Biopesticides - Pesticides: Evaluation of Environmental Pollution - page 599

basic β-methoxyacrylate nucleus. These reduced-risk fungicides are active at low applica-
tion rates and have low mammalian and avian toxicity. The strobilurin fungicides inhibit
cell growth at low concentrations by preventing the cells from generating energy effi-
ciently in their mitochondria. Strobilurins are active against a broad range of fungi but
are nontoxic to mammals and birds. Since they act on a single target site, these are suscep-
tible to the development of resistance. Oudemansins, first reported from mycelial cultures
of Oudemansiella mucida were subsequently isolated from submerged cultures of Xerula
melanotricha and from another basidiomycetes fungus Oudemansiella radicata . They coex-
ist along with strobilurin-A in Oudemansiella mucida and their biological activity closely
resembles that of the strobilurins. At least three oudemansins (A, B and X) known so far
exhibit considerable fungicidal activity (Clough 1993).

19.10 Biochemical Pesticides
Biochemical pesticides are naturally occurring substances that control pests by nontoxic
mechanisms. Biochemical pesticides include substances, such as insect sex pheromones,
which interfere with mating, as well as various scented plant extracts that attract insect
pests to traps. They include

1. Insect pheromones

2. Plant extracts and oils

3. Plant growth regulators

4. Insect growth regulators.

Biochemical pesticides typically fall into distinct biologically functional classes, includ-
ing semiochemicals, plant extracts, natural plant growth regulators, and natural insect
growth regulators (Figure 19.4). These classes of biochemical pesticides are described
below with examples provided for each category. There are almost 122 biochemical

Semiochemicals

Gk. Semeion , signal
Acting between individuals
within a species

Acting between individuals
of different species

Pheromones Allelochemicals

Gk. Phereum , carry Gk. Allo , different

Alarm

Allomones advantage for sender
Kairomones advantage for receiver
Synomones advantage for both parties
Apneumones from nonliving sources

Trail
Sexual
Aggregation

FIGURE 19.4
Semiochemicals.