1 Insect-Plant Interactions Plants as insect food 4 th Lecture

2 Plants as insect food Two basic question –First, What do plants offer to insects by way of nutrition? –Second, What do insects need for optimal growth and reproduction?

3 Plants as insect food 1- The chemical composition of plants 2- The nutritional requirements of insects vary between species and developmental stage and environmental conditions. What plants provide and what insects require What plants provide and what insects require

4 Plants as insect food It is appropriate to compare the chemical composition of insects with that of plants ? Fig. 5.1

5

6 Plants as insect food InsectsPlants 8-14%2-4%Protein 22.8 j/mg 18.9 j/mg Caloric value

7

8 Table 5.1

9 Plants are suboptimal food The food of insect herbivores consists of dilute nutrients in a matrix of indigestible structural compounds, such as cellulose and lignin and variety of allelochemicals Exert toxic effects Interfere negatively with digestion The quantitative ratios of nutrients in plant differ than insects need

10 Plants are suboptimal food The nutritional requirements of insect are generally the same as animals, insect are not able to synthesize sterols. So, insects extract sterols from their food beside to amino acid, carbohydrates, lipids, fatty acids, vitamins, trace elements.

11 Plants are suboptimal food Polyphagous larvae of corn earworm (Helicoverpa zea) grow best on an artifcial diet with a protein:carbohydrate ratio of 79:21. Conversely, Locusta migratoria nymphs require 50:50. Why?

12 Plants are suboptimal food Locusta migratoria Helicoverpa zea

13 Plants are suboptimal food The corn earworm grow fast and therefore need protein-rich food, the locust is characterized by slower growth and higher activity level activityGrowth lessFasterEarworm moreSlowerLocust

14 Plants are suboptimal food needactivityGrowth More protein lessFasterEarworm More carbohyrate moreSlowerLocust

15 Plants are suboptimal food The artificial diets that support growth better than natural food plants young cutworm larvae (Agrotis ipsilon) gain 12 times as much weight as those raised on susceptible corn plant. Fig. 5.3

16 Plants are suboptimal food

17 Aphids Scale insects

18 Scale insects The bacteria in question are not disease organisms; rather, they live symbiotically with their scale-insect hosts, a relationship that is vital to both organisms. The bacteria derive their very livelihoods from the insects, and the insects in turn depend on their resident bacteria for help surviving on a diet that is conspicuously lacking in protein. Yet despite the aid the bacteria render the insects, the bacteria may still interfere with the insects' genetics. To understand why, it is helpful to understand something about the lives of scale insects and the bacteria that live reside them.

19 Plants are suboptimal food Conclusion The most susceptible plants are in fact are well defended against insect attacks. The most susceptible plants are poor food sources from a nutritional point view. The most susceptible plants are poor food sources from a nutritional point view.

20 Protein Most plant tissue consists of Carbohydrate-Cellulose Most insect tissue consists of protein Protein in plants Protein in insects Aromatic amino acids are amino acids which include an aromatic ring. amino acidsaromaticamino acidsaromatic

21 Protein The balance of amino acids that constitute plant proteins differs from the dietary requirements of insects The balance of amino acids that constitute plant proteins differs from the dietary requirements of insects Insects need higher levels of aromitic amino acid, such as phenylalanine and tryptophan, than present in plant protein. Insects need higher levels of aromitic amino acid, such as phenylalanine and tryptophan, than present in plant protein.

22 Amino acids phenylalanineLysine

23 Protein High nitrogen levels may coincide with metabolically useless nitrogen compounds such as alkaloids, or with tannins, in which in some cases reduce digestive efficiency. In this respect phloem –feeding species are in more privileged position than chewing insects, because nearly all nitrogen- containing compounds in phloem sap be utilized.

24 Protein Xylem forms a less suitable food source than phloem ( 0.1% and 1% of nitrogen in the phloem and xylem respectively. Leaf-hopper suck enormous of sap to meet their nitrogen and carbohydrate demands. Feeding rates can be as high as 300 to 1000 times the body weight per day. Individual of leaf-hopper consumes 3.9 ml water, 57 µmol organic carbon, and 21 µmol nitrogen during a day of feeding.

25 Protein Leaf-hopper suck enormous of sap to meet their nitrogen and carbohydrate demands. Feeding rates can be as high as 300 to 1000 times the body weight per day. Individual of leaf-hopper consumes 3.9 ml water, 57 µmol organic carbon, and 21 µmol nitrogen during a day of feeding. The daily intake of carbon about 14% of the amount of carbon present in the body of insect. The daily intake of carbon about 14% of the amount of carbon present in the body of insect. The daily intake of nitrogen about 29% of the amount of carbon present in the body of insect. Fig 5.4

26 Protein The amount of nitrogen extracted by 16 leaf- hopper individuals during three weeks experiment amount of 48% of total plant nitrogen in case of soybean plant.

27 Protein Caution Faster larval (lepidoptera) growth, due to high nitrogen contents, caused pupal mortality and reduction in adult size. Insect performance as a whole is in this case not correlated with a higher growth rate during the larval stage on nitrogen- enriched host plants.

28 Nitrogen is an indicator of food quality The application of nitrogen fertilizer to plants can be expected positively to affect herbivore performance. But negative effects have been also reported. 115 studies in which insects grew better with increased plant nitrogen. 44 studies indicated a decrease of in insect performance with high nitrogen concentration. Why?

29

30 Why? 1- The flush feeder insects species that are adapted to high nitrogen levels in their food, would respond positively to an increased amount of nitrogen being transported to the growing tissues, whereas, senescence feeders would respond negatively to decreased export of nitrogen from senescing tissues

31 Why? 2- Nitrogen fertilization may cause kind of physiological and morphological alternation to plant and affect secondary metabolism, resulting in increased production of defense substances. Morphological changes may include an increase of leaf surface and leaf thickness. Thus, nitrogen fertilization-induced changes naturally alter the value of the plant as a home for the herbivore and its natural enemies

32 Consumption and utilization: Consumption Fast-growing insects consume large amounts of food. Their gut occupies most of the body cavity. Food passage through the gut is fast and often takes only a few hours in leaf- feeding insects.

33 Consumption and utilization: Consumption Food passage through the gut in hours 1.5 Schistocerace gregaria 1 An Aphid More than one hour Cicadellid

34 Consumption and utilization: Consumption Young Caterpillar consume at a rate of six time their body weight per day. Adult locusts eat daily about their own weight of food. Sap feeding spittlebugs may ingest xylem in amount of times their body weight per day. As result, mature larvae often weight several times their weight at hatching (Silkworm, Bombyx mori).

35 Consumption and utilization: Utilization

36

37

38

39

40