited a small tree that was dying, apparently because of the scales' actions. Since the occurrence of scales was limited to one experimental site and affected only three trees at that site, scales so far do not seem to play a major role.

Hemiptera-Diaspididae

 Diaspididae-(Parasaissetia/Eucalymnatus?)

 

 

 

 

 

 

 

Fig. 13 Diaspididae-(Parasaissetia/                                                                          Fig. 14

Eucalymnatus?)

Hemiptera-Diaspididae

Fig. 15

Although many potentially harmful insects were observed and collected, there was an abundance of beneficial insects present, which may be why potentially damaging insects were at low numbers and did not seem to affect trees severely (Fig. 16-21).

Coleoptera-Lampyridae=Photinus sp.?

Eggs of Neuroptera

 

 

 

 

 Hemiptera-Reduviidae- preying on  Hemiptera-Coreidae

 

 

 

 

 

 

 

 

 

 

Fig. 18 Hemiptera-Reduviidae- preying on

Hemiptera-Coreidae

 

Mantodea-Mantidae

 

Diptera=Asilidae feeding on Hemiptera=membracidae                       Ants collecting nectar on Inga

There was some evidence of rust occurring on leaves of several trees (Fig. 22 and 23). However isolation could not confirm this initial diagnosis. The leaf material was dried out by the time it could be examined, which may have prevented successful isolation. Rust is a fungus, which if severe could potentially harm the trees. There are treatments available for rust, but these would most likely be too expensive for local farmers. Furthermore, before any treatment is applied it should be determined if rust is really present at the sites. Blind application, because of a hunch should never be performed. Trees should be continuously monitored for the presence of rust. However, if the brown spots were indeed rust it did not appear to be a severe problem. No other disease symptoms were observed.

Rust on Inga leaves                       Rust on Inga leaves

NEMATODES

Because of the lack of the proper microscope equipment only a very limited investigation was possible. However, it appeared that there were only very few nematodes present in the soil.  They belonged to two genera (Fig.24-26). Nematode 1 is suspected to be a bacteriovore, because of the lack of a stylet and the general appearance of the feeding apparatus. It most likely belongs to the genus Acrobeloides (Fig. 24). Nematode 2 might be a plant parasite, although this is unlikely since its stylet appears to be weak. It is more probable to be a fungivore belonging to the genus Filenchus (Fig. 25 and 26). Both nematodes are a common occurrence in most soils.

A stylet is a feeding organ characteristic of plant parasitic nematodes. Plant parasitic nematodes are nematodes that can harm plants. They primarily feed on the roots of plants, but there are also some foliar ones, which were not of concern in this case. Feeding activity damages the roots, which impairs the plants' ability to take up nutrients and water. Other studies3 have found that roots are concentrated in the upper soil layers. This is due to the heavy mulch formed by abscised Inga leaves. Roots grow into the mulch rather than into the soil, which means that roots largely escape nematodes as they live in the soil and not in the mulch.   Soil samples were taken in the upper 10-20 cm.

 

Nematode                       Nematode

Fig. 24 Nematode 1                                                                             Fig. 25 Nematode 2

Nematode showing stylet

Fig. 26 Nematode 2 - stylet

CONCLUSION

Readers have to be aware that this was a survey rather than an experiment, meaning the purpose of this study was to gain a general overview of insects, diseases, and nematodes present at the Inga sites. This means that the observations made only give a brief glimpse of what organisms are present in a typical Inga planting site. Without a real experiment that uses several treatments (exclusion of some organisms, no exclusion,) and replications and which is repeated over more than one season, it is difficult to tell what if any impact insects, diseases, and nematodes had, since there was no control present (trees that were growing without being impacted by any potentially harmful organisms). Furthermore, since surveys were made without a crop present in the row middles, it is also difficult to estimate if organisms affecting Inga trees would have affected crops grown between Inga trees. None of the organisms found at the Inga sites appeared to have a severe impact (no dying trees or severely damaged trees were found), but if impairment of growth, development, and reproduction is caused by any of the found organisms can only be determined by conducting an experiment.

 

ACKNOWLEDGEMENTS

Specials thanks to Dr. Lyle Buss, Dr. Robert McSorley, Dr. James E Lloyd (Univ. of Florida), Dr. Dan Janzen, Dr. Winnie Hallwachs (University of Pennsylvania), Dr. Takumasa (Demian) Kondo (CORPOICA), Andre Basler and Dr. Corinne M. Unruh (Univ. of California, Davis) who helped me with the further identification of the insects and nematodes, and of course Dr. Guillermo Valle with whom I worked.

Also, this internship was partially made possible by travel funds provided by the DPMSO (Doctor of Plant Medicine Student Organization), room and board provided by FUNAVID and Ligia and Guillermo Ramos of Honduras

References

1. Entomological collection of CURLA

2. Triplehorn, C.A. and Johnson, N.F. 2005. Borror and Delong's Introduction to the Study of Insects, 7th edition, Brooks/Cole, Thomson Learning, Inc.

3. Michael R. Hands Unpublished report 2003

All photographs were taken by, and are the Copyright of, Romy Krueger.  The original photos are of a very high quality and have been reduced here for the web.  If anyone wants to see the higher quality ones for purposes of study please email contact@rainforestsaver.org