6 2 Insects and plants

Transcription

1 6 2 Insects and plants Insect DIY 1. Find plant habitat 2. Find plant 3. Accept plant 4. Eat survive, reproduce Plant characteristics Shape structure Mechanical defenses trichomes Chemical defenses sap, pitch tubes 1

2 Plant characteristics that affect arthropods Leaf chemistry Volatiles Foliage / flower color Meets insect s nutritional needs Plant volatiles released after pest damage Attract predators Attract parasitoids Induce defensive responses in neighboring plants Monoculture One plant species or closely related varieties / cultivars Uniform growth stage Meets nutritional needs 2

3 Monoculture Low animal diversity many individuals of a few species Unstable easily upset by pesticide applications, cultural practices Polyculture Diverse many unrelated plant species Different plant growth stages Polyculture Many animal species, few individuals of each More stable, less easily upset 3

4 Cultural practices Planting date Plant growth stage Seedling, vegetative, reproductive, senescence Plant growth stage & susceptibility to insect damage Acceptable numbers of insects Seed Veg Repro Senes Changes in acceptable insect numbers with changes in plant growth stage 4

5 Cultural practices High plant quality > insect fertility & fecundity / faster development Cultural practices Irrigation Sap feeders adversely affected by continuous water stress - reduced water content and turgor pressure Plant water stress and pests Chewing insects reduced growth rate tougher foliage Higher conc of defensive chemicals 5

6 Normal years Rainfall effects on insect damage Yield (bu/ac) Dry Dry years Damaging level Damaging level Insect/ft row Host plant resistance Wild types have varying susceptibility to attack Plant domestication reduction or loss of some natural plant defenses Host plant resistance Any inherited characteristic of a host that lessens effects of pest attack 6

7 Components of host plant resistance Resistant varieties used more for plant diseases because insecticides *cheap * quick knockdown Grape phylloxera Aphid like insect Crawlers move from leaf (summer eggs under bark winter) to roots (year round), disperse Grape phylloxera Root galls cause stunting / death of European grapes Use American root stocks 7

8 Components of host plant resistance Non-preference Antibiosis Tolerance Non preference Plant characteristics that keep plants from being selected for egg-laying, food, or shelter 1) Moderate - only if there is a choice 2) Strong - even if there is no choice Components of host plant resistance Non-preference Antibiosis Tolerance 8

9 Antibiosis affects biology of insect Death of early instars Surviving females produce fewer offspring Smaller size and weight adults Slower development mortality Smaller food reserves Antibiosis possible causes Plant toxin Inhibition of growth or reproduction Deficient in nutritional requirements Components of host plant resistance Non-preference Antibiosis Tolerance 9

10 Tolerance plant response Grow and reproduce with injury from a pest population that would damage or destroy a susceptible host Biotype response to resistant varieties Genetically distinct strain of a species, usually designated by letters Usually physically identical Host range, host plant adaptability, plant virus transmission, insecticide resistance 50% of known biotypes are aphids Whitefly Homoptera Eggs Gradual metamorphosis Sap feeder Honeydew Mealy white wax covering on wings Adult N4 Crawler N2 N3 10

11 A, B, and Q biotype whiteflies Bemisia tabaci Greenhouse, silver leaf, sweet potato Same life cycle and host plant range Biotype Q resistant to IGR and neonicotinoid (Group 4) insecticides - imidacloprid 11