This project has four objectives: (1)
Determine if autoclave-excludable factors in composted organic yard
waste (mulch) are responsible for suppressing avocado thrips pupation
rates beneath avocado trees. (2) Determine if humidity and temperature
influence avocado thrips survival rates in autoclaved mulch. (3) Evaluate
the mortality caused by individual natural enemy species (e.g., micro-athropods,
fungi, and nematodes) extracted from mulch on thrips pupation rates
when re-introduced into autoclaved mulch. (4) Determine if guilds
of extractable natural enemies are more efficacious than individual
species for killing thrips pupae in autoclaved mulch.
Preliminary work has indicated that
composted mulches below avocado trees significantly reduce thrips
pupation rates in comparison to non-mulched plots. The mulch we have
been testing for thrips control has been demonstrated to suppress
avocado root rot (Phytophthora cinnamomi) because of the
presence of antagonistic micro-organisms that flourish in mulches.
Additional benefits of applying organic mulches in orchards include:
increased water conservation, improved soil fertility and weed control.
As a result, use of mulches can increase yields of avocado fruit by
up to 13%. The work we propose here will enhance our understanding
of suppressive mechanisms in composted mulch that reduce avocado thrips
Abiotic factors such as humidity or
temperature may effect thrips pupation rates in the mulch, while biotic
factors such as generalist predatory micro-arthropods, entomopathogenic
fungi, or entomopathogenic nematodes may contribute to thrips mortality.
Abiotic and biotic mortality factors will both be evaluated in the
laboratory using field collected second instar avocado thrips larvae
(this pest is inordinately difficult to maintain in culture). Identification
of efficacious natural enemies amendable to mass-rearing may provide
a suite of individual biological control agents, or even a controlled
mixture of these agents in a more resilient “biological control
community”, which may be used to amend mulches prior to their
being laid in orchards for thrips control.